syntax_data: {"ast_node_type":"variable","tokens":[{"end":92,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let (typing_env, mut self_ty, mut impl_trait_ref) = if generics.count() > args.len()
context_before:         // instances, like `impl<A> Tr<A> for ()` where `A` is substituted w/ `(T,)`.
context_after:             || &args[..generics.count()]