d92a1bd7cc
Allow higher-ranked fn sigs in `ValuePairs` For better bookkeeping -- only affects diagnostic path. Allow reporting signature mismatches like "signature"s and not "fn pointer"s. Improves https://github.com/rust-lang/rust/pull/115897#discussion_r1331940846
For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc dev guide.