From d95450421ee3b7cebfb18ce1312310d6c703431c Mon Sep 17 00:00:00 2001
From: Douglas Gregor <dgregor@apple.com>
Date: Thu, 9 Dec 2010 00:06:27 +0000
Subject: [PATCH] A typename specifier can end up referring to a unresolved
 using declaration that is a value in ill-formed code. Instead of crashing,
 treat this as a dependent typename specifier and suggest that the using add
 "typename" into the using declaration. Fixes <rdar://problem/8740998>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@121322 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/Basic/DiagnosticSemaKinds.td |  5 +++++
 lib/Sema/SemaTemplate.cpp                  | 19 ++++++++++++++++++-
 test/SemaTemplate/typename-specifier-4.cpp | 20 ++++++++++++++++++++
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 01e7962ac6..55270b0116 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1782,6 +1782,11 @@ def err_typename_missing : Error<
   "missing 'typename' prior to dependent type name '%0%1'">;
 def ext_typename_outside_of_template : ExtWarn<
   "'typename' occurs outside of a template">, InGroup<CXX0x>;
+def err_typename_refers_to_using_value_decl : Error<
+  "typename specifier refers to a dependent using declaration for a value "
+  "%0 in %1">;
+def note_using_value_decl_missing_typename : Note<
+  "add 'typename' to treat this using declaration as a type">;
 
 def err_template_kw_refers_to_non_template : Error<
     "%0 following the 'template' keyword does not refer to a template">;
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index 29f77f333d..5d3b75ede4 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -5699,6 +5699,23 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
   case LookupResult::NotFound:
     DiagID = diag::err_typename_nested_not_found;
     break;
+
+  case LookupResult::FoundUnresolvedValue: {
+    // We found a using declaration that is a value. Most likely, the using
+    // declaration itself is meant to have the 'typename' keyword.
+    SourceRange FullRange(KeywordLoc.isValid() ? KeywordLoc : NNSRange.getBegin(),
+                          IILoc);
+    Diag(IILoc, diag::err_typename_refers_to_using_value_decl)
+      << Name << Ctx << FullRange;
+    if (UnresolvedUsingValueDecl *Using
+          = dyn_cast<UnresolvedUsingValueDecl>(Result.getRepresentativeDecl())){
+      SourceLocation Loc = Using->getTargetNestedNameRange().getBegin();
+      Diag(Loc, diag::note_using_value_decl_missing_typename)
+        << FixItHint::CreateInsertion(Loc, "typename ");
+    }
+  }
+  // Fall through to create a dependent typename type, from which we can recover
+  // better.
       
   case LookupResult::NotFoundInCurrentInstantiation:
     // Okay, it's a member of an unknown instantiation.
@@ -5716,7 +5733,7 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
     Referenced = Result.getFoundDecl();
     break;
 
-  case LookupResult::FoundUnresolvedValue:
+    
     llvm_unreachable("unresolved using decl in non-dependent context");
     return QualType();
 
diff --git a/test/SemaTemplate/typename-specifier-4.cpp b/test/SemaTemplate/typename-specifier-4.cpp
index f5bc7477dd..38045e0a31 100644
--- a/test/SemaTemplate/typename-specifier-4.cpp
+++ b/test/SemaTemplate/typename-specifier-4.cpp
@@ -134,3 +134,23 @@ namespace PR7419 {
   template <typename T> typename T::Y::Z::W *S<T>::f() { }
   template <typename T> typename T::template Y<int>::template Z<float>::template W<double> S<T>::g() { }
 }
+
+namespace rdar8740998 {
+  template<typename T>
+  struct X : public T {
+    using T::iterator; // expected-note{{add 'typename' to treat this using declaration as a type}} \
+    // expected-error{{dependent using declaration resolved to type without 'typename'}}
+
+    void f() {
+      typename X<T>::iterator i; // expected-error{{typename specifier refers to a dependent using declaration for a value 'iterator' in 'X<T>'}}
+    }
+  };
+
+  struct HasIterator {
+    typedef int *iterator; // expected-note{{target of using declaration}}
+  };
+
+  void test_X(X<HasIterator> xi) { // expected-note{{in instantiation of template class}}
+    xi.f();
+  }
+}
-- 
2.40.0