[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

2 files changed, 61 insertions, 0 deletions

diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
index 452ff6201a2..02943ccef90 100644
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -22,6 +22,7 @@
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/NestedNameSpecifier.h"
+#include "clang/AST/NonTrivialTypeVisitor.h"
 #include "clang/AST/PrettyPrinter.h"
 #include "clang/AST/TemplateBase.h"
 #include "clang/AST/TemplateName.h"
@@ -2244,6 +2245,62 @@ bool QualType::isNonWeakInMRRWithObjCWeak(const ASTContext &Context) const {
          getObjCLifetime() != Qualifiers::OCL_Weak;
 }
 
+namespace {
+// Helper class that determines whether this is a type that is non-trivial to
+// primitive copy or move, or is a struct type that has a field of such type.
+template <bool IsMove>
+struct IsNonTrivialCopyMoveVisitor
+    : CopiedTypeVisitor<IsNonTrivialCopyMoveVisitor<IsMove>, IsMove, bool> {
+  using Super =
+      CopiedTypeVisitor<IsNonTrivialCopyMoveVisitor<IsMove>, IsMove, bool>;
+  IsNonTrivialCopyMoveVisitor(const ASTContext &C) : Ctx(C) {}
+  void preVisit(QualType::PrimitiveCopyKind PCK, QualType QT) {}
+
+  bool visitWithKind(QualType::PrimitiveCopyKind PCK, QualType QT) {
+    if (const auto *AT = this->Ctx.getAsArrayType(QT))
+      return this->asDerived().visit(QualType(AT, 0));
+    return Super::visitWithKind(PCK, QT);
+  }
+
+  bool visitARCStrong(QualType QT) { return true; }
+  bool visitARCWeak(QualType QT) { return true; }
+  bool visitTrivial(QualType QT) { return false; }
+  // Volatile fields are considered trivial.
+  bool visitVolatileTrivial(QualType QT) { return false; }
+
+  bool visitStruct(QualType QT) {
+    const RecordDecl *RD = QT->castAs<RecordType>()->getDecl();
+    // We don't want to apply the C restriction in C++ because C++
+    // (1) can apply the restriction at a finer grain by banning copying or
+    //     destroying the union, and
+    // (2) allows users to override these restrictions by declaring explicit
+    //     constructors/etc, which we're not proposing to add to C.
+    if (isa<CXXRecordDecl>(RD))
+      return false;
+    for (const FieldDecl *FD : RD->fields())
+      if (this->asDerived().visit(FD->getType()))
+        return true;
+    return false;
+  }
+
+  const ASTContext &Ctx;
+};
+
+} // namespace
+
+bool QualType::isNonTrivialPrimitiveCType(const ASTContext &Ctx) const {
+  if (isNonTrivialToPrimitiveDefaultInitialize())
+    return true;
+  DestructionKind DK = isDestructedType();
+  if (DK != DK_none && DK != DK_cxx_destructor)
+    return true;
+  if (IsNonTrivialCopyMoveVisitor<false>(Ctx).visit(*this))
+    return true;
+  if (IsNonTrivialCopyMoveVisitor<true>(Ctx).visit(*this))
+    return true;
+  return false;
+}
+
 QualType::PrimitiveDefaultInitializeKind
 QualType::isNonTrivialToPrimitiveDefaultInitialize() const {
   if (const auto *RT =
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)