text:
Generate the longest error message in C++
Write a short program, that would generate the longest possible error message, in a standard C++ compiler (gcc, cl.exe, icc, or clang).
The score of each entry is the number of characters in the longest error message the compiler emitted. Types included in your source code and quoted by the compiler are counted as a single character.
Cheating
You can always redefine a template in template in template with long names, but I expect something creative. I tried to prevent some of that by the last rule, but of course the rules can be better, and I'll be glad for improvements.

Edited the tags. I admit that [kolmogorov-complexity] is a bit of a stretch, but I think it is expressive in this case.

Maybe you should go for a ratio: Error.message.length / code.length.

Related: http://codegolf.stackexchange.com/questions/5802/write-the-shortest-program-that-generates-the-most-compiler-warnings-and-errors

Template error messages are fun to decipher. Consider this:
#include <vector>
#include <algorithm>
int main()
{
    int a;
    std::vector< std::vector <int> > v;
    std::vector< std::vector <int> >::const_iterator it = std::find( v.begin(), v.end(), a );
}

Compiling with gcc -c error.cpp (4.6.3) will produce 15786 bytes of output, with a longest line of 330 characters.

In file included from /usr/include/c++/4.6/algorithm:63:0,
                 from error_code.cpp:2:
/usr/include/c++/4.6/bits/stl_algo.h: In function ‘_RandomAccessIterator std::__find(_RandomAccessIterator, _RandomAccessIterator, const _Tp&, std::random_access_iterator_tag) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator*, std::vector > >, _Tp = int]’:
/usr/include/c++/4.6/bits/stl_algo.h:4403:45:   instantiated from ‘_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = __gnu_cxx::__normal_iterator*, std::vector > >, _Tp = int]’
error_code.cpp:8:89:   instantiated from here
/usr/include/c++/4.6/bits/stl_algo.h:162:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’
/usr/include/c++/4.6/bits/stl_algo.h:162:4: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)
/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)
/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)
/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_algo.h:4403:45:   instantiated from ‘_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = __gnu_cxx::__normal_iterator*, std::vector > >, _Tp = int]’
error_code.cpp:8:89:   instantiated from here
/usr/include/c++/4.6/bits/stl_algo.h:166:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’
/usr/include/c++/4.6/bits/stl_algo.h:166:4: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)
/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)
/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)
/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_algo.h:170:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’
/usr/include/c++/4.6/bits/stl_algo.h:170:4: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)
/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)
/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)
/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_algo.h:174:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’
/usr/include/c++/4.6/bits/stl_algo.h:174:4: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)
/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)
/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)
/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_algo.h:182:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’
/usr/include/c++/4.6/bits/stl_algo.h:182:4: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)
/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)
/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)
/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_algo.h:186:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’
/usr/include/c++/4.6/bits/stl_algo.h:186:4: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)
/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)
/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)
/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_algo.h:190:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’
/usr/include/c++/4.6/bits/stl_algo.h:190:4: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)
/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)
/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)
/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)
/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)
/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)

Edit 2016-04-29: gcc 5.3.0 got it a bit better: only 9300 bytes, longest line is 361 characters long...
Edit 2019-04-04: gcc 6.5.0: 11237 bytes, but gives some hints on the error, as in theses lines:

error.cpp:7:92:   required from here
/usr/include/c++/6/bits/predefined_ops.h:199:17: error: no match for ‘operator==’ (operand types are ‘std::vector’ and ‘const int’)
  { return *__it == _M_value; }
           ~~~~~~^~~~~~~~~~~

Edit 2022-01-06: gcc 7.5.0 (Ubuntu 18.04): 11405 bytes, still no real clue on what happens, unfortunately (which could be something like, say, erroneous type 'int' as arg 3 for std::find(), expected type: 'std::vector<int>' ).
Oh, BTW, ratio error/code can even be increased by removing unnecessary stuff:
int main()
{
    int a;
    std::vector< std::vector <int> > v;
    std::find( v.begin(), v.end(), a );
}

19 characters
Create a file a.cpp with this content :
#include __FILE__
p;

Compile as :
g++ a.cpp

and get amazing 21300 lines error messages  :
In file included from a.cpp:1:0,
                 from a.cpp:1,
                 from a.cpp:1,
                 from a.cpp:1,

...
... 21280 error lines ...
...
In file included from a.cpp:1:0,
                 from a.cpp:1,
                 from a.cpp:1,
                 from a.cpp:1,
                 from a.cpp:1:
a.cpp:2:1: error: ‘p’ does not name a type
In file included from a.cpp:1:0,
                 from a.cpp:1,
                 from a.cpp:1,
                 from a.cpp:1:
a.cpp:2:1: error: ‘p’ does not name a type
In file included from a.cpp:1:0,
                 from a.cpp:1,
                 from a.cpp:1:
a.cpp:2:1: error: ‘p’ does not name a type
In file included from a.cpp:1:0,
                 from a.cpp:1:
a.cpp:2:1: error: ‘p’ does not name a type
In file included from a.cpp:1:0:
a.cpp:2:1: error: ‘p’ does not name a type
a.cpp:2:1: error: ‘p’ does not name a type

+1. Judge's favorite. Didn't think about this particular abuse.

Hm. What about #include __FILE__ and a very long filename..?

@AKX Right. Thanks. Reduced by 4 characters :)

Why does this do that? I'm curious now.

@Rob it includes the same file over and over, and it redefines main every time.

Oh, I get it! That's sneaky!

I get more error output by replacing a(); with *; and it's shorter too.

Upvote because no boring templates there :)

On my Windows machine, Clang produces even longer output, upwards of 8 MB (!!!) when compiled with clang++ -ferrorlimit=1000 a.cpp. The longest line is 466 characters long.

-fmax-include-depth=100000000000 ... I started the compilation back in 2011 and it's still going.

Based on a message length / code length ratio, this may be the best solution:

Message (81):
code: file not recognized: File truncated
collect2: ld returned 1 exit status

81 / 0 = Inf

+1 Clever way, best ratio! But not longer message...

The message is actually 81 bytes. Not that it matters, but just an FYI

98 (necessary) characters:
template<class T>struct W{T v;W(T v):v(v){}};
template<class T>int f(T x){f(W<T>(x));}
main(){f(0);}

Produces the following error output in GCC (4.4.5):
golf.cpp: In function ‘int f(T) [with T = W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<int> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >]’:
golf.cpp:2: error: template instantiation depth exceeds maximum of 500 (use -ftemplate-depth-NN to increase the maximum) instantiating ‘struct W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<int> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<int> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<int> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >]’

... snip ...

golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<W<W<W<W<W<W<W<W<int> > > > > > > > > > > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<W<W<W<W<W<W<W<int> > > > > > > > > > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<W<W<W<W<W<W<int> > > > > > > > > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<W<W<W<W<W<int> > > > > > > > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<W<W<W<W<int> > > > > > > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<W<W<W<int> > > > > > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<W<W<int> > > > > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<W<int> > > > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<W<int> > > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<W<int> > >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<W<int> >]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = W<int>]’
golf.cpp:2:   instantiated from ‘int f(T) [with T = int]’
golf.cpp:3:   instantiated from here

golf.cpp:2: error: invalid use of incomplete type ‘struct W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<int> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >’
golf.cpp:1: error: declaration of ‘struct W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<int> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >’

Statistics:
$ g++ golf.cpp 2>&1 | wc -c
537854
$ clang golf.cpp 2>&1 | wc -c
22666
$ g++ -ftemplate-depth-10000 golf.cpp 2>&1 | wc -c # 268+ MB of RAM and almost 15 minutes
200750356

Ungolfed (produces longer output):
template<class T>
struct Wrap {
    T value;
    Wrap(T v) : value(v) {}
};

template<class T>
void func(T x)
{
    func(Wrap<T>(x));
}

int main(void)
{
    func(0);
    return 0;
}

I discovered this when I wanted to see if C++ supports polymorphic recursion (and, as you can clearly see, it doesn't).  Here's a trivial example of polymorphic recursion in Haskell:
Prelude> let f :: (Show a) => a -> String; f x = show x ++ " " ++ f [x]
Prelude> f 0
"0 [0] [[0]] [[[0]]] [[[[0]]]] [[[[[0]]]]] [[[[[[0]]]]]] [[[[[[[0]]]]]]] [[[[[[[[0]] ...

Here, this requires Haskell to act like it instantiates Show x, Show [x], Show [[x]], Show [[[x]]], ad infinitum.  Haskell does it by turning (Show x) => into an implicit parameter to the function f added by the compiler, something like this:
type Show a = a -> String

showList :: Show a -> [a] -> String
showList show []     = "[]"
showList show (x:xs) = '[' : show x ++ showItems xs where
    showItems []     = "]"
    showItems (x:xs) = ',' : show x ++ showItems xs

f :: Show a -> a -> String
f show x = show x ++ " " ++ f (showList show) [x]

C++ does it by literally trying to construct such instances until the template instantiation depth is exceeded.

Inflated to 102 bytes (cl doesn't like implicit int in C++ mode) it generates 14.380.923 bytes of error output after 4½ minutes of CPU time and a peak of about 100 MiB of memory usage.

Could you explain what have you tried to achieve with polymorphic recursion? Because in an example both in Haskell, and in C++ the process is infinite, only difference is it occurs in run or compile time.

@sukhmel No, because Haskell is lazy, it will compile and run (as demo'd)

@cat I haven't implied it will not run, I pointed out that such a run will never stop, or will it? Althoug I suppose that in what Joey tried to achieve there should have been stop condition in case of specific template, that's why I was wondering for what was the idea behind trying polymorphic recursion.

Is that a... bomb?

279 chars
#define A(s) s##s##s##s##s##s##s##s
#define B(s) A(s##s##s##s##s##s##s##s)
#define C(s) B(s##s##s##s##s##s##s##s)
#define D(s) C(s##s##s##s##s##s##s##s)
#define E(s) D(s##s##s##s##s##s##s##s)
#define F(s) E(s##s##s##s##s##s##s##s)
#define G(s) F(s##s##s##s##s##s##s##s)
a G(foo)

With gcc 4.2.1, generates the error error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘foofoo....foofoo’ with 2^21 copies of foo.  6,291,558 bytes in all.  It's about as big an identifier as I can get, replacing foo with food generates an ICE.

Read the instructions! You should generate a single long error, not many short errors.

@Elazar: OK, fixed.

gcc 4.4.5 segfaults.  Win!

@JoeyAdams: Please report this as a bug than

@the_drow It's a feature.

@muntoo: How come? An ICE is never a good idea.

Not really a big deal - gcc tries to allocate too much space on the stack. Using ulimit -s unlimited prevents the crash. Adding another seven layers of macros I can get it to die with virtual memory exhausted.

A pattern like this will get you further: #define A(s) s##s##s##s #define B(s) A(s) #define C(s) B(B(B(s))) #define D(s) C(C(C(s))) D(foo). This gets me an error message about as long with much less code, and grows much faster with increasing the pattern in any dimension, since we are essentially implementing the Ackermann function.

The following code is based on an actual error I once encountered.
template <int i>
void bar();

template <int i>
void foo()
{
    bar<i>();
    char baz[i];
}

template <int i>
void bar()
{
    foo<i-1>();
}

int main(void)
{
    foo<2000>();

    return 0;
}

(using gcc)
Pretty obvious template recursion, but since I used ftemplate-depth=100000 for this run this doesn't produce an error. The real source of the error messages comes from char baz[i];, which produces an error when i drops to -1.
After about half an hour, I'm sitting on 21,000 compiler errors, 300,000 lines of error messages, and 280 megabytes of RAM used by the compiler. And it's showing no signs of stopping.
EDIT:
One hour later, now at 36,000 compiler errors, 504,000 lines of error messages, and 480 megabytes of RAM... and still going.
EDIT #2:
About half an hour later:
ccplus1.exe has stopped working

Final statistics: 38,876 compiler errors, 544,624 lines of error messages, totaling 48.8 megabytes of data, and 518.9 megabytes of RAM used by the compiler before it crashed.

I'm sure none of those error messages even point to the real issue... which is typical of the average STL typo.

This is terrifying. I've let this keep running for only a few minutes and I'm sitting on 10GB of error messages (160 million lines). Note that I had to compile with g++-10 -ftemplate-depth=1000000 -ftemplate-backtrace-limit=0 a.cpp -o a 2> err.txt

It's maybe 20 minutes later, and now it's at 35GB. I have to stop this before it crashes my computer XD

28 bytes
Sabotaging the standard library:
#define std +
#include<map>

Using clang on OS X 10.9:
c++ foo.cpp -o foo -ferror-limit=-1
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:422:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__config:347:11: error: expected identifier or '{'
namespace std {
          ^
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:422:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__config:347:11: error: expected external declaration
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:422:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__config:347:15: error: expected unqualified-id
namespace std {
              ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:423:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__tree:15:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/iterator:330:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/type_traits:203:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/cstddef:50:1: error: expected identifier or '{'
_LIBCPP_BEGIN_NAMESPACE_STD
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__config:343:47: note: expanded from macro '_LIBCPP_BEGIN_NAMESPACE_STD'
#define _LIBCPP_BEGIN_NAMESPACE_STD namespace std {inline namespace _LIBCPP_NAMESPACE {
                                              ^
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:423:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__tree:15:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/iterator:330:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/type_traits:203:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/cstddef:50:1: error: expected external declaration
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__config:343:47: note: expanded from macro '_LIBCPP_BEGIN_NAMESPACE_STD'
#define _LIBCPP_BEGIN_NAMESPACE_STD namespace std {inline namespace _LIBCPP_NAMESPACE {
                                              ^
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:423:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__tree:15:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/iterator:330:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/type_traits:203:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/cstddef:50:1: error: expected unqualified-id

[[SNIP...]]

_LIBCPP_NEW_DELETE_VIS void* operator new(std::size_t __sz)
                             ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:132:43: error: expected parameter declarator
_LIBCPP_NEW_DELETE_VIS void* operator new(std::size_t __sz, const std::nothrow_t&) _NOEXCEPT _NOALIAS;
                                          ^
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:423:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__tree:16:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/memory:597:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:132:43: error: expected ')'
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:132:42: note: to match this '('
_LIBCPP_NEW_DELETE_VIS void* operator new(std::size_t __sz, const std::nothrow_t&) _NOEXCEPT _NOALIAS;
                                         ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:134:63: error: C++ requires a type specifier for all declarations
_LIBCPP_NEW_DELETE_VIS void  operator delete(void* __p, const std::nothrow_t&) _NOEXCEPT;
                                                        ~~~~~ ^
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:423:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__tree:16:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/memory:597:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:134:63: error: expected ')'
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:134:45: note: to match this '('
_LIBCPP_NEW_DELETE_VIS void  operator delete(void* __p, const std::nothrow_t&) _NOEXCEPT;
                                            ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:136:45: error: expected parameter declarator
_LIBCPP_NEW_DELETE_VIS void* operator new[](std::size_t __sz)
                                            ^
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:423:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__tree:16:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/memory:597:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:136:45: error: expected ')'
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:136:44: note: to match this '('
_LIBCPP_NEW_DELETE_VIS void* operator new[](std::size_t __sz)
                                           ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:138:11: error: expected a type
    throw(std::bad_alloc)
          ^
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:423:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__tree:16:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/memory:597:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:138:11: error: expected ')'
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:138:10: note: to match this '('
    throw(std::bad_alloc)
         ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:136:30: error: 'operator new[]' must have at least one parameter
_LIBCPP_NEW_DELETE_VIS void* operator new[](std::size_t __sz)
                             ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:141:45: error: expected parameter declarator
_LIBCPP_NEW_DELETE_VIS void* operator new[](std::size_t __sz, const std::nothrow_t&) _NOEXCEPT _NOALIAS;
                                            ^
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:423:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__tree:16:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/memory:597:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:141:45: error: expected ')'
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:141:44: note: to match this '('
_LIBCPP_NEW_DELETE_VIS void* operator new[](std::size_t __sz, const std::nothrow_t&) _NOEXCEPT _NOALIAS;
                                           ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:143:65: error: C++ requires a type specifier for all declarations
_LIBCPP_NEW_DELETE_VIS void  operator delete[](void* __p, const std::nothrow_t&) _NOEXCEPT;
                                                          ~~~~~ ^
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:423:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__tree:16:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/memory:597:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:143:65: error: expected ')'
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:143:47: note: to match this '('
_LIBCPP_NEW_DELETE_VIS void  operator delete[](void* __p, const std::nothrow_t&) _NOEXCEPT;
                                              ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:145:55: error: expected parameter declarator
inline _LIBCPP_INLINE_VISIBILITY void* operator new  (std::size_t, void* __p) _NOEXCEPT {return __p;}
                                                      ^
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
In file included from foo.cpp:2:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:423:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/__tree:16:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/memory:597:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:145:55: error: expected ')'
foo.cpp:1:13: note: expanded from macro 'std'
#define std +
            ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:145:54: note: to match this '('
inline _LIBCPP_INLINE_VISIBILITY void* operator new  (std::size_t, void* __p) _NOEXCEPT {return __p;}
                                                     ^
Stack dump:
0.  Program arguments: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -cc1 -triple x86_64-apple-macosx10.9.0 -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name foo.cpp -mrelocation-model pic -pic-level 2 -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 236.3 -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/5.1 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk -stdlib=libc++ -fdeprecated-macro -fdebug-compilation-dir /tmp -ferror-limit -1 -fmessage-length 203 -stack-protector 1 -mstackrealign -fblocks -fobjc-runtime=macosx-10.9.0 -fencode-extended-block-signature -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -vectorize-slp -o /var/folders/gf/l1sssgds0b30z21wn2n4p3rm0000gr/T/foo-19eda8.o -x c++ foo.cpp
1.  /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/new:145:89: current parser token '{'
clang: error: unable to execute command: Segmentation fault: 11
clang: error: clang frontend command failed due to signal (use -v to see invocation)
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.2.0
Thread model: posix
clang: note: diagnostic msg: PLEASE submit a bug report to http://developer.apple.com/bugreporter/ and include the crash backtrace, preprocessed source, and associated run script.
clang: error: unable to execute command: Segmentation fault: 11
clang: note: diagnostic msg: Error generating preprocessed source(s).

456 lines of errors, 50 errors, and a compiler segfault!
Clang version:
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.2.0
Thread model: posix

did you send in a bug report for that segfault?

With my current LLVM version (Apple LLVM version 8.0.0 (clang-800.0.42.1)), I no longer get the segfault. Not sure if I should still submit anything - doubtful the LLVM maintainers will care about an old bug.

Similar to VJo:
a.cpp:
int main() { return
#include "a.cpp"
#include "a.cpp"
}

g++ a.cpp
produces a lot of output (at least 2 gigabytes before I killed it)

C++
Based on BЈовић's solution:
File: golf.cpp:
#include "golf.cpp"
#include "golf.cpp"

Running this under G++ will not finish, however, I have computed the length of the error it will eventually emit as roughly 85*2^140 terabytes.

I stumbled across this by accident:
#include<functional>
#include<algorithm>
#include<array>
#include<stdexcept>

int main(int argc,char** argv){
    std::array<double, 3> arr;

    arr[0] = 0; arr[1] = 1; arr[2] = 1;

    if (std::any_of(arr.begin(), arr.end(),
                    std::bind(std::less_equal<double>(), std::placeholders::_2, 0))){
        throw std::invalid_argument("Geometry with bin width less or equal to zero");
    }
}

On c++x11 it produces 44kb of error messages, in which compiler tries to say: Please define placeholder for first argument if you define it for second.
See it on ideone.

I'm terrified of making a typo in a C++ program that uses the STL...

+1 for a answer that is an actual real life example.

Forgetting a semi-colon before an include statement
int i
#include <stdio.h>

I made this error in a header file which I had included in throughout most of my project before the standard libraries. It churned for over 10 minutes and generated about 1000 separate error messages.

C++11 variadic templates (69 characters)
template<int... p>
void f()
{
    return f<0,p...>();
}

int main() {
    f();
}

Configuring maximum template instantation depth you could set the length of the error. Here is an example using GCC 4.8.1 with default template depth (900):

prog.cpp:4:22: error: template instantiation depth exceeds maximum of
  900 (use -ftemplate-depth= to increase the maximum) substituting
  ‘template void f() [with int ...p = {0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}]’
       return f<0,p...>();
                        ^ prog.cpp:4:22:   recursively required from ‘void f() [with int ...p = {0}]’ prog.cpp:4:22:   required from ‘void
  f() [with int ...p = {}]’ prog.cpp:8:4:   required from here
prog.cpp:4:22: error: no matching function for call to ‘f()’
  prog.cpp:4:22: note: candidate is: prog.cpp:2:6: note: template void f()  void f()
        ^ prog.cpp:2:6: note:   substitution of deduced template arguments resulted in errors seen above prog.cpp:4:22: error:
  return-statement with a value, in function returning 'void'
  [-fpermissive]
       return f<0,p...>();
                        ^

Also you could add ten more characters and use unsigned integer underflow to increase the length of the error:
template<unsigned int... p>
void f()
{
    return f<0-1,p...>();
}

int main() {
    f();
}

prog.cpp:4:24: error: template instantiation depth exceeds maximum of
  900 (use -ftemplate-depth= to increase the maximum) substituting
  ‘template void f() [with unsigned int ...p =
  {4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u,
  4294967295u, 4294967295u, 4294967295u, 4294967295u, 4294967295u}]’
       return f<0-1,p...>();
                          ^ prog.cpp:4:24:   recursively required from ‘void f() [with unsigned int ...p = {4294967295u}]’ prog.cpp:4:24:
  required from ‘void f() [with unsigned int ...p = {}]’ prog.cpp:8:4:
  required from here
prog.cpp:4:24: error: no matching function for call to ‘f()’
  prog.cpp:4:24: note: candidate is: prog.cpp:2:6: note:
  template void f()  void f()
        ^ prog.cpp:2:6: note:   substitution of deduced template arguments resulted in errors seen above prog.cpp:4:24: error:
  return-statement with a value, in function returning 'void'
  [-fpermissive]
       return f<0-1,p...>();
                  ^

Here is an example running at ideone.

82 bytes: This one works similar to Joey Adams' approach, but the error message will grow exponentially with respect to -ftemplate-depth (because std::set<T> is actually std::set<T, std::less<T>, std::allocator<T>>).
For (x = -ftemplate-depth) >= 28, there will be 1460×3x-27 + 269x - 5381 bytes of error messages (compiled by gcc 7.2.0). That is, in default settings (x=900), it will output about 4.9×10419 bytes of error message theoretically.
Note that without the return statement, the error messages will only produced at the end of the compiling. (so in default settings you won't get the messages - you will run out of memory first.)
Warning: Compiling this program will consume lots of memory.
#include<set>
template<class T>T f(T a){return f(std::set<T>());}int main(){f(0);}

Try it online!

Using map seems strictly more evil, since std::map<T,T> is std::map<T,T,std::less<T>,std::allocator<std::pair<T,T>>> so you get 5-way recursion instead of 3, for only 2 more bytes.

Also, verified on LLVM version 10.0.0 (clang-1000.11.45.5), with no extra flags. Generated 148,379 bytes at -ftemplate-depth=13, 423,572 bytes at -ftemplate-depth=14, and 1,247,322 bytes at -ftemplate-depth=15. map variant generates 13,373,990 bytes at depth 14 and 66,759,871 bytes at depth 15.

Egads, the default on Clang is -ftemplate-depth=1024, which means somewhere north of 10^713 bytes with the map variant. I believe this means you win...

This produces infinite output on GCC 5.2 and Clang 3.6 (on Clang requires -ferror-limit=0, on GCC works with default settings):
#include __FILE__
#include __FILE__

A file named a.cpp. Code:
main(){
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
#include "a.cpp"
}

This is a fork bomb where n=40.

This produces 21KB of output for me with GCC 10.1.0:
#include <iostream>
int main() { std::cin >> ""; }

Output:
error.cpp: In function ‘int main()’:
error.cpp:2:23: error: no match for ‘operator>>’ (operand types are ‘std::istream’ {aka ‘std::basic_istream<char>’} and ‘const char [1]’)
    2 | int main() { std::cin >> ""; }
      |              ~~~~~~~~ ^~ ~~
      |                   |      |
      |                   |      const char [1]
      |                   std::istream {aka std::basic_istream<char>}
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:168:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ (near match)
  168 |       operator>>(bool& __n)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:168:7: note:   conversion of argument 1 would be ill-formed:
error.cpp:2:26: error: cannot bind non-const lvalue reference of type ‘bool&’ to an rvalue of type ‘bool’
    2 | int main() { std::cin >> ""; }
      |                          ^~
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:172:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char; _Traits = std::char_traits<char>]’ (near match)
  172 |       operator>>(short& __n);
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:172:7: note:   conversion of argument 1 would be ill-formed:
error.cpp:2:26: error: invalid conversion from ‘const char*’ to ‘short int’ [-fpermissive]
    2 | int main() { std::cin >> ""; }
      |                          ^~
      |                          |
      |                          const char*
error.cpp:2:26: error: cannot bind rvalue ‘(short int)((const char*)"")’ to ‘short int&’
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:175:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ (near match)
  175 |       operator>>(unsigned short& __n)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:175:7: note:   conversion of argument 1 would be ill-formed:
error.cpp:2:26: error: invalid conversion from ‘const char*’ to ‘short unsigned int’ [-fpermissive]
    2 | int main() { std::cin >> ""; }
      |                          ^~
      |                          |
      |                          const char*
error.cpp:2:26: error: cannot bind rvalue ‘(short unsigned int)((const char*)"")’ to ‘short unsigned int&’
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:179:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char; _Traits = std::char_traits<char>]’ (near match)
  179 |       operator>>(int& __n);
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:179:7: note:   conversion of argument 1 would be ill-formed:
error.cpp:2:26: error: invalid conversion from ‘const char*’ to ‘int’ [-fpermissive]
    2 | int main() { std::cin >> ""; }
      |                          ^~
      |                          |
      |                          const char*
error.cpp:2:26: error: cannot bind rvalue ‘(int)((const char*)"")’ to ‘int&’
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:182:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ (near match)
  182 |       operator>>(unsigned int& __n)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:182:7: note:   conversion of argument 1 would be ill-formed:
error.cpp:2:26: error: invalid conversion from ‘const char*’ to ‘unsigned int’ [-fpermissive]
    2 | int main() { std::cin >> ""; }
      |                          ^~
      |                          |
      |                          const char*
error.cpp:2:26: error: cannot bind rvalue ‘(unsigned int)((const char*)"")’ to ‘unsigned int&’
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:186:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ (near match)
  186 |       operator>>(long& __n)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:186:7: note:   conversion of argument 1 would be ill-formed:
error.cpp:2:26: error: invalid conversion from ‘const char*’ to ‘long int’ [-fpermissive]
    2 | int main() { std::cin >> ""; }
      |                          ^~
      |                          |
      |                          const char*
error.cpp:2:26: error: cannot bind rvalue ‘(long int)((const char*)"")’ to ‘long int&’
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:190:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ (near match)
  190 |       operator>>(unsigned long& __n)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:190:7: note:   conversion of argument 1 would be ill-formed:
error.cpp:2:26: error: invalid conversion from ‘const char*’ to ‘long unsigned int’ [-fpermissive]
    2 | int main() { std::cin >> ""; }
      |                          ^~
      |                          |
      |                          const char*
error.cpp:2:26: error: cannot bind rvalue ‘(long unsigned int)((const char*)"")’ to ‘long unsigned int&’
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:195:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ (near match)
  195 |       operator>>(long long& __n)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:195:7: note:   conversion of argument 1 would be ill-formed:
error.cpp:2:26: error: invalid conversion from ‘const char*’ to ‘long long int’ [-fpermissive]
    2 | int main() { std::cin >> ""; }
      |                          ^~
      |                          |
      |                          const char*
error.cpp:2:26: error: cannot bind rvalue ‘(long long int)((const char*)"")’ to ‘long long int&’
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:199:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ (near match)
  199 |       operator>>(unsigned long long& __n)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:199:7: note:   conversion of argument 1 would be ill-formed:
error.cpp:2:26: error: invalid conversion from ‘const char*’ to ‘long long unsigned int’ [-fpermissive]
    2 | int main() { std::cin >> ""; }
      |                          ^~
      |                          |
      |                          const char*
error.cpp:2:26: error: cannot bind rvalue ‘(long long unsigned int)((const char*)"")’ to ‘long long unsigned int&’
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:235:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ (near match)
  235 |       operator>>(void*& __p)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:235:7: note:   conversion of argument 1 would be ill-formed:
error.cpp:2:26: error: invalid conversion from ‘const void*’ to ‘void*’ [-fpermissive]
    2 | int main() { std::cin >> ""; }
      |                          ^~
      |                          |
      |                          const void*
error.cpp:2:26: error: cannot bind rvalue ‘(void*)((const void*)((const char*)""))’ to ‘void*&’
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:120:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__istream_type& (*)(std::basic_istream<_CharT, _Traits>::__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
  120 |       operator>>(__istream_type& (*__pf)(__istream_type&))
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:120:36: note:   no known conversion for argument 1 from ‘const char [1]’ to ‘std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&)’ {aka ‘std::basic_istream<char>& (*)(std::basic_istream<char>&)’}
  120 |       operator>>(__istream_type& (*__pf)(__istream_type&))
      |                  ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/10.1.0/istream:124:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__ios_type& (*)(std::basic_istream<_CharT, _Traits>::__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>; std::basic_istream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]’
  124 |       operator>>(__ios_type& (*__pf)(__ios_type&))
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:124:32: note:   no known conversion for argument 1 from ‘const char [1]’ to ‘std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&)’ {aka ‘std::basic_ios<char>& (*)(std::basic_ios<char>&)’}
  124 |       operator>>(__ios_type& (*__pf)(__ios_type&))
      |                  ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
/usr/include/c++/10.1.0/istream:131:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
  131 |       operator>>(ios_base& (*__pf)(ios_base&))
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:131:30: note:   no known conversion for argument 1 from ‘const char [1]’ to ‘std::ios_base& (*)(std::ios_base&)’
  131 |       operator>>(ios_base& (*__pf)(ios_base&))
      |                  ~~~~~~~~~~~~^~~~~~~~~~~~~~~~
/usr/include/c++/10.1.0/istream:214:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(float&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
  214 |       operator>>(float& __f)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:214:25: note:   no known conversion for argument 1 from ‘const char [1]’ to ‘float&’
  214 |       operator>>(float& __f)
      |                  ~~~~~~~^~~
/usr/include/c++/10.1.0/istream:218:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(double&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
  218 |       operator>>(double& __f)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:218:26: note:   no known conversion for argument 1 from ‘const char [1]’ to ‘double&’
  218 |       operator>>(double& __f)
      |                  ~~~~~~~~^~~
/usr/include/c++/10.1.0/istream:222:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long double&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
  222 |       operator>>(long double& __f)
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:222:31: note:   no known conversion for argument 1 from ‘const char [1]’ to ‘long double&’
  222 |       operator>>(long double& __f)
      |                  ~~~~~~~~~~~~~^~~
/usr/include/c++/10.1.0/istream:259:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]’
  259 |       operator>>(__streambuf_type* __sb);
      |       ^~~~~~~~
/usr/include/c++/10.1.0/istream:259:36: note:   no known conversion for argument 1 from ‘const char [1]’ to ‘std::basic_istream<char>::__streambuf_type*’ {aka ‘std::basic_streambuf<char>*’}
  259 |       operator>>(__streambuf_type* __sb);
      |                  ~~~~~~~~~~~~~~~~~~^~~~
In file included from /usr/include/c++/10.1.0/string:56,
                 from /usr/include/c++/10.1.0/bits/locale_classes.h:40,
                 from /usr/include/c++/10.1.0/bits/ios_base.h:41,
                 from /usr/include/c++/10.1.0/ios:42,
                 from /usr/include/c++/10.1.0/ostream:38,
                 from /usr/include/c++/10.1.0/iostream:39,
                 from error.cpp:1:
/usr/include/c++/10.1.0/bits/basic_string.tcc:1476:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)’
 1476 |     operator>>(basic_istream<_CharT, _Traits>& __in,
      |     ^~~~~~~~
/usr/include/c++/10.1.0/bits/basic_string.tcc:1476:5: note:   template argument deduction/substitution failed:
error.cpp:2:26: note:   mismatched types ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’ and ‘const char [1]’
    2 | int main() { std::cin >> ""; }
      |                          ^~
In file included from /usr/include/c++/10.1.0/istream:991,
                 from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/bits/istream.tcc:931:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT&)’
  931 |     operator>>(basic_istream<_CharT, _Traits>& __in, _CharT& __c)
      |     ^~~~~~~~
/usr/include/c++/10.1.0/bits/istream.tcc:931:5: note:   template argument deduction/substitution failed:
error.cpp:2:26: note:   deduced conflicting types for parameter ‘_CharT’ (‘char’ and ‘const char [1]’)
    2 | int main() { std::cin >> ""; }
      |                          ^~
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:756:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char&)’
  756 |     operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
      |     ^~~~~~~~
/usr/include/c++/10.1.0/istream:756:5: note:   template argument deduction/substitution failed:
error.cpp:2:26: note:   cannot convert ‘""’ (type ‘const char [1]’) to type ‘unsigned char&’
    2 | int main() { std::cin >> ""; }
      |                          ^~
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:761:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char&)’
  761 |     operator>>(basic_istream<char, _Traits>& __in, signed char& __c)
      |     ^~~~~~~~
/usr/include/c++/10.1.0/istream:761:5: note:   template argument deduction/substitution failed:
error.cpp:2:26: note:   cannot convert ‘""’ (type ‘const char [1]’) to type ‘signed char&’
    2 | int main() { std::cin >> ""; }
      |                          ^~
In file included from /usr/include/c++/10.1.0/istream:991,
                 from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/bits/istream.tcc:963:5: note: candidate: ‘template<class _CharT2, class _Traits2> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT2*)’
  963 |     operator>>(basic_istream<_CharT, _Traits>& __in, _CharT* __s)
      |     ^~~~~~~~
/usr/include/c++/10.1.0/bits/istream.tcc:963:5: note:   template argument deduction/substitution failed:
error.cpp:2:26: note:   deduced conflicting types for parameter ‘_CharT2’ (‘char’ and ‘const char’)
    2 | int main() { std::cin >> ""; }
      |                          ^~
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:803:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char*)’
  803 |     operator>>(basic_istream<char, _Traits>& __in, unsigned char* __s)
      |     ^~~~~~~~
/usr/include/c++/10.1.0/istream:803:5: note:   template argument deduction/substitution failed:
error.cpp:2:26: note:   cannot convert ‘""’ (type ‘const char [1]’) to type ‘unsigned char*’
    2 | int main() { std::cin >> ""; }
      |                          ^~
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:808:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char*)’
  808 |     operator>>(basic_istream<char, _Traits>& __in, signed char* __s)
      |     ^~~~~~~~
/usr/include/c++/10.1.0/istream:808:5: note:   template argument deduction/substitution failed:
error.cpp:2:26: note:   cannot convert ‘""’ (type ‘const char [1]’) to type ‘signed char*’
    2 | int main() { std::cin >> ""; }
      |                          ^~
In file included from /usr/include/c++/10.1.0/iostream:40,
                 from error.cpp:1:
/usr/include/c++/10.1.0/istream:980:5: note: candidate: ‘template<class _Istream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_istream<_Istream>, std::__is_extractable<typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type, _Tp&&, void> >::value, typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type>::type std::operator>>(_Istream&&, _Tp&&)’
  980 |     operator>>(_Istream&& __is, _Tp&& __x)
      |     ^~~~~~~~
/usr/include/c++/10.1.0/istream:980:5: note:   template argument deduction/substitution failed:
/usr/include/c++/10.1.0/istream: In substitution of ‘template<class _Istream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_istream<_Istream>, std::__is_extractable<typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type, _Tp&&, void> >::value, typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type>::type std::operator>>(_Istream&&, _Tp&&) [with _Istream = std::basic_istream<char>&; _Tp = const char (&)[1]]’:
error.cpp:2:26:   required from here
/usr/include/c++/10.1.0/istream:980:5: error: no type named ‘type’ in ‘struct std::enable_if<false, std::basic_istream<char>&>’

At least the first error message is pretty clear

1031892 bytes / 9 bytes = ratio 114654.666667
Compiler g++-11, with -std=c++20 flag
p<p<p<p<p

produces 1031892 bytes, or 21056 lines of error.
first 20 lines look like this:
test.cpp:1:9: error: ‘p’ was not declared in this scope
    1 | p<p<p<p<p
      |         ^
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:7: error: ‘p’ was not declared in this scope
    1 | p<p<p<p<p
      |       ^
test.cpp:1:9: error: ‘p’ was not declared in this scope
    1 | p<p<p<p<p
      |         ^
test.cpp:1:9: error: ‘p’ was not declared in this scope

and last 20 lines:
      |         ^
test.cpp:1:5: error: ‘p’ was not declared in this scope
    1 | p<p<p<p<p
      |     ^
test.cpp:1:9: error: ‘p’ was not declared in this scope
    1 | p<p<p<p<p
      |         ^
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:9: error: ‘p’ was not declared in this scope
test.cpp:1:7: error: ‘p’ was not declared in this scope
    1 | p<p<p<p<p
      |       ^
test.cpp:1:9: error: ‘p’ was not declared in this scope
    1 | p<p<p<p<p
      |         ^
test.cpp:1:1: error: ‘p’ does not name a type
    1 | p<p<p<p<p
      | ^

And my compiler version:
$ g++-11 --version
g++-11 (Ubuntu 11.1.0-1ubuntu1~18.04.1) 11.1.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

What if I add more "<p" ?

1 byte -> 70 bytes error, ratio = 70
$ echo 'p' > test.cpp; g++-11 test.cpp -o test -std=c++20 2>&1 | wc -c
70

3 byte -> 636 bytes error, ratio = 212
$ echo 'p<p' > test.cpp; g++-11 test.cpp -o test -std=c++20 2>&1 | wc -c
636

5 byte -> 7608 bytes error, ratio = 1521.6
$ echo 'p<p<p' > test.cpp; g++-11 test.cpp -o test -std=c++20 2>&1 | wc -c
7608

7 byte -> 88884 bytes error, ratio = 12697.7142857
$ echo 'p<p<p<p' > test.cpp; g++-11 test.cpp -o test -std=c++20 2>&1 | wc -c
88884

9 byte -> 1031892 bytes error, ratio = 114654.666667
$ echo 'p<p<p<p<p' > test.cpp; g++-11 test.cpp -o test -std=c++20 2>&1 | wc -c
1031892

11 byte -> 12132840 bytes error, ratio = 1102985.45455
$ echo 'p<p<p<p<p<p' > test.cpp; g++-11 test.cpp -o test -std=c++20 2>&1 | wc -c
12132840

...and latter take too much time to evaluate.

Wow, this one really takes the cake! 21k lines of absolutely repetitive garbage. Do you know why this happens exactly? It doesn't seem to happen with C++17, there it just says error: ‘p’ does not name a type. So something changed with C++20, and it definitely changed for the worse. Could this even be a bug? Hopefully it isn't a feature...

19 bytes
... you need to get at least a few megabytes of errors (if you have bash under /bin/bash, untested with env)
#include</bin/bash>

under Windows 7 (/w Cygwin) in results i got 762140 lines of errors (~73 MiB, pic related)
In file included from owo.cpp:1:
/bin/bash:1:3: error: stray ‘\220’ in program
    1 | MZ�       ��  �       @                                   �   � �  �!�L�!This program cannot be run in DOS mode.
      |   ^
/bin/bash:1:4: warning: null character(s) ignored
    1 | MZ�       ��  �       @                                   �   � �  �!�L�!This program cannot be run in DOS mode.
      |    ^
/bin/bash:1:5: error: stray ‘\3’ in program
    1 | MZ�       ��  �       @                                   �   � �  �!�L�!This program cannot be run in DOS mode.
      |     ^
/bin/bash:1:6: warning: null character(s) ignored
    1 | MZ�       ��  �       @                                   �   � �  �!�L�!This program cannot be run in DOS mode.
      |      ^
[...]
/bin/bash:2724:5: error: ‘H9’ does not name a type
 2724 |
      |     ^
/bin/bash:2725:5: error: ‘H9’ does not name a type
 2725 |     Exit Status:
      |     ^~
/bin/bash:2739:33: error: expected declaration before ‘}’ token
 2739 |       -r        read the history file and append the contents to the history
      |                                 ^
/bin/bash:2739:42: error: ‘H’ does not name a type
 2739 |       -r        read the history file and append the contents to the history
      |                                          ^
/bin/bash:2748:2: error: expected declaration before ‘}’ token
 2748 |     if HISTFILE has a value, that is used, else ~/.bash_history.
      |  ^
/bin/bash:2748:11: error: expected unqualified-id before numeric constant
 2748 |     if HISTFILE has a value, that is used, else ~/.bash_history.
      |           ^
/bin/bash:2748:54: error: expected declaration before ‘}’ token
 2748 |     if HISTFILE has a value, that is used, else ~/.bash_history.
      |                                                      ^
/bin/bash:2748:64: error: expected ‘)’ before ‘D$P’
 2748 |     if HISTFILE has a value, that is used, else ~/.bash_history.
      |                                                           ~    ^
      |                                                                )
In file included from owo.cpp:1:
/bin/bash:2750:369: error: ‘H’ does not name a type
 2750 |     If the HISTTIMEFORMAT variable is set and not null, its value is used
      |                                                                                ^
/bin/bash:2750:468: error: expected declaration before ‘}’ token
 2750 |     If the HISTTIMEFORMAT variable is set and not null, its value is used
      |                                                                                ^
/bin/bash:2750:480: error: expected class-name before ‘L’
 2750 |     If the HISTTIMEFORMAT variable is set and not null, its value is used
      |                                                                                ^
In file included from owo.cpp:1:
/bin/bash:4243:119: error: ‘E’ does not name a type
 4243 |   � d �}
      |                                                                                ^
In file included from owo.cpp:1:
/bin/bash:4243:794: error: expected declaration before ‘}’ token
 4243 |   � d �}
      |                                                                                ^
/bin/bash:4243:800: error: expected ‘)’ before ‘U’
 4243 |   � d �}
      |                                                                                ^
      |                                                                                )
In file included from owo.cpp:1:
/bin/bash:4244:237: error: expected declaration before ‘}’ token
 4244 |  p � �}
      |                                                                                ^
/bin/bash:4244:249: error: expected ‘)’ before ‘L’
 4244 |  p � �}
      |                                                                                ^
      |                                                                                )
/bin/bash:4244:385: error: expected declaration before ‘}’ token
 4244 |  p � �}
      |                                                                                ^
/bin/bash:4244:388: error: ‘I’ does not name a type
 4244 |  p � �}
      |                                                                                ^
In file included from owo.cpp:1:
/bin/bash:4246:185: error: ‘f’ does not name a type
 4246 |  p � ~
      |                                                                                ^
In file included from owo.cpp:1:
/bin/bash:7044:6: error: ‘e’ does not name a type
/bin/bash:7303:7: error: ‘T’ does not name a type
/bin/bash:7434:6: error: ‘W’ does not name a type
/bin/bash:7437:7: error: expected unqualified-id before ‘<’ token
/bin/bash:7495:10: error: ‘h’ does not name a type
/bin/bash:7529:7: error: expected declaration before ‘}’ token
/bin/bash:7530:2: error: ‘p’ does not name a type
/bin/bash:7530:3: error: expected declaration before ‘}’ token
/bin/bash:7533:10: error: expected unqualified-id before numeric constant
/bin/bash:7532:11: error: expected ‘)’ before numeric constant
In file included from owo.cpp:1:
/bin/bash:7995:245: error: expected declaration before ‘}’ token
/bin/bash:7997:3: error: expected unqualified-id before numeric constant
/bin/bash:8000:59: error: expected unqualified-id before ‘:’ token
/bin/bash:8000:66: error: ‘P’ does not name a type
/bin/bash:8000:130: error: expected unqualified-id before numeric constant
/bin/bash:8031:34: error: expected declaration before ‘}’ token
/bin/bash:8031:35: error: ‘L’ does not name a type

Can you include /bin/sh or does that point to something else?

@ceilingcat why not (but in sh case, outside Linux* - on other *nix systems output may be smaller)
\ *where sh usually is a just symlink to bash

As root, #include</dev/sda>

(22009 characters) This is something a beginner might actually run into:
Ungolfed:
#include <array>
#include <iostream>
int main() {
  std::cout << std::array{1, 2, 3};
}

Golfed:
#include <array>
#include <iostream>
main(){std::cout<<std::array{1};}

Compiled with Homebrew GCC 12.1 on MacOS 12.4, with no options.
Error:
delete.cpp:3:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
    3 | main(){std::cout<<std::array{1};}
      | ^~~~
delete.cpp: In function 'int main()':
delete.cpp:3:17: error: no match for 'operator<<' (operand types are 'std::ostream' {aka 'std::basic_ostream<char>'} and 'std::array<int, 1>')
    3 | main(){std::cout<<std::array{1};}
      |        ~~~~~~~~~^~     ~~~~~~~~
      |             |          |
      |             |          std::array<int, 1>
      |             std::ostream {aka std::basic_ostream<char>}
In file included from /opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/iostream:39,
                 from delete.cpp:2:
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:108:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(__ostream_type& (*)(__ostream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  108 |       operator<<(__ostream_type& (*__pf)(__ostream_type&))
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:108:36: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'std::basic_ostream<char>::__ostream_type& (*)(std::basic_ostream<char>::__ostream_type&)' {aka 'std::basic_ostream<char>& (*)(std::basic_ostream<char>&)'}
  108 |       operator<<(__ostream_type& (*__pf)(__ostream_type&))
      |                  ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:117:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(__ios_type& (*)(__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>; __ios_type = std::basic_ios<char>]'
  117 |       operator<<(__ios_type& (*__pf)(__ios_type&))
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:117:32: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'std::basic_ostream<char>::__ios_type& (*)(std::basic_ostream<char>::__ios_type&)' {aka 'std::basic_ios<char>& (*)(std::basic_ios<char>&)'}
  117 |       operator<<(__ios_type& (*__pf)(__ios_type&))
      |                  ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:127:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  127 |       operator<<(ios_base& (*__pf) (ios_base&))
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:127:30: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'std::ios_base& (*)(std::ios_base&)'
  127 |       operator<<(ios_base& (*__pf) (ios_base&))
      |                  ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:166:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  166 |       operator<<(long __n)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:166:23: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'long int'
  166 |       operator<<(long __n)
      |                  ~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:170:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  170 |       operator<<(unsigned long __n)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:170:32: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'long unsigned int'
  170 |       operator<<(unsigned long __n)
      |                  ~~~~~~~~~~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:174:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  174 |       operator<<(bool __n)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:174:23: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'bool'
  174 |       operator<<(bool __n)
      |                  ~~~~~^~~
In file included from /opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:833:
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/ostream.tcc:91:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char; _Traits = std::char_traits<char>]'
   91 |     basic_ostream<_CharT, _Traits>::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/ostream.tcc:92:22: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'short int'
   92 |     operator<<(short __n)
      |                ~~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:181:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  181 |       operator<<(unsigned short __n)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:181:33: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'short unsigned int'
  181 |       operator<<(unsigned short __n)
      |                  ~~~~~~~~~~~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/ostream.tcc:105:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char; _Traits = std::char_traits<char>]'
  105 |     basic_ostream<_CharT, _Traits>::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/ostream.tcc:106:20: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'int'
  106 |     operator<<(int __n)
      |                ~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:192:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  192 |       operator<<(unsigned int __n)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:192:31: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'unsigned int'
  192 |       operator<<(unsigned int __n)
      |                  ~~~~~~~~~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:201:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  201 |       operator<<(long long __n)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:201:28: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'long long int'
  201 |       operator<<(long long __n)
      |                  ~~~~~~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:205:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  205 |       operator<<(unsigned long long __n)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:205:37: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'long long unsigned int'
  205 |       operator<<(unsigned long long __n)
      |                  ~~~~~~~~~~~~~~~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:220:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  220 |       operator<<(double __f)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:220:25: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'double'
  220 |       operator<<(double __f)
      |                  ~~~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:224:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  224 |       operator<<(float __f)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:224:24: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'float'
  224 |       operator<<(float __f)
      |                  ~~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:232:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  232 |       operator<<(long double __f)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:232:30: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'long double'
  232 |       operator<<(long double __f)
      |                  ~~~~~~~~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:245:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  245 |       operator<<(const void* __p)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:245:30: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'const void*'
  245 |       operator<<(const void* __p)
      |                  ~~~~~~~~~~~~^~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:250:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::nullptr_t) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>; std::nullptr_t = std::nullptr_t]'
  250 |       operator<<(nullptr_t)
      |       ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:250:18: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'std::nullptr_t'
  250 |       operator<<(nullptr_t)
      |                  ^~~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/ostream.tcc:119:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(__streambuf_type*) [with _CharT = char; _Traits = std::char_traits<char>; __streambuf_type = std::basic_streambuf<char>]'
  119 |     basic_ostream<_CharT, _Traits>::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/ostream.tcc:120:34: note:   no known conversion for argument 1 from 'std::array<int, 1>' to 'std::basic_ostream<char>::__streambuf_type*' {aka 'std::basic_streambuf<char>*'}
  120 |     operator<<(__streambuf_type* __sbin)
      |                ~~~~~~~~~~~~~~~~~~^~~~~~
In file included from /opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/basic_string.h:48,
                 from /opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/string:53,
                 from /opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/locale_classes.h:40,
                 from /opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/ios_base.h:41,
                 from /opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ios:4,
                 from /opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:38:
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/string_view:672:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, basic_string_view<_CharT, _Traits>)'
  672 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/string_view:672:5: note:   template argument deduction/substitution failed:
delete.cpp:3:31: note:   'std::array<int, 1>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
    3 | main(){std::cout<<std::array{1};}
      |                               ^
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/basic_string.h:3883:5:note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3883 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/basic_string.h:3883:5:note:   template argument deduction/substitution failed:
delete.cpp:3:31: note:   'std::array<int, 1>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
    3 | main(){std::cout<<std::array{1};}
      |                               ^
In file included from /opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/ios_base.h:46:
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/system_error:279:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const error_code&)'
  279 |     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/system_error:279:5: note:   template argument deduction/substitution failed:
delete.cpp:3:24: note:   cannot convert 'std::array<int, 1>{std::__array_traits<int, 1>::_Type{1}}' (type 'std::array<int, 1>') to type 'const std::error_code&'
    3 | main(){std::cout<<std::array{1};}
      |                        ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:507:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _CharT)'
  507 |     operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:507:5: note:   template argument deduction/substitution failed:
delete.cpp:3:31: note:   deduced conflicting types for parameter '_CharT' ('cha' and 'std::array<int, 1>')
    3 | main(){std::cout<<std::array{1};}
      |                               ^
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:517:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, char)'
  517 |     operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:517:5: note:   template argument deduction/substitution failed:
delete.cpp:3:24: note:   cannot convert 'std::array<int, 1>{std::__array_traits<int, 1>::_Type{1}}' (type 'std::array<int, 1>') to type 'char'
    3 | main(){std::cout<<std::array{1};}
      |                        ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:523:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, char)'
  523 |     operator<<(basic_ostream<char, _Traits>& __out, char __c)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:523:5: note:   template argument deduction/substitution failed:
delete.cpp:3:24: note:   cannot convert 'std::array<int, 1>{std::__array_traits<int, 1>::_Type{1}}' (type 'std::array<int, 1>') to type 'char'
    3 | main(){std::cout<<std::array{1};}
      |                        ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:534:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, signed char)'
  534 |     operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:534:5: note:   template argument deduction/substitution failed:
delete.cpp:3:24: note:   cannot convert 'std::array<int, 1>{std::__array_traits<int, 1>::_Type{1}}' (type 'std::array<int, 1>') to type 'signed char'
    3 | main(){std::cout<<std::array{1};}
      |                        ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:539:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, unsigned char)'
  539 |     operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:539:5: note:   template argument deduction/substitution failed:
delete.cpp:3:24: note:   cannot convert 'std::array<int, 1>{std::__array_traits<int, 1>::_Type{1}}' (type 'std::array<int, 1>') to type 'unsigned char'
    3 | main(){std::cout<<std::array{1};}
      |                        ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:598:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const _CharT*)'
  598 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:598:5: note:   template argument deduction/substitution failed:
delete.cpp:3:31: note:   mismatched types 'const _CharT*' and 'std::array<int, 1>'
    3 | main(){std::cout<<std::array{1};}
      |                               ^
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/ostream.tcc:302:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const char*)'
  302 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/bits/ostream.tcc:302:5: note:   template argument deduction/substitution failed:
delete.cpp:3:24: note:   cannot convert 'std::array<int, 1>{std::__array_traits<int, 1>::_Type{1}}' (type 'std::array<int, 1>') to type 'const char*'
    3 | main(){std::cout<<std::array{1};}
      |                        ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:615:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const char*)'
  615 |     operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:615:5: note:   template argument deduction/substitution failed:
delete.cpp:3:24: note:   cannot convert 'std::array<int, 1>{std::__array_traits<int, 1>::_Type{1}}' (type 'std::array<int, 1>') to type 'const char*'
    3 | main(){std::cout<<std::array{1};}
      |                        ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:628:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const signed char*)'
  628 |     operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:628:5: note:   template argument deduction/substitution failed:
delete.cpp:3:24: note:   cannot convert 'std::array<int, 1>{std::__array_traits<int, 1>::_Type{1}}' (type 'std::array<int, 1>') to type 'const signed char*'
    3 | main(){std::cout<<std::array{1};}
      |                        ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:633:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const unsigned char*)'
  633 |     operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:633:5: note:   template argument deduction/substitution failed:
delete.cpp:3:24: note:   cannot convert 'std::array<int, 1>{std::__array_traits<int, 1>::_Type{1}}' (type 'std::array<int, 1>') to type 'const unsigned char*'
    3 | main(){std::cout<<std::array{1};}
      |                        ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:754:5: note: candidate: 'template<class _Ostream, class _Tp> _Ostream&& std::operator<<(_Ostream&&, const _Tp&)'
  754 |     operator<<(_Ostream&& __os, const _Tp& __x)
      |     ^~~~~~~~
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:754:5: note:   template argument deduction/substitution failed:
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream: In substitution of 'template<class _Ostream, class _Tp> _Ostream&& std::operator<<(_Ostream&&, const _Tp&) [with _Ostream = std::basic_ostream<char>&; _Tp = std::array<int, 1>]':
delete.cpp:3:31:   required from here
/opt/homebrew/Cellar/gcc@12/12.1.0_1/include/c++/12/ostream:754:5: error: no type named 'type' in 'struct std::enable_if<false, void>'

Another one, just to see what happens when you redefine important functions.
#define write std::array
#define memcpy printf
#include <iostream>

Compiled with Apple Clang 13.1.6 on macOS 12.4, with no options.
Error (18212 characters):
In file included from delete.cpp:4:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:37:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ios:214:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale:15:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/string:522:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/algorithm:652:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/cstring:60:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/string.h:60:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/string.h:72:7: error: functions that differ only in their return type cannot be overloaded
void    *memcpy(void *__dst, const void *__src, size_t __n);
~~~~~~~~~^
delete.cpp:3:16: note: expanded from macro 'memcpy'
#define memcpy cout
               ^
delete.cpp:2:14: note: expanded from macro 'cout'
#define cout printf
             ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/stdio.h:170:6: note: previous declaration is here
int      printf(const char * __restrict, ...) __printflike(1, 2);
~~~      ^
In file included from delete.cpp:4:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:37:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ios:214:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale:15:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/string:522:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/algorithm:653:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/functional:500:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/function.h:22:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/memory:799:23: error: cannot initialize a parameter of type 'const char *' with an rvalue of type 'void *'
        _VSTD::memcpy(static_cast<void*>(__end2), static_cast<void const*>(__begin1), _Np * sizeof(_Tp));
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/stdio.h:170:36: note: passing argument to parameter here
int      printf(const char * __restrict, ...) __printflike(1, 2);
                                       ^
In file included from delete.cpp:4:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:38:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/istream:163:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:221:20: error: non-friend class member 'array' cannot have a qualified name
    basic_ostream& write(const char_type* __s, streamsize __n);
                   ^~~~~
delete.cpp:1:20: note: expanded from macro 'write'
#define write std::array
              ~~~~~^
In file included from delete.cpp:4:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:38:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/istream:163:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:905:45: error: unknown type name 'char_type'
basic_ostream<_CharT, _Traits>::write(const char_type* __s, streamsize __n)
                                            ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:905:33: error: nested name specifier 'basic_ostream<_CharT, _Traits>::std::' for declaration does not refer into a class, class template or class template partial specialization
basic_ostream<_CharT, _Traits>::write(const char_type* __s, streamsize __n)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
delete.cpp:1:20: note: expanded from macro 'write'
#define write std::array
                   ^
In file included from delete.cpp:4:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:38:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/istream:163:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:911:9: error: unknown type name 'sentry'
        sentry __sen(*this);
        ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:911:23: error: invalid use of 'this' outside of a non-static member function
        sentry __sen(*this);
                      ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:912:22: error: use of undeclared identifier '__n'
        if (__sen && __n)
                     ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:914:17: error: invalid use of 'this' outside of a non-static member function
            if (this->rdbuf()->sputn(__s, __n) != __n)
                ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:914:38: error: use of undeclared identifier '__s'
            if (this->rdbuf()->sputn(__s, __n) != __n)
                                     ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:914:43: error: use of undeclared identifier '__n'
            if (this->rdbuf()->sputn(__s, __n) != __n)
                                          ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:914:51: error: use of undeclared identifier '__n'
            if (this->rdbuf()->sputn(__s, __n) != __n)
                                                  ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:915:17: error: invalid use of 'this' outside of a non-static member function
                this->setstate(ios_base::badbit);
                ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:921:9: error: invalid use of 'this' outside of a non-static member function
        this->__set_badbit_and_consider_rethrow();
        ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ostream:924:13: error: invalid use of 'this' outside of a non-static member function
    return *this;
            ^
In file included from delete.cpp:4:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:55:33: error: declaration conflicts with target of using declaration already in scope
extern _LIBCPP_FUNC_VIS ostream cout;
                                ^
delete.cpp:2:14: note: expanded from macro 'cout'
#define cout printf
             ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/stdio.h:170:6: note: target of using declaration
int      printf(const char * __restrict, ...) __printflike(1, 2);
         ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/cstdio:169:9: note: using declaration
using ::printf _LIBCPP_USING_IF_EXISTS;
        ^
In file included from delete.cpp:4:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:37:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ios:214:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale:15:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/string:522:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/algorithm:653:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/functional:500:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/function.h:20:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/shared_ptr.h:25:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/unique_ptr.h:15:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:40:19: error: cannot initialize a parameter of type 'const char *' with an rvalue of type 'unsigned int *'
    _VSTD::memcpy(&__r, __p, sizeof(__r));
                  ^~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:138:28: note: in instantiation of function template specialization 'std::__loadword<unsigned int>' requested here
      const uint32_t __a = __loadword<uint32_t>(__s);
                           ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:229:14: note: in instantiation of member function 'std::__murmur2_or_cityhash<unsigned long, 64>::__hash_len_0_to_16' requested here
      return __hash_len_0_to_16(__s, __len);
             ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:347:16: note: in instantiation of member function 'std::__murmur2_or_cityhash<unsigned long, 64>::operator()' requested here
        return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
               ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:421:20: note: in instantiation of member function 'std::__scalar_hash<std::_PairT, 2>::operator()' requested here
    return _HashT()(__p);
                   ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/stdio.h:170:36: note: passing argument to parameter here
int      printf(const char * __restrict, ...) __printflike(1, 2);
                                       ^
In file included from delete.cpp:4:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:37:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ios:214:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale:15:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/string:522:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/algorithm:653:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/functional:500:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/function.h:20:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/shared_ptr.h:25:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/unique_ptr.h:15:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:40:19: error: cannot initialize a parameter of type 'const char *' with an rvalue of type 'unsigned long *'
    _VSTD::memcpy(&__r, __p, sizeof(__r));
                  ^~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:239:15: note: in instantiation of function template specialization 'std::__loadword<unsigned long>' requested here
  _Size __x = __loadword<_Size>(__s + __len - 40);
              ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:347:16: note: in instantiation of member function 'std::__murmur2_or_cityhash<unsigned long, 64>::operator()' requested here
        return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
               ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:421:20: note: in instantiation of member function 'std::__scalar_hash<std::_PairT, 2>::operator()' requested here
    return _HashT()(__p);
                   ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/stdio.h:170:36: note: passing argument to parameter here
int      printf(const char * __restrict, ...) __printflike(1, 2);
                                       ^
In file included from delete.cpp:4:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:37:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ios:214:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale:15:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/string:522:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/algorithm:653:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/functional:500:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/function.h:20:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/shared_ptr.h:25:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/unique_ptr.h:15:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:185:42: error: no matching function for call to '__loadword'
    return __weak_hash_len_32_with_seeds(__loadword<_Size>(__s),
                                         ^~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:244:28: note: in instantiation of member function 'std::__murmur2_or_cityhash<unsigned long, 64>::__weak_hash_len_32_with_seeds' requested here
  pair<_Size, _Size> __v = __weak_hash_len_32_with_seeds(__s + __len - 64, __len, __z);
                           ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:347:16: note: in instantiation of member function 'std::__murmur2_or_cityhash<unsigned long, 64>::operator()' requested here
        return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
               ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:421:20: note: in instantiation of member function 'std::__scalar_hash<std::_PairT, 2>::operator()' requested here
    return _HashT()(__p);
                   ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__functional/hash.h:37:1: note: candidate template ignored: substitution failure [with _Size = unsigned long]
__loadword(const void* __p)
^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.

Welcome to Code Golf, and nice first answer! Does expanding the array make the error substantially larger?

50 bytes: Result will be the sum of the length of all the positive numbers with a single error message:

#include<utility>
std::make_index_sequence<-1>::x;

174 bytes: quadratic explosion with multiple error messages:

#include<utility>
template<size_t N, size_t... M>
void a(std::index_sequence<N, M...>) {
  a(std::index_sequence<M...>{});
  static_assert(!N);
}
auto x{a(std::make_index_sequence<C>{})};

compile with
g++ -c truc.cpp -std=c++17 -DC=10 2>&1 > /dev/null | wc -c

index_sequence seems to bypass the template instantiation depth limit problem

for C=10:    8238 chars
for C=100:   264288 chars
for C=1000:  23118522 chars

errors look like this: the whole 0 ... C-1 number sequence looks like it is printed 4*C times
truc.cpp:7:6: error: « void x » a un type incomplet
 auto x{a(std::make_index_sequence<C>{})};
      ^
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] » :
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
   static_assert(!N);
   ^~~~~~~~~~~~~
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 2; long unsigned int ...M = {3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 3; long unsigned int ...M = {4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 4; long unsigned int ...M = {5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 5; long unsigned int ...M = {6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>  » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 6; long unsigned int ...M = {7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 6, 7, 8, 9, 10, 11, 12, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 7; long unsigned int ...M = {8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 7, 8, 9, 10, 11, 12, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 8; long unsigned int ...M = {9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 8, 9, 10, 11, 12, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 9; long unsigned int ...M = {10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 9, 10, 11, 12, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 10; long unsigned int ...M = {11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 10, 11, 12, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 11; long unsigned int ...M = {12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 11, 12, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 12; long unsigned int ...M = {13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 12, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 13; long unsigned int ...M = {14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 13, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:5:3: error: l'assertion statique a échoué
truc.cpp: Dans l'instanciation de « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 14; long unsigned int ...M = {}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 14>] » :
truc.cpp:4:4:   requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:4:4:   requis par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 0; long unsigned int ...M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14>] »
truc.cpp:7:39:   requis depuis ici
truc.cpp:4:4: error: pas de fonction correspondant à l'appel « a(std::index_sequence<>) »
   a(std::index_sequence<M...>{});
   ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
truc.cpp:3:6: note: candidate: template<long unsigned int N, long unsigned int ...M> void a(std::index_sequence<N, M ...>)
 void a(std::index_sequence<N, M...>) {
      ^
truc.cpp:3:6: note:   la déduction/substitution de l'argument du patron a échoué:
truc.cpp:4:4: note:   le candidat attend 2 arguments, 0 fourni(s)
   a(std::index_sequence<M...>{});
   ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
truc.cpp:5:3: error: l'assertion statique a échoué
   static_assert(!N);
   ^~~~~~~~~~~~~
[1]    11052 exit 1     g++ -c -O3 truc.cpp -std=c++17 -DC=15

and the number sequences are able to go past the default template instantiation depth limit, certainly because it's a builtin:
... requis récursivement par « void a(std::index_sequence<N, M ...>) [avec long unsigned int N = 1; long unsigned int ...M = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 269, 270, 271, 272, 273, 274, 275, 276, 277, 278, 279, 280, 281, 282, 283, 284, 285, 286, 287, 288, 289, 290, 291, 292, 293, 294, 295, 296, 297, 298, 299, 300, 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312, 313, 314, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, 325, 326, 327, 328, 329, 330, 331, 332, 333, 334, 335, 336, 337, 338, 339, 340, 341, 342, 343, 344, 345, 346, 347, 348, 349, 350, 351, 352, 353, 354, 355, 356, 357, 358, 359, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 420, 421, 422, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 460, 461, 462, 463, 464, 465, 466, 467, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 478, 479, 480, 481, 482, 483, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 496, 497, 498, 499, 500, 501, 502, 503, 504, 505, 506, 507, 508, 509, 510, 511, 512, 513, 514, 515, 516, 517, 518, 519, 520, 521, 522, 523, 524, 525, 526, 527, 528, 529, 530, 531, 532, 533, 534, 535, 536, 537, 538, 539, 540, 541, 542, 543, 544, 545, 546, 547, 548, 549, 550, 551, 552, 553, 554, 555, 556, 557, 558, 559, 560, 561, 562, 563, 564, 565, 566, 567, 568, 569, 570, 571, 572, 573, 574, 575, 576, 577, 578, 579, 580, 581, 582, 583, 584, 585, 586, 587, 588, 589, 590, 591, 592, 593, 594, 595, 596, 597, 598, 599, 600, 601, 602, 603, 604, 605, 606, 607, 608, 609, 610, 611, 612, 613, 614, 615, 616, 617, 618, 619, 620, 621, 622, 623, 624, 625, 626, 627, 628, 629, 630, 631, 632, 633, 634, 635, 636, 637, 638, 639, 640, 641, 642, 643, 644, 645, 646, 647, 648, 649, 650, 651, 652, 653, 654, 655, 656, 657, 658, 659, 660, 661, 662, 663, 664, 665, 666, 667, 668, 669, 670, 671, 672, 673, 674, 675, 676, 677, 678, 679, 680, 681, 682, 683, 684, 685, 686, 687, 688, 689, 690, 691, 692, 693, 694, 695, 696, 697, 698, 699, 700, 701, 702, 703, 704, 705, 706, 707, 708, 709, 710, 711, 712, 713, 714, 715, 716, 717, 718, 719, 720, 721, 722, 723, 724, 725, 726, 727, 728, 729, 730, 731, 732, 733, 734, 735, 736, 737, 738, 739, 740, 741, 742, 743, 744, 745, 746, 747, 748, 749, 750, 751, 752, 753, 754, 755, 756, 757, 758, 759, 760, 761, 762, 763, 764, 765, 766, 767, 768, 769, 770, 771, 772, 773, 774, 775, 776, 777, 778, 779, 780, 781, 782, 783, 784, 785, 786, 787, 788, 789, 790, 791, 792, 793, 794, 795, 796, 797, 798, 799, 800, 801, 802, 803, 804, 805, 806, 807, 808, 809, 810, 811, 812, 813, 814, 815, 816, 817, 818, 819, 820, 821, 822, 823, 824, 825, 826, 827, 828, 829, 830, 831, 832, 833, 834, 835, 836, 837, 838, 839, 840, 841, 842, 843, 844, 845, 846, 847, 848, 849, 850, 851, 852, 853, 854, 855, 856, 857, 858, 859, 860, 861, 862, 863, 864, 865, 866, 867, 868, 869, 870, 871, 872, 873, 874, 875, 876, 877, 878, 879, 880, 881, 882, 883, 884, 885, 886, 887, 888, 889, 890, 891, 892, 893, 894, 895, 896, 897, 898, 899, 900, 901, 902, 903, 904, 905, 906, 907, 908, 909, 910, 911, 912, 913, 914, 915, 916, 917, 918, 919, 920, 921, 922, 923, 924, 925, 926, 927, 928, 929, 930, 931, 932, 933, 934, 935, 936, 937, 938, 939, 940, 941, 942, 943, 944, 945, 946, 947, 948, 949, 950, 951, 952, 953, 954, 955, 956, 957, 958, 959, 960, 961, 962, 963, 964, 965, 966, 967, 968, 969, 970, 971, 972, 973, 974, 975, 976, 977, 978, 979, 980, 981, 982, 983, 984, 985, 986, 987, 988, 989, 990, 991, 992, 993, 994, 995, 996, 997, 998, 999, 1000, 1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008, 1009, 1010, 1011, 1012, 1013, 1014, 1015, 1016, 1017, 1018, 1019, 1020, 1021, 1022, 1023, 1024, 1025, 1026, 1027, 1028, 1029, 1030, 1031, 1032, 1033, 1034, 1035, 1036, 1037, 1038, 1039, 1040, 1041, 1042, 1043, 1044, 1045, 1046, 1047, 1048, 1049, 1050, 1051, 1052, 1053, 1054, 1055, 1056, 1057, 1058, 1059, 1060, 1061, 1062, 1063, 1064, 1065, 1066, 1067, 1068, 1069, 1070, 1071, 1072, 1073, 1074, 1075, 1076, 1077, 1078, 1079, 1080, 1081, 1082, 1083, 1084, 1085, 1086, 1087, 1088, 1089, 1090, 1091, 1092, 1093, 1094, 1095, 1096, 1097, 1098, 1099, 1100, 1101, 1102, 1103, 1104, 1105, 1106, 1107, 1108, 1109, 1110, 1111, 1112, 1113, 1114, 1115, 1116, 1117, 1118, 1119, 1120, 1121, 1122, 1123, 1124, 1125, 1126, 1127, 1128, 1129, 1130, 1131, 1132, 1133, 1134, 1135, 1136, 1137, 1138, 1139, 1140, 1141, 1142, 1143, 1144, 1145, 1146, 1147, 1148, 1149, 1150, 1151, 1152, 1153, 1154, 1155, 1156, 1157, 1158, 1159, 1160, 1161, 1162, 1163, 1164, 1165, 1166, 1167, 1168, 1169, 1170, 1171, 1172, 1173, 1174, 1175, 1176, 1177, 1178, 1179, 1180, 1181, 1182, 1183, 1184, 1185, 1186, 1187, 1188, 1189, 1190, 1191, 1192, 1193, 1194, 1195, 1196, 1197, 1198, 1199, 1200, 1201, 1202, 1203, 1204, 1205, 1206, 1207, 1208, 1209, 1210, 1211, 1212, 1213, 1214, 1215, 1216, 1217, 1218, 1219, 1220, 1221, 1222, 1223, 1224, 1225, 1226, 1227, 1228, 1229, 1230, 1231, 1232, 1233, 1234, 1235, 1236, 1237, 1238, 1239, 1240, 1241, 1242, 1243, 1244, 1245, 1246, 1247, 1248, 1249, 1250, 1251, 1252, 1253, 1254, 1255, 1256, 1257, 1258, 1259, 1260, 1261, 1262, 1263, 1264, 1265, 1266, 1267, 1268, 1269, 1270, 1271, 1272, 1273, 1274, 1275, 1276, 1277, 1278, 1279, 1280, 1281, 1282, 1283, 1284, 1285, 1286, 1287, 1288, 1289, 1290, 1291, 1292, 1293, 1294, 1295, 1296, 1297, 1298, 1299, 1300, 1301, 1302, 1303, 1304, 1305, 1306, 1307, 1308, 1309, 1310, 1311, 1312, 1313, 1314, 1315, 1316, 1317, 1318, 1319, 1320, 1321, 1322, 1323, 1324, 1325, 1326, 1327, 1328, 1329, 1330, 1331, 1332, 1333, 1334, 1335, 1336, 1337, 1338, 1339, 1340, 1341, 1342, 1343, 1344, 1345, 1346, 1347, 1348, 1349, 1350, 1351, 1352, 1353, 1354, 1355, 1356, 1357, 1358, 1359, 1360, 1361, 1362, 1363, 1364, 1365, 1366, 1367, 1368, 1369, 1370, 1371, 1372, 1373, 1374, 1375, 1376, 1377, 1378, 1379, 1380, 1381, 1382, 1383, 1384, 1385, 1386, 1387, 1388, 1389, 1390, 1391, 1392, 1393, 1394, 1395, 1396, 1397, 1398, 1399, 1400, 1401, 1402, 1403, 1404, 1405, 1406, 1407, 1408, 1409, 1410, 1411, 1412, 1413, 1414, 1415, 1416, 1417, 1418, 1419, 1420, 1421, 1422, 1423, 1424, 1425, 1426, 1427, 1428, 1429, 1430, 1431, 1432, 1433, 1434, 1435, 1436, 1437, 1438, 1439, 1440, 1441, 1442, 1443, 1444, 1445, 1446, 1447, 1448, 1449, 1450, 1451, 1452, 1453, 1454, 1455, 1456, 1457, 1458, 1459, 1460, 1461, 1462, 1463, 1464, 1465, 1466, 1467, 1468, 1469, 1470, 1471, 1472, 1473, 1474, 1475, 1476, 1477, 1478, 1479, 1480, 1481, 1482, 1483, 1484, 1485, 1486, 1487, 1488, 1489, 1490, 1491, 1492, 1493, 1494, 1495, 1496, 1497, 1498, 1499}; std::index_sequence<N, M ...> = std::integer_sequence<long unsigned int, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 269, 270, 271, 272, 273, 274, 275, 276, 277, 278, 279, 280, 281, 282, 283, 284, 285, 286, 287, 288, 289, 290, 291, 292, 293, 294, 295, 296, 297, 298, 299, 300, 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312, 313, 314, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, 325, 326, 327, 328, 329, 330, 331, 332, 333, 334, 335, 336, 337, 338, 339, 340, 341, 342, 343, 344, 345, 346, 347, 348, 349, 350, 351, 352, 353, 354, 355, 356, 357, 358, 359, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 420, 421, 422, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 460, 461, 462, 463, 464, 465, 466, 467, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 478, 479, 480, 481, 482, 483, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 496, 497, 498, 499, 500, 501, 502, 503, 504, 505, 506, 507, 508, 509, 510, 511, 512, 513, 514, 515, 516, 517, 518, 519, 520, 521, 522, 523, 524, 525, 526, 527, 528, 529, 530, 531, 532, 533, 534, 535, 536, 537, 538, 539, 540, 541, 542, 543, 544, 545, 546, 547, 548, 549, 550, 551, 552, 553, 554, 555, 556, 557, 558, 559, 560, 561, 562, 563, 564, 565, 566, 567, 568, 569, 570, 571, 572, 573, 574, 575, 576, 577, 578, 579, 580, 581, 582, 583, 584, 585, 586, 587, 588, 589, 590, 591, 592, 593, 594, 595, 596, 597, 598, 599, 600, 601, 602, 603, 604, 605, 606, 607, 608, 609, 610, 611, 612, 613, 614, 615, 616, 617, 618, 619, 620, 621, 622, 623, 624, 625, 626, 627, 628, 629, 630, 631, 632, 633, 634, 635, 636, 637, 638, 639, 640, 641, 642, 643, 644, 645, 646, 647, 648, 649, 650, 651, 652, 653, 654, 655, 656, 657, 658, 659, 660, 661, 662, 663, 664, 665, 666, 667, 668, 669, 670, 671, 672, 673, 674, 675, 676, 677, 678, 679, 680, 681, 682, 683, 684, 685, 686, 687, 688, 689, 690, 691, 692, 693, 694, 695, 696, 697, 698, 699, 700, 701, 702, 703, 704, 705, 706, 707, 708, 709, 710, 711, 712, 713, 714, 715, 716, 717, 718, 719, 720, 721, 722, 723, 724, 725, 726, 727, 728, 729, 730, 731, 732, 733, 734, 735, 736, 737, 738, 739, 740, 741, 742, 743, 744, 745, 746, 747, 748, 749, 750, 751, 752, 753, 754, 755, 756, 757, 758, 759, 760, 761, 762, 763, 764, 765, 766, 767, 768, 769, 770, 771, 772, 773, 774, 775, 776, 777, 778, 779, 780, 781, 782, 783, 784, 785, 786, 787, 788, 789, 790, 791, 792, 793, 794, 795, 796, 797, 798, 799, 800, 801, 802, 803, 804, 805, 806, 807, 808, 809, 810, 811, 812, 813, 814, 815, 816, 817, 818, 819, 820, 821, 822, 823, 824, 825, 826, 827, 828, 829, 830, 831, 832, 833, 834, 835, 836, 837, 838, 839, 840, 841, 842, 843, 844, 845, 846, 847, 848, 849, 850, 851, 852, 853, 854, 855, 856, 857, 858, 859, 860, 861, 862, 863, 864, 865, 866, 867, 868, 869, 870, 871, 872, 873, 874, 875, 876, 877, 878, 879, 880, 881, 882, 883, 884, 885, 886, 887, 888, 889, 890, 891, 892, 893, 894, 895, 896, 897, 898, 899, 900, 901, 902, 903, 904, 905, 906, 907, 908, 909, 910, 911, 912, 913, 914, 915, 916, 917, 918, 919, 920, 921, 922, 923, 924, 925, 926, 927, 928, 929, 930, 931, 932, 933, 934, 935, 936, 937, 938, 939, 940, 941, 942, 943, 944, 945, 946, 947, 948, 949, 950, 951, 952, 953, 954, 955, 956, 957, 958, 959, 960, 961, 962, 963, 964, 965, 966, 967, 968, 969, 970, 971, 972, 973, 974, 975, 976, 977, 978, 979, 980, 981, 982, 983, 984, 985, 986, 987, 988, 989, 990, 991, 992, 993, 994, 995, 996, 997, 998, 999, 1000, 1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008, 1009, 1010, 1011, 1012, 1013, 1014, 1015, 1016, 1017, 1018, 1019, 1020, 1021, 1022, 1023, 1024, 1025, 1026, 1027, 1028, 1029, 1030, 1031, 1032, 1033, 1034, 1035, 1036, 1037, 1038, 1039, 1040, 1041, 1042, 1043, 1044, 1045, 1046, 1047, 1048, 1049, 1050, 1051, 1052, 1053, 1054, 1055, 1056, 1057, 1058, 1059, 1060, 1061, 1062, 1063, 1064, 1065, 1066, 1067, 1068, 1069, 1070, 1071, 1072, 1073, 1074, 1075, 1076, 1077, 1078, 1079, 1080, 1081, 1082, 1083, 1084, 1085, 1086, 1087, 1088, 1089, 1090, 1091, 1092, 1093, 1094, 1095, 1096, 1097, 1098, 1099, 1100, 1101, 1102, 1103, 1104, 1105, 1106, 1107, 1108, 1109, 1110, 1111, 1112, 1113, 1114, 1115, 1116, 1117, 1118, 1119, 1120, 1121, 1122, 1123, 1124, 1125, 1126, 1127, 1128, 1129, 1130, 1131, 1132, 1133, 1134, 1135, 1136, 1137, 1138, 1139, 1140, 1141, 1142, 1143, 1144, 1145, 1146, 1147, 1148, 1149, 1150, 1151, 1152, 1153, 1154, 1155, 1156, 1157, 1158, 1159, 1160, 1161, 1162, 1163, 1164, 1165, 1166, 1167, 1168, 1169, 1170, 1171, 1172, 1173, 1174, 1175, 1176, 1177, 1178, 1179, 1180, 1181, 1182, 1183, 1184, 1185, 1186, 1187, 1188, 1189, 1190, 1191, 1192, 1193, 1194, 1195, 1196, 1197, 1198, 1199, 1200, 1201, 1202, 1203, 1204, 1205, 1206, 1207, 1208, 1209, 1210, 1211, 1212, 1213, 1214, 1215, 1216, 1217, 1218, 1219, 1220, 1221, 1222, 1223, 1224, 1225, 1226, 1227, 1228, 1229, 1230, 1231, 1232, 1233, 1234, 1235, 1236, 1237, 1238, 1239, 1240, 1241, 1242, 1243, 1244, 1245, 1246, 1247, 1248, 1249, 1250, 1251, 1252, 1253, 1254, 1255, 1256, 1257, 1258, 1259, 1260, 1261, 1262, 1263, 1264, 1265, 1266, 1267, 1268, 1269, 1270, 1271, 1272, 1273, 1274, 1275, 1276, 1277, 1278, 1279, 1280, 1281, 1282, 1283, 1284, 1285, 1286, 1287, 1288, 1289, 1290, 1291, 1292, 1293, 1294, 1295, 1296, 1297, 1298, 1299, 1300, 1301, 1302, 1303, 1304, 1305, 1306, 1307, 1308, 1309, 1310, 1311, 1312, 1313, 1314, 1315, 1316, 1317, 1318, 1319, 1320, 1321, 1322, 1323, 1324, 1325, 1326, 1327, 1328, 1329, 1330, 1331, 1332, 1333, 1334, 1335, 1336, 1337, 1338, 1339, 1340, 1341, 1342, 1343, 1344, 1345, 1346, 1347, 1348, 1349, 1350, 1351, 1352, 1353, 1354, 1355, 1356, 1357, 1358, 1359, 1360, 1361, 1362, 1363, 1364, 1365, 1366, 1367, 1368, 1369, 1370, 1371, 1372, 1373, 1374, 1375, 1376, 1377, 1378, 1379, 1380, 1381, 1382, 1383, 1384, 1385, 1386, 1387, 1388, 1389, 1390, 1391, 1392, 1393, 1394, 1395, 1396, 1397, 1398, 1399, 1400, 1401, 1402, 1403, 1404, 1405, 1406, 1407, 1408, 1409, 1410, 1411, 1412, 1413, 1414, 1415, 1416, 1417, 1418, 1419, 1420, 1421, 1422, 1423, 1424, 1425, 1426, 1427, 1428, 1429, 1430, 1431, 1432, 1433, 1434, 1435, 1436, 1437, 1438, 1439, 1440, 1441, 1442, 1443, 1444, 1445, 1446, 1447, 1448, 1449, 1450, 1451, 1452, 1453, 1454, 1455, 1456, 1457, 1458, 1459, 1460, 1461, 1462, 1463, 1464, 1465, 1466, 1467, 1468, 1469, 1470, 1471, 1472, 1473, 1474, 1475, 1476, 1477, 1478, 1479, 1480, 1481, 1482, 1483, 1484, 1485, 1486, 1487, 1488, 1489, 1490, 1491, 1492, 1493, 1494, 1495, 1496, 1497, 1498, 1499>

with -std=c++20 flag:
a<b<c<d<e<f<g

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