e9d2227328
Add meta-variable checks in macro definitions This is an implementation of #61053. It is not sound (some errors are not reported) and not complete (reports may not be actual errors). This is due to the possibility to define macros in macros in indirect ways. See module documentation of `macro_check` for more details. What remains to be done: - [x] Migrate from an error to an allow-by-default lint. - [x] Add more comments in particular for the handling of nested macros. - [x] Add more tests if needed. - [x] Try to avoid cloning too much (one idea is to use lists on the stack). - [ ] Run crater with deny-by-default lint (measure rate of false positives). - [ ] Remove extra commit for deny-by-default lint - [x] Create a PR to remove the old `question_mark_macro_sep` lint #62160
The syntax 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 guide: