[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, 17 insertions, 1 deletions

diff --git a/clang/test/SemaObjC/arc-decls.m b/clang/test/SemaObjC/arc-decls.m
index c728f00c7e5..0abd45dac33 100644
--- a/clang/test/SemaObjC/arc-decls.m
+++ b/clang/test/SemaObjC/arc-decls.m
@@ -3,13 +3,29 @@
 // rdar://8843524
 
 struct A {
-    id x;
+  id x[4];
+  id y;
 };
 
 union u {
     id u; // expected-error {{ARC forbids Objective-C objects in union}}
 };
 
+union u_nontrivial_c {
+  struct A a; // expected-error {{non-trivial C types are disallowed in union}}
+};
+
+// Volatile fields are fine.
+struct C {
+  volatile int x[4];
+  volatile int y;
+};
+
+union u_trivial_c {
+  volatile int b;
+  struct C c;
+};
+
 @interface I {
    struct A a; 
    struct B {