Patch for clang to improve sfinae errors.

pr13309.patch

Index: include/clang/Sema/TemplateDeduction.h
===================================================================
--- a/tools/clang/include/clang/Sema/TemplateDeduction.h	(revision 159968)
+++ b/tools/clang/include/clang/Sema/TemplateDeduction.h	(working copy)
@@ -39,6 +39,9 @@
   /// deduction is occurring.
   SourceLocation Loc;
 
+  /// \brief Should we suppress errors during substitution?
+  bool IsSFINAEContext;
+
   /// \brief Have we suppressed an error during deduction?
   bool HasSFINAEDiagnostic;
 
@@ -52,7 +55,8 @@
 
 public:
   TemplateDeductionInfo(ASTContext &Context, SourceLocation Loc)
-    : Context(Context), Deduced(0), Loc(Loc), HasSFINAEDiagnostic(false) { }
+    : Context(Context), Deduced(0), Loc(Loc), IsSFINAEContext(true),
+      HasSFINAEDiagnostic(false) { }
 
   ~TemplateDeductionInfo() {
     // FIXME: if (Deduced) Deduced->Destroy(Context);
@@ -87,6 +91,10 @@
     Deduced = NewDeduced;
   }
 
+  /// \brief Should we suppress errors during this deduction?
+  bool isSFINAEContext() const { return IsSFINAEContext; }
+  void setSFINAEContext(bool SFINAE) { IsSFINAEContext = SFINAE; }
+
   /// \brief Is a SFINAE diagnostic available?
   bool hasSFINAEDiagnostic() const {
     return HasSFINAEDiagnostic;
Index: lib/Sema/SemaOverload.cpp
===================================================================
--- a/tools/clang/lib/Sema/SemaOverload.cpp	(revision 159968)
+++ b/tools/clang/lib/Sema/SemaOverload.cpp	(working copy)
@@ -9780,6 +9780,30 @@
     if (!Recovery.isInvalid())
       return Recovery;
 
+    // If there was only one candidate, and it wasn't viable due to substitution
+    // failure, produce its diagnostics instead of ours.
+    if (CandidateSet.begin() + 1 == CandidateSet.end() &&
+        CandidateSet.begin()->DeductionFailure.Result ==
+          Sema::TDK_SubstitutionFailure) {
+      OverloadCandidateSet::iterator Cand = CandidateSet.begin();
+      TemplateDeductionInfo Info(Context, CandidateSet.getLocation());
+      Info.setSFINAEContext(false);
+      FunctionDecl *Specialization = 0;
+      TemplateArgumentListInfo TemplateArgStorage, *ExplicitTemplateArgs = 0;
+      if (ULE->hasExplicitTemplateArgs()) {
+        ULE->getExplicitTemplateArgs().copyInto(TemplateArgStorage);
+        ExplicitTemplateArgs = &TemplateArgStorage;
+      }
+      TemplateDeductionResult Result =
+        DeduceTemplateArguments(Cand->Function->getDescribedFunctionTemplate(),
+                                ExplicitTemplateArgs,
+                                llvm::ArrayRef<Expr*>(Args, NumArgs),
+                                Specialization, Info);
+      assert(Result && "template deduction didn't fail on retry");
+      if (Result)
+        break;
+    }
+
     Diag(Fn->getLocStart(),
          diag::err_ovl_no_viable_function_in_call)
       << ULE->getName() << Fn->getSourceRange();
Index: lib/Sema/SemaTemplateInstantiate.cpp
===================================================================
--- a/tools/clang/lib/Sema/SemaTemplateInstantiate.cpp	(revision 159968)
+++ b/tools/clang/lib/Sema/SemaTemplateInstantiate.cpp	(working copy)
@@ -655,7 +655,8 @@
       // We're either substitution explicitly-specified template arguments
       // or deduced template arguments, so SFINAE applies.
       assert(Active->DeductionInfo && "Missing deduction info pointer");
-      return Active->DeductionInfo;
+      if (Active->DeductionInfo->isSFINAEContext())
+        return Active->DeductionInfo;
     }
   }