1 files changed, 23 insertions, 8 deletions
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 33d73bf106..b8d58c101c 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -1929,18 +1929,33 @@ bool Sema::CheckCastTypes(SourceRange TyR, QualType castType, Expr *&castExpr) {
   } else if (castType->isDependentType() || castExpr->isTypeDependent()) {
     // We can't check any more until template instantiation time.
   } else if (!castType->isScalarType() && !castType->isVectorType()) {
-    // GCC struct/union extension: allow cast to self.
-    if (Context.getCanonicalType(castType).getUnqualifiedType() !=
-        Context.getCanonicalType(castExpr->getType().getUnqualifiedType()) ||
-        (!castType->isStructureType() && !castType->isUnionType())) {
+    if (Context.getCanonicalType(castType).getUnqualifiedType() ==
+        Context.getCanonicalType(castExpr->getType().getUnqualifiedType()) &&
+        (castType->isStructureType() || castType->isUnionType())) {
+      // GCC struct/union extension: allow cast to self.
+      Diag(TyR.getBegin(), diag::ext_typecheck_cast_nonscalar)
+        << castType << castExpr->getSourceRange();
+    } else if (castType->isUnionType()) {
+      // GCC cast to union extension
+      RecordDecl *RD = castType->getAsRecordType()->getDecl();
+      RecordDecl::field_iterator Field, FieldEnd;
+      for (Field = RD->field_begin(), FieldEnd = RD->field_end();
+           Field != FieldEnd; ++Field) {
+        if (Context.getCanonicalType(Field->getType()).getUnqualifiedType() ==
+            Context.getCanonicalType(castExpr->getType()).getUnqualifiedType()) {
+          Diag(TyR.getBegin(), diag::ext_typecheck_cast_to_union)
+            << castExpr->getSourceRange();
+          break;
+        }
+      }
+      if (Field == FieldEnd)
+        return Diag(TyR.getBegin(), diag::err_typecheck_cast_to_union_no_type)
+          << castExpr->getType() << castExpr->getSourceRange();
+    } else {
       // Reject any other conversions to non-scalar types.
       return Diag(TyR.getBegin(), diag::err_typecheck_cond_expect_scalar)
         << castType << castExpr->getSourceRange();
     }
-      
-    // accept this, but emit an ext-warn.
-    Diag(TyR.getBegin(), diag::ext_typecheck_cast_nonscalar)
-      << castType << castExpr->getSourceRange();
   } else if (!castExpr->getType()->isScalarType() && 
              !castExpr->getType()->isVectorType()) {
     return Diag(castExpr->getLocStart(),