[AST][RecoveryAST] Avoid spurious 'missing typename' diagnostic when the NNS contains errors.

[sammccall]

clang/test/SemaTemplate/missing-typename-recovery.cpp

1

nit: name of this test seems slightly unusual, maybe just nns-recovery.cpp or something like this?

[hokein]

rename the test file.

clang/include/clang/AST/NestedNameSpecifier.h

public:
   /// Whether this nested name specifier involves a template
   /// parameter.
   bool isInstantiationDependent() const;
 
   /// Whether this nested-name-specifier contains an unexpanded
   /// parameter pack (for C++11 variadic templates).
   bool containsUnexpandedParameterPack() const;
 
+  /// Whether this nested name specifier contains an error.
+  bool containsErrors() const;
+
   /// Print this nested name specifier to the given output stream. If
   /// `ResolveTemplateArguments` is true, we'll print actual types, e.g.
   /// `ns::SomeTemplate<int, MyClass>` instead of
   /// `ns::SomeTemplate<Container::value_type, T>`.
   void print(raw_ostream &OS, const PrintingPolicy &Policy,
              bool ResolveTemplateArguments = false) const;
 
   void Profile(llvm::FoldingSetNodeID &ID) const {

clang/lib/AST/NestedNameSpecifier.cpp

 bool NestedNameSpecifier::isInstantiationDependent() const {
   return getDependence() & NestedNameSpecifierDependence::Instantiation;
 }
 
 bool NestedNameSpecifier::containsUnexpandedParameterPack() const {
   return getDependence() & NestedNameSpecifierDependence::UnexpandedPack;
 }
 
+bool NestedNameSpecifier::containsErrors() const {
+  return getDependence() & NestedNameSpecifierDependence::Error;
+}
+
 /// Print this nested name specifier to the given output
 /// stream.
 void NestedNameSpecifier::print(raw_ostream &OS, const PrintingPolicy &Policy,
                                 bool ResolveTemplateArguments) const {
   if (getPrefix())
     getPrefix()->print(OS, Policy);
 
   switch (getKind()) {

clang/lib/Sema/SemaDecl.cpp

void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
   if (!SS || (!SS->isSet() && !SS->isInvalid()))
     Diag(IILoc, IsTemplateName ? diag::err_no_template
                                : diag::err_unknown_typename)
         << II;
   else if (DeclContext *DC = computeDeclContext(*SS, false))
     Diag(IILoc, IsTemplateName ? diag::err_no_member_template
                                : diag::err_typename_nested_not_found)
         << II << DC << SS->getRange();
-  else if (isDependentScopeSpecifier(*SS)) {
+  else if (SS->isValid() && SS->getScopeRep()->containsErrors()) {
+    SuggestedType =
+        ActOnTypenameType(S, SourceLocation(), *SS, *II, IILoc).get();
+  } else if (isDependentScopeSpecifier(*SS)) {
     unsigned DiagID = diag::err_typename_missing;
     if (getLangOpts().MSVCCompat && isMicrosoftMissingTypename(SS, S))
       DiagID = diag::ext_typename_missing;
 
     Diag(SS->getRange().getBegin(), DiagID)
       << SS->getScopeRep() << II->getName()
       << SourceRange(SS->getRange().getBegin(), IILoc)
       << FixItHint::CreateInsertion(SS->getRange().getBegin(), "typename ");

clang/test/SemaTemplate/missing-typename-recovery.cpp

+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+// There should be no extra errors about missing 'typename' keywords.
+void f() {
+  decltype(undef())::Type T; // expected-error {{use of undeclared identifier}}
+}