[clang-tidy] Do not trigger move fix for non-copy assignment operators in performance-unnecessary-value-param check

[malcolm.parsons]

LGTM.

clang-tools-extra/trunk/clang-tidy/utils/DeclRefExprUtils.cpp

 
 bool isCopyAssignmentArgument(const DeclRefExpr &DeclRef, const Decl &Decl,
                               ASTContext &Context) {
   auto UsedAsConstRefArg = forEachArgumentWithParam(
       declRefExpr(equalsNode(&DeclRef)),
       parmVarDecl(hasType(matchers::isReferenceToConst())));
   auto Matches = match(
       decl(hasDescendant(
-          cxxOperatorCallExpr(UsedAsConstRefArg, hasOverloadedOperatorName("="))
+          cxxOperatorCallExpr(UsedAsConstRefArg, hasOverloadedOperatorName("="),
+                              callee(cxxMethodDecl(isCopyAssignmentOperator())))
               .bind("operatorCallExpr"))),
       Decl, Context);
   return !Matches.empty();
 }
 
 } // namespace decl_ref_expr
 } // namespace utils
 } // namespace tidy
 } // namespace clang

clang-tools-extra/trunk/test/clang-tidy/performance-unnecessary-value-param.cpp

 
 void PositiveMoveOnCopyAssignment(ExpensiveMovableType E) {
   ExpensiveMovableType F;
   F = E;
   // CHECK-MESSAGES: [[@LINE-1]]:7: warning: parameter 'E' is passed by value
   // CHECK-FIXES: F = std::move(E);
 }
 
+struct NotCopyAssigned {
+  NotCopyAssigned &operator=(const ExpensiveMovableType &);
+};
+
+void PositiveNoMoveForNonCopyAssigmentOperator(ExpensiveMovableType E) {
+  // CHECK-MESSAGES: [[@LINE-1]]:69: warning: the parameter 'E' is copied
+  // CHECK-FIXES: void PositiveNoMoveForNonCopyAssigmentOperator(const ExpensiveMovableType& E) {
+  NotCopyAssigned N;
+  N = E;
+}
+
 // The argument could be moved but is not since copy statement is inside a loop.
 void PositiveNoMoveInsideLoop(ExpensiveMovableType E) {
   // CHECK-MESSAGES: [[@LINE-1]]:52: warning: the parameter 'E' is copied
   // CHECK-FIXES: void PositiveNoMoveInsideLoop(const ExpensiveMovableType& E) {
   for (;;) {
     auto F = E;
   }
 }