syntax_data: {"ast_node_type":"other","tokens":[{"end":85,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // instances, like `impl<A> Tr<A> for ()` where `A` is substituted w/ `(T,)`.
context_before:         // NOTE: We don't support mangling partially substituted but still polymorphic
context_after:         let (typing_env, mut self_ty, mut impl_trait_ref) = if generics.count() > args.len()