Improve error for assignment to incomplete class.

PR7681.

llvm-svn: 189510

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -2752,6 +2752,7 @@ def err_ovl_ambiguous_oper_unary : Error<
 def err_ovl_ambiguous_oper_binary : Error<
   "use of overloaded operator '%0' is ambiguous (with operand types %1 and %2)">;
 def err_ovl_no_viable_oper : Error<"no viable overloaded '%0'">;
+def note_assign_lhs_incomplete : Note<"type %0 is incomplete">;
 def err_ovl_deleted_oper : Error<
   "overload resolution selected %select{unavailable|deleted}0 operator '%1'%2">;
 def err_ovl_deleted_special_oper : Error<

clang/lib/Sema/SemaOverload.cpp

@@ -10714,6 +10714,11 @@ Sema::CreateOverloadedBinOp(SourceLocation OpLoc,
         Diag(OpLoc,  diag::err_ovl_no_viable_oper)
              << BinaryOperator::getOpcodeStr(Opc)
              << Args[0]->getSourceRange() << Args[1]->getSourceRange();
+        if (Args[0]->getType()->isIncompleteType()) {
+          Diag(OpLoc, diag::note_assign_lhs_incomplete)
+            << Args[0]->getType()
+            << Args[0]->getSourceRange() << Args[1]->getSourceRange();
+        }
       } else {
         // This is an erroneous use of an operator which can be overloaded by
         // a non-member function. Check for non-member operators which were

clang/test/SemaCXX/overloaded-operator.cpp

@@ -445,3 +445,10 @@ namespace test10 {
 struct InvalidOperatorEquals {
   InvalidOperatorEquals operator=() = delete; // expected-error {{overloaded 'operator=' must be a binary operator}}
 };
+
+namespace PR7681 {
+  template <typename PT1, typename PT2> class PointerUnion;
+  void foo(PointerUnion<int*, float*> &Result) {
+    Result = 1; // expected-error {{no viable overloaded '='}} // expected-note {{type 'PointerUnion<int *, float *>' is incomplete}}
+  }
+}