Properly implement the part of C++ [over.match.funcs]p4 that treats

conversion functions as if their acting context were the class that
we're converting from (the implicit object argument's
type). Retroactively tweaking the implicit conversion sequence, as we
were trying to do before, breaks the invariants of that implicit
conversion sequence (e.g., the types and conversions don't match
up). Fixes <rdar://problem/8018274>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@111520 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Sema/SemaOverload.cpp b/lib/Sema/SemaOverload.cpp
index 2ee36f810193191b2703a3ff8fc6cb14842c1137..f8f04defb1b63e017f8fb635c5e924620ae46b4e 100644 (file)
--- a/lib/Sema/SemaOverload.cpp
+++ b/lib/Sema/SemaOverload.cpp
@@ -3741,26 +3741,46 @@ Sema::AddConversionCandidate(CXXConversionDecl *Conversion,
   Candidate.FinalConversion.setAsIdentityConversion();
   Candidate.FinalConversion.setFromType(ConvType);
   Candidate.FinalConversion.setAllToTypes(ToType);
-
-  // Determine the implicit conversion sequence for the implicit
-  // object parameter.
   Candidate.Viable = true;
   Candidate.Conversions.resize(1);
-  Candidate.Conversions[0]
-    = TryObjectArgumentInitialization(From->getType(), Conversion,
-                                      ActingContext);
-  
+
   // C++ [over.match.funcs]p4:
   //   For conversion functions, the function is considered to be a member of 
   //   the class of the implicit implied object argument for the purpose of 
   //   defining the type of the implicit object parameter.
-  if (Candidate.Conversions[0].Standard.Second == ICK_Derived_To_Base)
-    Candidate.Conversions[0].Standard.Second = ICK_Identity;
+  //
+  // Determine the implicit conversion sequence for the implicit
+  // object parameter.
+  QualType ImplicitParamType = From->getType();
+  if (const PointerType *FromPtrType = ImplicitParamType->getAs<PointerType>())
+    ImplicitParamType = FromPtrType->getPointeeType();
+  CXXRecordDecl *ConversionContext
+    = cast<CXXRecordDecl>(ImplicitParamType->getAs<RecordType>()->getDecl());
+  
+  Candidate.Conversions[0]
+    = TryObjectArgumentInitialization(From->getType(), Conversion,
+                                      ConversionContext);
+  
   if (Candidate.Conversions[0].isBad()) {
     Candidate.Viable = false;
     Candidate.FailureKind = ovl_fail_bad_conversion;
     return;
   }
+
+  // Make sure that the actual object argument initialization will work, when
+  // it comes down to it. This takes into account the actual acting context.
+  if (ConversionContext->getCanonicalDecl()
+                                        != ActingContext->getCanonicalDecl()) {
+    ImplicitConversionSequence ObjectConvertICS
+      = TryObjectArgumentInitialization(From->getType(), Conversion, 
+                                        ActingContext);
+    if (ObjectConvertICS.isBad()) {
+      Candidate.Viable = false;
+      Candidate.FailureKind = ovl_fail_bad_conversion;
+      Candidate.Conversions[0] = ObjectConvertICS;
+      return;
+    }
+  }
   
   // We won't go through a user-define type conversion function to convert a 
   // derived to base as such conversions are given Conversion Rank. They only

diff --git a/test/SemaCXX/conversion-function.cpp b/test/SemaCXX/conversion-function.cpp
index 951cdb3f51ac93050980023ccc9990a7ba8c3181..3d544ae03cfe2f5c0cdf3ff466cbcb4c997f66f0 100644 (file)
--- a/test/SemaCXX/conversion-function.cpp
+++ b/test/SemaCXX/conversion-function.cpp
@@ -270,3 +270,40 @@ namespace PR7934 {
     fake_memcpy(ptr);
   }
 }
+
+namespace rdar8018274 {
+  struct X { };
+  struct Y {
+    operator const struct X *() const;
+  };
+
+  struct Z : Y {
+    operator struct X * ();
+  };
+
+  void test() {
+    Z x;
+    (void) (x != __null);
+  }
+
+
+  struct Base {
+    operator int();
+  };
+
+  struct Derived1 : Base { };
+
+  struct Derived2 : Base { };
+
+  struct SuperDerived : Derived1, Derived2 { 
+    using Derived1::operator int;
+  };
+
+  struct UeberDerived : SuperDerived {
+    operator long();
+  };
+
+  void test2(UeberDerived ud) {
+    int i = ud; // expected-error{{ambiguous conversion from derived class 'rdar8018274::SuperDerived' to base class 'rdar8018274::Base'}}
+  }
+}