Allow a conversion from the empty initializer list {} to an

std::initializer_list<T> so long as <T> is known. This conversion has
identity rank.

llvm-svn: 154065

clang/lib/Sema/SemaOverload.cpp

@@ -4301,6 +4301,16 @@ TryListConversion(Sema &S, InitListExpr *From, QualType ToType,
               ImplicitConversionSequence::Worse)
         Result = ICS;
     }
+
+    // For an empty list, we won't have computed any conversion sequence.
+    // Introduce the identity conversion sequence.
+    if (From->getNumInits() == 0) {
+      Result.setStandard();
+      Result.Standard.setAsIdentityConversion();
+      Result.Standard.setFromType(ToType);
+      Result.Standard.setAllToTypes(ToType);
+    }
+
     Result.setListInitializationSequence();
     Result.setStdInitializerListElement(toStdInitializerList);
     return Result;

clang/test/SemaCXX/cxx0x-initializer-stdinitializerlist.cpp

@@ -166,3 +166,12 @@ namespace Decay {
     for( auto s : {"A", "BB", "CCC", "DDD"}) { }
   }
 }
+
+namespace PR12436 {
+  struct X {
+    template<typename T>
+    X(std::initializer_list<int>, T);
+  };
+  
+  X x({}, 17);
+}