issue-link js-issue-link" data-error-text="Failed to load title" data-id="687493937" data-permission-text="Title is private" data-url="/~https://github.com/rust-lang/rust/issues/76001" data-hovercard-type="issue" data-hovercard-url="/rust-lang/rust/issues/76001/hovercard" href="/~https://github.com/rust-lang/rust/issues/76001">rust-lang#76001) and `let_chains` (rust-lang#53667) inside macros' `expr` patterns in a future edition by bifurcating the `expr` nonterminal in a similar way to `pat2021` to remove some backwards compatibility exceptions that disallow `const`/`let` at the beginning of an `expr` match. Fixes rust-lang#84155 and relaxes the backward compat restriction from rust-lang#80135 for a future edition. This is not intended to go into 2021 as it I don't think it's simple to write an automatic fix, and certainly not now that it's past the soft deadline for inclusion in 2021 by a long shot. Here is a pathological case of rust-lang#79908 that forces this to be an edition change: ```rust macro_rules! evil { ($e:expr) => { // or something else const {$e-1} }; (const $b:block) => { const {$b} } } fn main() { let x = 5; match x { evil!(const { 5 }) => panic!("oh no"), _ => (), }; } ```

Commits

Commits on Apr 26, 2021

Add expr202x macro pattern

Add `expr202x` macro pattern