1 files changed, 19 insertions, 4 deletions
diff --git a/compiler/rustc_mir_build/src/check_unsafety.rs b/compiler/rustc_mir_build/src/check_unsafety.rs
index c7fcfe3ce2a..4fe984b961e 100644
--- a/compiler/rustc_mir_build/src/check_unsafety.rs
+++ b/compiler/rustc_mir_build/src/check_unsafety.rs
@@ -218,6 +218,13 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
                 warnings: self.warnings,
                 suggest_unsafe_block: self.suggest_unsafe_block,
             };
+            // params in THIR may be unsafe, e.g. a union pattern.
+            for param in &inner_thir.params {
+                if let Some(param_pat) = param.pat.as_deref() {
+                    inner_visitor.visit_pat(param_pat);
+                }
+            }
+            // Visit the body.
             inner_visitor.visit_expr(&inner_thir[expr]);
             // Unsafe blocks can be used in the inner body, make sure to take it into account
             self.safety_context = inner_visitor.safety_context;
@@ -315,14 +322,15 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                 | PatKind::DerefPattern { .. }
                 | PatKind::Range { .. }
                 | PatKind::Slice { .. }
-                | PatKind::Array { .. } => {
+                | PatKind::Array { .. }
+                // Never constitutes a witness of uninhabitedness.
+                | PatKind::Never => {
                     self.requires_unsafe(pat.span, AccessToUnionField);
                     return; // we can return here since this already requires unsafe
                 }
-                // wildcard/never don't take anything
+                // wildcard doesn't read anything.
                 PatKind::Wild |
-                PatKind::Never |
-                // these just wrap other patterns
+                // these just wrap other patterns, which we recurse on below.
                 PatKind::Or { .. } |
                 PatKind::InlineConstant { .. } |
                 PatKind::AscribeUserType { .. } |
@@ -1032,6 +1040,13 @@ pub(crate) fn check_unsafety(tcx: TyCtxt<'_>, def: LocalDefId) {
         warnings: &mut warnings,
         suggest_unsafe_block: true,
     };
+    // params in THIR may be unsafe, e.g. a union pattern.
+    for param in &thir.params {
+        if let Some(param_pat) = param.pat.as_deref() {
+            visitor.visit_pat(param_pat);
+        }
+    }
+    // Visit the body.
     visitor.visit_expr(&thir[expr]);
 
     warnings.sort_by_key(|w| w.block_span);