[Sema][ObjC] Disallow non-trivial C struct fields in unions.

This patch fixes a bug where clang doesn’t reject union fields of
non-trivial C struct types. For example:

```
// This struct is non-trivial under ARC.
struct S0 {
  id x;
};

union U0 {
  struct S0 s0; // clang should reject this.
  struct S0 s1; // clang should reject this.
};

void test(union U0 a) {
  // Previously, both 'a.s0.x' and 'a.s1.x' were released in this
  // function.
}
```

rdar://problem/46677858

Differential Revision: https://reviews.llvm.org/D55659

llvm-svn: 353459

1 files changed, 4 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index c8a69c4d537..a9e6eb12c0d 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -15916,6 +15916,10 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
         Record->setHasObjectMember(true);
       if (Record && FDTTy->getDecl()->hasVolatileMember())
         Record->setHasVolatileMember(true);
+      if (Record && Record->isUnion() &&
+          FD->getType().isNonTrivialPrimitiveCType(Context))
+        Diag(FD->getLocation(),
+             diag::err_nontrivial_primitive_type_in_union);
     } else if (FDTy->isObjCObjectType()) {
       /// A field cannot be an Objective-c object
       Diag(FD->getLocation(), diag::err_statically_allocated_object)