C++ doesn't really use "namespaces" for different kinds of names the same

way that C does.  Among other differences, elaborated type specifiers
are defined to skip "non-types", which, as you might imagine, does not
include typedefs.  Rework our use of IDNS masks to capture the semantics
of different kinds of declarations better, and remove most current lookup
filters.  Removing the last remaining filter is more complicated and will
happen in a separate patch.

Fixes PR 6885 as well some spectrum of unfiled bugs.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@102164 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 71 insertions, 34 deletions

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index c9001f1030..e0ca252b06 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -5000,7 +5000,8 @@ Sema::DeclPtrTy Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
       SearchDC = SearchDC->getEnclosingNamespaceContext();
     }
 
-    // In C++, look for a shadow friend decl.
+    // In C++, we need to do a redeclaration lookup to properly
+    // diagnose some problems.
     if (getLangOptions().CPlusPlus) {
       Previous.setRedeclarationKind(ForRedeclaration);
       LookupQualifiedName(Previous, SearchDC);
@@ -5009,6 +5010,26 @@ Sema::DeclPtrTy Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
 
   if (!Previous.empty()) {
     NamedDecl *PrevDecl = (*Previous.begin())->getUnderlyingDecl();
+
+    // It's okay to have a tag decl in the same scope as a typedef
+    // which shadows a tag decl in the same scope.  Finding this
+    // insanity with a redeclaration lookup can only actually happen
+    // in C++.
+    if (getLangOptions().CPlusPlus &&
+        TUK != TUK_Reference && TUK != TUK_Friend) {
+      if (TypedefDecl *TD = dyn_cast<TypedefDecl>(PrevDecl)) {
+        if (const TagType *TT = TD->getUnderlyingType()->getAs<TagType>()) {
+          TagDecl *Tag = TT->getDecl();
+          if (Tag->getDeclName() == Name &&
+              Tag->getDeclContext()->Equals(SearchDC)) {
+            PrevDecl = Tag;
+            Previous.clear();
+            Previous.addDecl(Tag);
+          }
+        }
+      }
+    }
+
     if (TagDecl *PrevTagDecl = dyn_cast<TagDecl>(PrevDecl)) {
       // If this is a use of a previous tag, or if the tag is already declared
       // in the same scope (so that the definition/declaration completes or
@@ -5100,23 +5121,61 @@ Sema::DeclPtrTy Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
       // If we get here, we're going to create a new Decl. If PrevDecl
       // is non-NULL, it's a definition of the tag declared by
       // PrevDecl. If it's NULL, we have a new definition.
+
+
+    // Otherwise, PrevDecl is not a tag, but was found with tag
+    // lookup.  This is only actually possible in C++, where a few
+    // things like templates still live in the tag namespace.
     } else {
-      // PrevDecl is a namespace, template, or anything else
-      // that lives in the IDNS_Tag identifier namespace.
-      if (TUK == TUK_Reference || TUK == TUK_Friend ||
-          isDeclInScope(PrevDecl, SearchDC, S)) {
-        // The tag name clashes with a namespace name, issue an error and
-        // recover by making this tag be anonymous.
+      assert(getLangOptions().CPlusPlus);
+
+      // Use a better diagnostic if an elaborated-type-specifier
+      // found the wrong kind of type on the first
+      // (non-redeclaration) lookup.
+      if ((TUK == TUK_Reference || TUK == TUK_Friend) &&
+          !Previous.isForRedeclaration()) {
+        unsigned Kind = 0;
+        if (isa<TypedefDecl>(PrevDecl)) Kind = 1;
+        else if (isa<ClassTemplateDecl>(PrevDecl)) Kind = 2;
+        Diag(NameLoc, diag::err_tag_reference_non_tag) << Kind;
+        Diag(PrevDecl->getLocation(), diag::note_declared_at);
+        Invalid = true;
+
+      // Otherwise, only diagnose if the declaration is in scope.
+      } else if (!isDeclInScope(PrevDecl, SearchDC, S)) {
+        // do nothing
+
+      // Diagnose implicit declarations introduced by elaborated types.
+      } else if (TUK == TUK_Reference || TUK == TUK_Friend) {
+        unsigned Kind = 0;
+        if (isa<TypedefDecl>(PrevDecl)) Kind = 1;
+        else if (isa<ClassTemplateDecl>(PrevDecl)) Kind = 2;
+        Diag(NameLoc, diag::err_tag_reference_conflict) << Kind;
+        Diag(PrevDecl->getLocation(), diag::note_previous_decl) << PrevDecl;
+        Invalid = true;
+
+      // Otherwise it's a declaration.  Call out a particularly common
+      // case here.
+      } else if (isa<TypedefDecl>(PrevDecl)) {
+        Diag(NameLoc, diag::err_tag_definition_of_typedef)
+          << Name
+          << cast<TypedefDecl>(PrevDecl)->getUnderlyingType();
+        Diag(PrevDecl->getLocation(), diag::note_previous_decl) << PrevDecl;
+        Invalid = true;
+
+      // Otherwise, diagnose.
+      } else {
+        // The tag name clashes with something else in the target scope,
+        // issue an error and recover by making this tag be anonymous.
         Diag(NameLoc, diag::err_redefinition_different_kind) << Name;
         Diag(PrevDecl->getLocation(), diag::note_previous_definition);
         Name = 0;
-        Previous.clear();
         Invalid = true;
-      } else {
-        // The existing declaration isn't relevant to us; we're in a
-        // new scope, so clear out the previous declaration.
-        Previous.clear();
       }
+
+      // The existing declaration isn't relevant to us; we're in a
+      // new scope, so clear out the previous declaration.
+      Previous.clear();
     }
   }
 
@@ -5187,28 +5246,6 @@ CreateNewDecl:
       New->addAttr(::new (Context) PragmaPackAttr(Alignment * 8));
   }
 
-  if (getLangOptions().CPlusPlus && SS.isEmpty() && Name && !Invalid) {
-    // C++ [dcl.typedef]p3:
-    //   [...] Similarly, in a given scope, a class or enumeration
-    //   shall not be declared with the same name as a typedef-name
-    //   that is declared in that scope and refers to a type other
-    //   than the class or enumeration itself.
-    LookupResult Lookup(*this, Name, NameLoc, LookupOrdinaryName,
-                        ForRedeclaration);
-    LookupName(Lookup, S);
-    TypedefDecl *PrevTypedef = Lookup.getAsSingle<TypedefDecl>();
-    NamedDecl *PrevTypedefNamed = PrevTypedef;
-    if (PrevTypedef && isDeclInScope(PrevTypedefNamed, SearchDC, S) &&
-        Context.getCanonicalType(Context.getTypeDeclType(PrevTypedef)) !=
-          Context.getCanonicalType(Context.getTypeDeclType(New))) {
-      Diag(Loc, diag::err_tag_definition_of_typedef)
-        << Context.getTypeDeclType(New)
-        << PrevTypedef->getUnderlyingType();
-      Diag(PrevTypedef->getLocation(), diag::note_previous_definition);
-      Invalid = true;
-    }
-  }
-
   // If this is a specialization of a member class (of a class template),
   // check the specialization.
   if (isExplicitSpecialization && CheckMemberSpecialization(New, Previous))