[clang-tidy] unnecessary-value-param: Allow moving of value arguments.

clang-tools-extra/clang-tidy/performance/UnnecessaryValueParamCheck.cpp

@@ -41,6 +41,17 @@ bool hasLoopStmtAncestor(const DeclRefExpr &DeclRef, const Decl &Decl,
   return Matches.empty();
 }
 
+bool isArgOfStdMove(const DeclRefExpr &DeclRef, const Decl &Decl,
+                    ASTContext &Context) {
+  return !match(traverse(TK_AsIs,
+                         decl(hasDescendant(callExpr(
+                             callee(functionDecl(hasName("std::move"))),
+                             hasArgument(0, ignoringParenImpCasts(declRefExpr(
+                                                equalsNode(&DeclRef)))))))),
+                Decl, Context)
+              .empty();
+}
+
 } // namespace
 
 UnnecessaryValueParamCheck::UnnecessaryValueParamCheck(
@@ -100,6 +111,11 @@ void UnnecessaryValueParamCheck::check(const MatchFinder::MatchResult &Result) {
       auto CanonicalType = Param->getType().getCanonicalType();
       const auto &DeclRefExpr = **AllDeclRefExprs.begin();
 
+      // The reference is in a call to `std::move`, do not warn.
+      if (isArgOfStdMove(DeclRefExpr, *Function, *Result.Context)) {
+        return;
+      }
+
       if (!hasLoopStmtAncestor(DeclRefExpr, *Function, *Result.Context) &&
           ((utils::type_traits::hasNonTrivialMoveConstructor(CanonicalType) &&
             utils::decl_ref_expr::isCopyConstructorArgument(

clang-tools-extra/docs/ReleaseNotes.rst

@@ -294,6 +294,7 @@ Changes in existing checks
   to avoid matching usage of functions within the current compilation unit.
   Added an option `IgnoreCoroutines` with the default value `true` to
   suppress this check for coroutines where passing by reference may be unsafe.
+  Fix false positive on by-value parameters that are only moved.
 
 - Improved :doc:`readability-convert-member-functions-to-static
   <clang-tidy/checks/readability/convert-member-functions-to-static>` check by

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

@@ -344,6 +344,10 @@ void ReferenceFunctionByCallingIt() {
   PositiveMessageAndFixAsFunctionIsCalled(ExpensiveToCopyType());
 }
 
+void NegativeMoved(ExpensiveToCopyType A) {
+  ExpensiveToCopyType Copy = std::move(A);
+}
+
 // Virtual method overrides of dependent types cannot be recognized unless they
 // are marked as override or final. Test that check is not triggered on methods
 // marked with override or final.