The code trying to assign a typedef to an anonymous tag declaration was

extremely rambunctious, both on parsing and on template instantiation.
Calm it down, fixing an internal consistency assert on anonymous enum
instantiation manglings.

llvm-svn: 124653

clang/lib/Sema/SemaDecl.cpp

@@ -5697,17 +5697,46 @@ TypedefDecl *Sema::ParseTypedefDecl(Scope *S, Declarator &D, QualType T,
                                            D.getIdentifier(),
                                            TInfo);
 
-  if (const TagType *TT = T->getAs<TagType>()) {
-    TagDecl *TD = TT->getDecl();
-
-    // If the TagDecl that the TypedefDecl points to is an anonymous decl
-    // keep track of the TypedefDecl.
-    if (!TD->getIdentifier() && !TD->getTypedefForAnonDecl())
-      TD->setTypedefForAnonDecl(NewTD);
+  // Bail out immediately if we have an invalid declaration.
+  if (D.isInvalidType()) {
+    NewTD->setInvalidDecl();
+    return NewTD;
+  }
+
+  // C++ [dcl.typedef]p8:
+  //   If the typedef declaration defines an unnamed class (or
+  //   enum), the first typedef-name declared by the declaration
+  //   to be that class type (or enum type) is used to denote the
+  //   class type (or enum type) for linkage purposes only.
+  // We need to check whether the type was declared in the declaration.
+  switch (D.getDeclSpec().getTypeSpecType()) {
+  case TST_enum:
+  case TST_struct:
+  case TST_union:
+  case TST_class: {
+    TagDecl *tagFromDeclSpec = cast<TagDecl>(D.getDeclSpec().getRepAsDecl());
+
+    // Do nothing if the tag is not anonymous or already has an
+    // associated typedef (from an earlier typedef in this decl group).
+    if (tagFromDeclSpec->getIdentifier()) break;
+    if (tagFromDeclSpec->getTypedefForAnonDecl()) break;
+
+    // A well-formed anonymous tag must always be a TUK_Definition.
+    assert(tagFromDeclSpec->isThisDeclarationADefinition());
+
+    // The type must match the tag exactly;  no qualifiers allowed.
+    if (!Context.hasSameType(T, Context.getTagDeclType(tagFromDeclSpec)))
+      break;
+
+    // Otherwise, set this is the anon-decl typedef for the tag.
+    tagFromDeclSpec->setTypedefForAnonDecl(NewTD);
+    break;
+  }
+    
+  default:
+    break;
   }
 
-  if (D.isInvalidType())
-    NewTD->setInvalidDecl();
   return NewTD;
 }
 

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -143,13 +143,15 @@ Decl *TemplateDeclInstantiator::VisitTypedefDecl(TypedefDecl *D) {
   if (Invalid)
     Typedef->setInvalidDecl();
 
-  if (const TagType *TT = DI->getType()->getAs<TagType>()) {
-    TagDecl *TD = TT->getDecl();
-    
-    // If the TagDecl that the TypedefDecl points to is an anonymous decl
-    // keep track of the TypedefDecl.
-    if (!TD->getIdentifier() && !TD->getTypedefForAnonDecl())
-      TD->setTypedefForAnonDecl(Typedef);
+  // If the old typedef was the name for linkage purposes of an anonymous
+  // tag decl, re-establish that relationship for the new typedef.
+  if (const TagType *oldTagType = D->getUnderlyingType()->getAs<TagType>()) {
+    TagDecl *oldTag = oldTagType->getDecl();
+    if (oldTag->getTypedefForAnonDecl() == D) {
+      TagDecl *newTag = DI->getType()->castAs<TagType>()->getDecl();
+      assert(!newTag->getIdentifier() && !newTag->getTypedefForAnonDecl());
+      newTag->setTypedefForAnonDecl(Typedef);
+    }
   }
   
   if (TypedefDecl *Prev = D->getPreviousDeclaration()) {

clang/test/CodeGenCXX/mangle-unnamed.cpp

@@ -69,3 +69,14 @@ int f7() {
   // CHECK: _ZZ2f7vE1a
   return a.b;
 }
+
+// This used to cause an assert because the typedef-for-anonymous-tag
+// code was trying to claim the enum for the template.
+enum { T8 };
+template <class T> struct Test8 {
+  typedef T type;
+  // define internal void @"_ZN5Test8I3$_2EC1ES0_"(
+  Test8(type t) {}
+};
+template <class T> void make_test8(T value) { Test8<T> t(value); }
+void test8() { make_test8(T8); }