0cd939e36c
Implement a lint to warn about unused macro rules This implements a new lint to warn about unused macro rules (arms/matchers), similar to the `unused_macros` lint added by #41907 that warns about entire macros. ```rust macro_rules! unused_empty { (hello) => { println!("Hello, world!") }; () => { println!("empty") }; //~ ERROR: 1st rule of macro `unused_empty` is never used } fn main() { unused_empty!(hello); } ``` Builds upon #96149 and #96156. Fixes #73576
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