3 files changed, 38 insertions, 24 deletions

diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 0f6e8b09706..8c50af615cd 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -635,6 +635,8 @@ static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D,
   if (D->isInAnonymousNamespace()) {
     const auto *Var = dyn_cast<VarDecl>(D);
     const auto *Func = dyn_cast<FunctionDecl>(D);
+    // FIXME: In C++11 onwards, anonymous namespaces should give decls
+    // within them internal linkage, not unique external linkage.
     if ((!Var || !isFirstInExternCContext(Var)) &&
         (!Func || !isFirstInExternCContext(Func)))
       return LinkageInfo::uniqueExternal();
@@ -821,10 +823,14 @@ static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D,
   } else if (isa<ObjCInterfaceDecl>(D)) {
     // fallout
 
+  } else if (auto *TD = dyn_cast<TypedefNameDecl>(D)) {
+    // A typedef declaration has linkage if it gives a type a name for
+    // linkage purposes.
+    if (!TD->getAnonDeclWithTypedefName(/*AnyRedecl*/true))
+      return LinkageInfo::none();
+
   // Everything not covered here has no linkage.
   } else {
-    // FIXME: A typedef declaration has linkage if it gives a type a name for
-    // linkage purposes.
     return LinkageInfo::none();
   }
 
@@ -1226,8 +1232,32 @@ static LinkageInfo computeLVForDecl(const NamedDecl *D,
   switch (D->getKind()) {
     default:
       break;
+
+    // Per C++ [basic.link]p2, only the names of objects, references,
+    // functions, types, templates, namespaces, and values ever have linkage.
+    //
+    // Note that the name of a typedef, namespace alias, using declaration,
+    // and so on are not the name of the corresponding type, namespace, or
+    // declaration, so they do *not* have linkage.
+    case Decl::EnumConstant: // FIXME: This has linkage, but that's dumb.
+    case Decl::ImplicitParam:
+    case Decl::Label:
+    case Decl::NamespaceAlias:
     case Decl::ParmVar:
+    case Decl::Using:
+    case Decl::UsingShadow:
+    case Decl::UsingDirective:
       return LinkageInfo::none();
+
+    case Decl::Typedef:
+    case Decl::TypeAlias:
+      // A typedef declaration has linkage if it gives a type a name for
+      // linkage purposes.
+      if (!cast<TypedefNameDecl>(D)
+               ->getAnonDeclWithTypedefName(/*AnyRedecl*/true))
+        return LinkageInfo::none();
+      break;
+
     case Decl::TemplateTemplateParm: // count these as external
     case Decl::NonTypeTemplateParm:
     case Decl::ObjCAtDefsField:
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 728697e78f5..a23d9debb86 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -4819,12 +4819,6 @@ NamedDecl *Sema::HandleDeclarator(Scope *S, Declarator &D,
   LookupResult Previous(*this, NameInfo, LookupOrdinaryName,
                         ForRedeclaration);
 
-  // If we're hiding internal-linkage symbols in modules from redeclaration
-  // lookup, let name lookup know.
-  if ((getLangOpts().Modules || getLangOpts().ModulesLocalVisibility) &&
-      D.getDeclSpec().getStorageClassSpec() != DeclSpec::SCS_typedef)
-    Previous.setAllowHiddenInternal(false);
-
   // See if this is a redefinition of a variable in the same scope.
   if (!D.getCXXScopeSpec().isSet()) {
     bool IsLinkageLookup = false;
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 74bffb2a044..910ebcf05dd 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -7206,23 +7206,13 @@ Decl *Sema::ActOnStartNamespaceDef(Scope *NamespcScope,
     //   treated as an original-namespace-name.
     //
     // Since namespace names are unique in their scope, and we don't
-    // look through using directives, just look for any ordinary names.
-    
-    const unsigned IDNS = Decl::IDNS_Ordinary | Decl::IDNS_Member | 
-    Decl::IDNS_Type | Decl::IDNS_Using | Decl::IDNS_Tag | 
-    Decl::IDNS_Namespace;
-    NamedDecl *PrevDecl = nullptr;
-    DeclContext::lookup_result R = CurContext->getRedeclContext()->lookup(II);
-    for (DeclContext::lookup_iterator I = R.begin(), E = R.end(); I != E;
-         ++I) {
-      if ((*I)->getIdentifierNamespace() & IDNS) {
-        PrevDecl = *I;
-        break;
-      }
-    }
-    
+    // look through using directives, just look for any ordinary names
+    // as if by qualified name lookup.
+    LookupResult R(*this, II, IdentLoc, LookupOrdinaryName, ForRedeclaration);
+    LookupQualifiedName(R, CurContext->getRedeclContext());
+    NamedDecl *PrevDecl = R.getAsSingle<NamedDecl>();
     PrevNS = dyn_cast_or_null<NamespaceDecl>(PrevDecl);
-    
+
     if (PrevNS) {
       // This is an extended namespace definition.
       if (IsInline != PrevNS->isInline())