Rollup merge of #118868 - Nadrieril:correctly-gate-never_patterns-parsing, r=petrochenkov

Correctly gate the parsing of match arms without body

https://github.com/rust-lang/rust/pull/118527 accidentally allowed the following to parse on stable:
```rust
match Some(0) {
    None => { foo(); }
    #[cfg(FALSE)]
    Some(_)
}
```

This fixes that oversight. The way I choose which error to emit is the best I could think of, I'm open if you know a better way.

r? `@petrochenkov` since you're the one who noticed

1 files changed, 9 insertions, 1 deletions

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 3c0627526be..5b0011e9f70 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -2918,7 +2918,15 @@ impl<'a> Parser<'a> {
             let mut result = if !is_fat_arrow && !is_almost_fat_arrow {
                 // A pattern without a body, allowed for never patterns.
                 arm_body = None;
-                this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
+                this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)]).map(
+                    |x| {
+                        // Don't gate twice
+                        if !pat.contains_never_pattern() {
+                            this.sess.gated_spans.gate(sym::never_patterns, pat.span);
+                        }
+                        x
+                    },
+                )
             } else {
                 if let Err(mut err) = this.expect(&token::FatArrow) {
                     // We might have a `=>` -> `=` or `->` typo (issue #89396).