PR17295: Do not allow explicit conversion functions to be used in cases where

an additional conversion (other than a qualification conversion) would be
required after the explicit conversion.

Conversely, do allow explicit conversion functions to be used when initializing
a temporary for a reference binding in direct-list-initialization.

llvm-svn: 191150

1 files changed, 11 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 800f9832498..df18752bfa8 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -5829,6 +5829,17 @@ Sema::AddConversionCandidate(CXXConversionDecl *Conversion,
     ConvType = Conversion->getConversionType().getNonReferenceType();
   }
 
+  // Per C++ [over.match.conv]p1, [over.match.ref]p1, an explicit conversion
+  // operator is only a candidate if its return type is the target type or
+  // can be converted to the target type with a qualification conversion.
+  bool ObjCLifetimeConversion;
+  QualType ToNonRefType = ToType.getNonReferenceType();
+  if (Conversion->isExplicit() &&
+      !Context.hasSameUnqualifiedType(ConvType, ToNonRefType) &&
+      !IsQualificationConversion(ConvType, ToNonRefType, /*CStyle*/false,
+                                 ObjCLifetimeConversion))
+    return;
+
   // Overload resolution is always an unevaluated context.
   EnterExpressionEvaluationContext Unevaluated(*this, Sema::Unevaluated);