(..=0 | 2) in macro does not compile without parentheses but generates warning for unnecessary parentheses

[astra90x]

I tried this code:

matches!(2, ..=0 | 2)

matches!(2, (..=0 | 2))

I expected to see this happen: At least one of the expressions should compile without warning.

Instead, this happened: The first expression does not compile. The second expression generates a warning asking you to remove the parentheses.

This happens with any macro with a pattern matcher that ends up used. Skipping the parentheses does compile if the unstable exclusive range patterns are used, so I imagine this should work as well.

   Compiling playground v0.0.1 (/playground)
error: no rules expected the token `..=`
   --> src/lib.rs:2:17
    |
2   |     matches!(2, ..=0 | 2);
    |                 ^^^ no rules expected this token in macro call
    |
note: while trying to match meta-variable `$pattern:pat`
   --> /playground/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/macros/mod.rs:430:24
    |
430 |     ($expression:expr, $pattern:pat $(if $guard:expr)? $(,)?) => {
    |                        ^^^^^^^^^^^^

warning: unnecessary parentheses around pattern
 --> src/lib.rs:3:17
  |
3 |     matches!(2, (..=0 | 2));
  |                 ^        ^
  |
  = note: `#[warn(unused_parens)]` on by default
help: remove these parentheses
  |
3 -     matches!(2, (..=0 | 2));
3 +     matches!(2, ..=0 | 2);
  |

warning: `playground` (lib) generated 1 warning
error: could not compile `playground` (lib) due to previous error; 1 warning emitted

Meta

rustc --version --verbose:

rustc 1.75.0 (82e1608df 2023-12-21)
binary: rustc
commit-hash: 82e1608dfa6e0b5569232559e3d385fea5a93112
commit-date: 2023-12-21
host: x86_64-unknown-linux-gnu
release: 1.75.0
LLVM version: 17.0.6

[astra90x]

I found the relevant missing DotDotEq here, and permitting ..= there would be the easiest thing to do. That is technically a breaking change though, so I'm not sure if we'd like to limit it to edition 2024 instead. In that case, we may also want to remove the warning for the current edition, which is an issue or patterns also have.

[Jules-Bertholet]

@rustbot label A-macros A-patterns A-lint A-suggestion-diagnostics D-invalid-suggestion T-compiler