[Sema] Improve diagnostics for const- and ref-qualified member functions

Summary:
Adjust wording for const-qualification mismatch to be a little more clear.

Also add another diagnostic for a ref qualifier mismatch, which previously produced a useless error (this error path is simply very old; see rL119336):

Before:
  error: cannot initialize object parameter of type 'X0' with an expression of type 'X0'

After:
  error: 'this' argument to member function 'rvalue' is an lvalue, but function has rvalue ref-qualifier

Reviewers: rsmith, aaron.ballman

Reviewed By: aaron.ballman

Subscribers: lebedev.ri, aaron.ballman, cfe-commits

Differential Revision: https://reviews.llvm.org/D39937

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@321592 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 2 deletions

diff --git a/lib/Sema/SemaOverload.cpp b/lib/Sema/SemaOverload.cpp
index 2144845f4d..07d931552f 100644
--- a/lib/Sema/SemaOverload.cpp
+++ b/lib/Sema/SemaOverload.cpp
@@ -5145,7 +5145,8 @@ Sema::PerformObjectArgumentInitialization(Expr *From,
       *this, From->getLocStart(), From->getType(), FromClassification, Method,
       Method->getParent());
   if (ICS.isBad()) {
-    if (ICS.Bad.Kind == BadConversionSequence::bad_qualifiers) {
+    switch (ICS.Bad.Kind) {
+    case BadConversionSequence::bad_qualifiers: {
       Qualifiers FromQs = FromRecordType.getQualifiers();
       Qualifiers ToQs = DestType.getQualifiers();
       unsigned CVR = FromQs.getCVRQualifiers() & ~ToQs.getCVRQualifiers();
@@ -5158,10 +5159,28 @@ Sema::PerformObjectArgumentInitialization(Expr *From,
           << Method->getDeclName();
         return ExprError();
       }
+      break;
+    }
+
+    case BadConversionSequence::lvalue_ref_to_rvalue:
+    case BadConversionSequence::rvalue_ref_to_lvalue: {
+      bool IsRValueQualified =
+        Method->getRefQualifier() == RefQualifierKind::RQ_RValue;
+      Diag(From->getLocStart(), diag::err_member_function_call_bad_ref)
+        << Method->getDeclName() << FromClassification.isRValue()
+        << IsRValueQualified;
+      Diag(Method->getLocation(), diag::note_previous_decl)
+        << Method->getDeclName();
+      return ExprError();
+    }
+
+    case BadConversionSequence::no_conversion:
+    case BadConversionSequence::unrelated_class:
+      break;
     }
 
     return Diag(From->getLocStart(),
-                diag::err_implicit_object_parameter_init)
+                diag::err_member_function_call_bad_type)
        << ImplicitParamRecordType << FromRecordType << From->getSourceRange();
   }