76e755cf4a
Use if-let guards in the codebase and various other pattern cleanups Dogfooding if-let guards as experimentation for the feature. Tracking issue #51114. Conflicts with #87937.
The rustc_ast crate contains those things concerned purely with syntax
– that is, the AST ("abstract syntax tree"), parser, pretty-printer,
lexer, macro expander, and utilities for traversing ASTs.
For more information about how these things work in rustc, see the rustc dev guide: