1 files changed, 8 insertions, 1 deletions

diff --git a/crates/hir_ty/src/diagnostics/match_check/usefulness.rs b/crates/hir_ty/src/diagnostics/match_check/usefulness.rs
index 44e08b6e9..cb322a3de 100644
--- a/crates/hir_ty/src/diagnostics/match_check/usefulness.rs
+++ b/crates/hir_ty/src/diagnostics/match_check/usefulness.rs
@@ -295,6 +295,7 @@ pub(crate) struct MatchCheckCtx<'a> {
     pub(crate) db: &'a dyn HirDatabase,
     /// Lowered patterns from arms plus generated by the check.
     pub(crate) pattern_arena: &'a RefCell<PatternArena>,
+    pub(crate) eprint_panic_context: &'a dyn Fn(),
 }
 
 impl<'a> MatchCheckCtx<'a> {
@@ -327,6 +328,12 @@ impl<'a> MatchCheckCtx<'a> {
     pub(super) fn type_of(&self, pat: PatId) -> Ty {
         self.pattern_arena.borrow()[pat].ty.clone()
     }
+
+    #[track_caller]
+    pub(super) fn bug(&self, info: &str) -> ! {
+        (self.eprint_panic_context)();
+        panic!("bug: {}", info);
+    }
 }
 
 #[derive(Copy, Clone)]
@@ -737,7 +744,7 @@ impl SubPatSet {
                 }
                 Seq { subpats: new_subpats }
             }
-            Alt { .. } => panic!("bug"),
+            Alt { .. } => panic!("bug"), // `self` is a patstack
         }
     }