44e3daf5ee
Implement edition-based macro :pat feature This PR does two things: 1. Fixes the perf regression from https://github.com/rust-lang/rust/pull/80100#issuecomment-750893149 2. Implements `:pat2018` and `:pat2021` matchers, as described by `@joshtriplett` in https://github.com/rust-lang/rust/issues/54883#issuecomment-745509090 behind the feature gate `edition_macro_pat`. r? `@petrochenkov` cc `@Mark-Simulacrum`
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: