Structs

Enums

Used to forbid let expressions in certain syntactic locations.
Is self allowed semantically as the first parameter in an FnDecl?

Constants

Functions

When encountering an equality constraint in a where clause, emit an error. If the code seems like it’s setting an associated type, provide an appropriate suggestion.
Checks that generic parameters are in the correct order, which is lifetimes, then types and then consts. (<'a, T, const N: usize>)