Rollup merge of #121917 - GuillaumeGomez:pattern-complexity_limit.rs, r=Nadrieril

Add new `pattern_complexity` attribute to add possibility to limit and check recursion in pattern matching

Needed for https://github.com/rust-lang/rust-analyzer/issues/9528.

This PR adds a new attribute only available when running rust testsuite called `pattern_complexity` which allows to set the maximum recursion for the pattern matching. It is quite useful to ensure the complexity doesn't grow, like in `tests/ui/pattern/usefulness/issue-118437-exponential-time-on-diagonal-match.rs`.

r? `@Nadrieril`

1 files changed, 5 insertions, 0 deletions

diff --git a/compiler/rustc_pattern_analysis/src/rustc.rs b/compiler/rustc_pattern_analysis/src/rustc.rs
index f8839b0b590..5f5bfa7154a 100644
--- a/compiler/rustc_pattern_analysis/src/rustc.rs
+++ b/compiler/rustc_pattern_analysis/src/rustc.rs
@@ -895,6 +895,11 @@ impl<'p, 'tcx: 'p> TypeCx for RustcMatchCheckCtxt<'p, 'tcx> {
             errors::OverlappingRangeEndpoints { overlap: overlaps, range: pat_span },
         );
     }
+
+    fn complexity_exceeded(&self) -> Result<(), Self::Error> {
+        let span = self.whole_match_span.unwrap_or(self.scrut_span);
+        Err(self.tcx.dcx().span_err(span, "reached pattern complexity limit"))
+    }
 }
 
 /// Recursively expand this pattern into its subpatterns. Only useful for or-patterns.