[Sema] Fix a miscompile by retaining array qualifiers when folding VLAs to constant arrays

[erik.pilkington]

Summary

Fixes rdar://72243125.

[arphaman]

Thanks!

clang/lib/Sema/SemaDecl.cpp

unsigned ActiveSizeBits =
        !ElemTy->isIncompleteType() && !ElemTy->isUndeducedType())
           ? ConstantArrayType::getNumAddressingBits(Context, ElemTy, Res)
           : Res.getActiveBits();
   if (ActiveSizeBits > ConstantArrayType::getMaxSizeBits(Context)) {
     Oversized = Res;
     return QualType();
   }
 
-  return Context.getConstantArrayType(ElemTy, Res, VLATy->getSizeExpr(),
-                                      ArrayType::Normal, 0);
+  QualType FoldedArrayType = Context.getConstantArrayType(
+      ElemTy, Res, VLATy->getSizeExpr(), ArrayType::Normal, 0);
+  return Qs.apply(Context, FoldedArrayType);
 }
 
 static void
 FixInvalidVariablyModifiedTypeLoc(TypeLoc SrcTL, TypeLoc DstTL) {
   SrcTL = SrcTL.getUnqualifiedLoc();
   DstTL = DstTL.getUnqualifiedLoc();
   if (PointerTypeLoc SrcPTL = SrcTL.getAs<PointerTypeLoc>()) {
     PointerTypeLoc DstPTL = DstTL.castAs<PointerTypeLoc>();

clang/test/SemaObjC/arc.m

^{
     (void)*g;
     (void)*h; // expected-warning {{block captures an autoreleasing out-parameter, which may result in use-after-free bugs}}
     (void)*i; // expected-warning {{block captures an autoreleasing out-parameter, which may result in use-after-free bugs}}
     (void)*j;
     (void)*k; // expected-warning {{block captures an autoreleasing out-parameter, which may result in use-after-free bugs}}
     (void)*l;
   }();
 }
+
+void test_vla_fold_keeps_strong(void) {
+  const unsigned bounds = 1;
+
+  static id array[bounds]; // expected-warning {{variable length array folded to constant array as an extension}}
+  typedef __typeof__(array) array_type;
+  typedef id __strong array_type[1];
+
+  static id weak_array[bounds] __weak; // expected-warning {{variable length array folded to constant array as an extension}}
+  typedef __typeof__(weak_array) weak_array_type;
+  typedef id __weak weak_array_type[1];
+}