From 77faa365cb2322cfc8edf58a4f5d68f2370cc39a Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Wed, 19 Oct 2011 00:07:01 +0000
Subject: [PATCH] -Wc++98-compat: warn if a SFINAE substitution in C++11
 suppresses an access control diagnostic.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@142463 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/Basic/Diagnostic.h           |  5 +++
 include/clang/Basic/DiagnosticSemaKinds.td |  3 ++
 lib/Sema/Sema.cpp                          | 38 ++++++++++++++++------
 test/SemaCXX/cxx98-compat.cpp              |  9 +++++
 4 files changed, 45 insertions(+), 10 deletions(-)

diff --git a/include/clang/Basic/Diagnostic.h b/include/clang/Basic/Diagnostic.h
index ae0f6ea0cf..7dde271c38 100644
--- a/include/clang/Basic/Diagnostic.h
+++ b/include/clang/Basic/Diagnostic.h
@@ -740,6 +740,11 @@ public:
     assert(isActive() && "DiagnosticsEngine is inactive");
     return DiagObj->CurDiagID;
   }
+
+  /// \brief Retrieve the active diagnostic's location.
+  ///
+  /// \pre \c isActive()
+  SourceLocation getLocation() const { return DiagObj->CurDiagLoc; }
   
   /// \brief Clear out the current diagnostic.
   void Clear() { DiagObj = 0; }
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 8d8a888e7e..5c4ecc8f9d 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -808,6 +808,9 @@ def note_access_constrained_by_path : Note<
   " inheritance here">;
 def note_access_protected_restricted : Note<
   "object type %select{|%1 }0must derive from context type %2">;
+def warn_cxx98_compat_sfinae_access_control : Warning<
+  "substitution failure due to access control is incompatible with C++98">,
+  InGroup<CXX98Compat>, DefaultIgnore, NoSFINAE;
   
 // C++ name lookup
 def err_incomplete_nested_name_spec : Error<
diff --git a/lib/Sema/Sema.cpp b/lib/Sema/Sema.cpp
index 4a9d8a5efb..8346cc475f 100644
--- a/lib/Sema/Sema.cpp
+++ b/lib/Sema/Sema.cpp
@@ -625,18 +625,9 @@ Sema::SemaDiagnosticBuilder::~SemaDiagnosticBuilder() {
   if (llvm::Optional<TemplateDeductionInfo*> Info = SemaRef.isSFINAEContext()) {
     switch (DiagnosticIDs::getDiagnosticSFINAEResponse(getDiagID())) {
     case DiagnosticIDs::SFINAE_Report:
-      // Fall through; we'll report the diagnostic below.
+      // We'll report the diagnostic below.
       break;
       
-    case DiagnosticIDs::SFINAE_AccessControl:
-      // Per C++ Core Issue 1170, access control is part of SFINAE.
-      // Additionally, the AccessCheckingSFINAE flag can be used to temporary
-      // make access control a part of SFINAE for the purposes of checking
-      // type traits.
-      if (!SemaRef.AccessCheckingSFINAE &&
-          !SemaRef.getLangOptions().CPlusPlus0x)
-        break;
-        
     case DiagnosticIDs::SFINAE_SubstitutionFailure:
       // Count this failure so that we know that template argument deduction
       // has failed.
@@ -646,6 +637,33 @@ Sema::SemaDiagnosticBuilder::~SemaDiagnosticBuilder() {
       Clear();
       return;
       
+    case DiagnosticIDs::SFINAE_AccessControl: {
+      // Per C++ Core Issue 1170, access control is part of SFINAE.
+      // Additionally, the AccessCheckingSFINAE flag can be used to temporary
+      // make access control a part of SFINAE for the purposes of checking
+      // type traits.
+      if (!SemaRef.AccessCheckingSFINAE &&
+          !SemaRef.getLangOptions().CPlusPlus0x)
+        break;
+
+      SourceLocation Loc = getLocation();
+
+      // Suppress this diagnostic.
+      ++SemaRef.NumSFINAEErrors;
+      SemaRef.Diags.setLastDiagnosticIgnored();
+      SemaRef.Diags.Clear();
+      Clear();
+
+      // Now the diagnostic state is clear, produce a C++98 compatibility
+      // warning.
+      SemaRef.Diag(Loc, diag::warn_cxx98_compat_sfinae_access_control);
+
+      // The last diagnostic which Sema produced was ignored. Suppress any
+      // notes attached to it.
+      SemaRef.Diags.setLastDiagnosticIgnored();
+      return;
+    }
+
     case DiagnosticIDs::SFINAE_Suppress:
       // Make a copy of this suppressed diagnostic and store it with the
       // template-deduction information;
diff --git a/test/SemaCXX/cxx98-compat.cpp b/test/SemaCXX/cxx98-compat.cpp
index 84dc87ac3d..8da54f0da6 100644
--- a/test/SemaCXX/cxx98-compat.cpp
+++ b/test/SemaCXX/cxx98-compat.cpp
@@ -170,3 +170,12 @@ struct BadFriends {
 };
 
 int n = {}; // expected-warning {{scalar initialized from empty initializer list is incompatible with C++98}}
+
+class PrivateMember {
+  struct ImPrivate {};
+};
+template<typename T> typename T::ImPrivate SFINAEAccessControl(T t) { // expected-warning {{substitution failure due to access control is incompatible with C++98}} expected-note {{while substituting deduced template arguments into function template 'SFINAEAccessControl' [with T = PrivateMember]}}
+  return typename T::ImPrivate();
+}
+int SFINAEAccessControl(...) { return 0; }
+int CheckSFINAEAccessControl = SFINAEAccessControl(PrivateMember());