Sema: Handle declspecs without declarators in records properly in C mode

We had two bugs:
- We wouldn't properly warn when a struct/union/enum was mentioned
  inside of a record definition if no declarator was provided.  We
  should have mentioned that this declaration declares nothing.
- We didn't properly support Microsoft's extension where certain
  declspecs without declarators would act as anonymous structs/unions.
  * We completely ignored the case where such a declspec could be a
    union.
  * We didn't properly handle the case where a record was defined inside
    another record:
      struct X {
        int a;
        struct Y {
          int b;
        };
      };

llvm-svn: 215347

1 files changed, 28 insertions, 16 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 85c88a3f576..53a647149a8 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -3444,21 +3444,36 @@ Decl *Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
     }
   }
 
-  // Check for Microsoft C extension: anonymous struct member.
-  if (getLangOpts().MicrosoftExt && !getLangOpts().CPlusPlus &&
-      CurContext->isRecord() &&
+  // C11 6.7.2.1p2:
+  //   A struct-declaration that does not declare an anonymous structure or
+  //   anonymous union shall contain a struct-declarator-list.
+  if (!getLangOpts().CPlusPlus && CurContext->isRecord() &&
       DS.getStorageClassSpec() == DeclSpec::SCS_unspecified) {
-    // Handle 2 kinds of anonymous struct:
+    // Check for Microsoft C extension: anonymous struct/union member.
+    // Handle 2 kinds of anonymous struct/union:
     //   struct STRUCT;
+    //   union UNION;
     // and
     //   STRUCT_TYPE;  <- where STRUCT_TYPE is a typedef struct.
-    RecordDecl *Record = dyn_cast_or_null<RecordDecl>(Tag);
-    if ((Record && Record->getDeclName() && !Record->isCompleteDefinition()) ||
-        (DS.getTypeSpecType() == DeclSpec::TST_typename &&
-         DS.getRepAsType().get()->isStructureType())) {
-      Diag(DS.getLocStart(), diag::ext_ms_anonymous_struct)
-        << DS.getSourceRange();
-      return BuildMicrosoftCAnonymousStruct(S, DS, Record);
+    //   UNION_TYPE;   <- where UNION_TYPE is a typedef union.
+    if ((Tag && Tag->getDeclName()) ||
+        DS.getTypeSpecType() == DeclSpec::TST_typename) {
+      RecordDecl *Record = nullptr;
+      if (Tag)
+        Record = dyn_cast<RecordDecl>(Tag);
+      else if (const RecordType *RT =
+                   DS.getRepAsType().get()->getAsStructureType())
+        Record = RT->getDecl();
+      else if (const RecordType *UT = DS.getRepAsType().get()->getAsUnionType())
+        Record = UT->getDecl();
+
+      if (Record && getLangOpts().MicrosoftExt) {
+        Diag(DS.getLocStart(), diag::ext_ms_anonymous_record)
+          << Record->isUnion() << DS.getSourceRange();
+        return BuildMicrosoftCAnonymousStruct(S, DS, Record);
+      }
+
+      DeclaresAnything = false;
     }
   }
 
@@ -3999,15 +4014,12 @@ Decl *Sema::BuildAnonymousStructOrUnion(Scope *S, DeclSpec &DS,
 ///
 /// void foo() {
 ///   B var;
-///   var.a = 3; 
+///   var.a = 3;
 /// }
 ///
 Decl *Sema::BuildMicrosoftCAnonymousStruct(Scope *S, DeclSpec &DS,
                                            RecordDecl *Record) {
-  
-  // If there is no Record, get the record via the typedef.
-  if (!Record)
-    Record = DS.getRepAsType().get()->getAsStructureType()->getDecl();
+  assert(Record && "expected a record!");
 
   // Mock up a declarator.
   Declarator Dc(DS, Declarator::TypeNameContext);