[clang-tidy] Ignore non-forwarded arguments if they are unused (#87832)

Author: SimplyDanny

clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp

@@ -9,8 +9,8 @@
 #include "MissingStdForwardCheck.h"
 #include "../utils/Matchers.h"
 #include "clang/AST/ASTContext.h"
-#include "clang/AST/ExprConcepts.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Basic/IdentifierTable.h"
 
 using namespace clang::ast_matchers;
 
@@ -79,6 +79,11 @@ AST_MATCHER_P(LambdaExpr, hasCaptureDefaultKind, LambdaCaptureDefault, Kind) {
   return Node.getCaptureDefault() == Kind;
 }
 
+AST_MATCHER(VarDecl, hasIdentifier) {
+  const IdentifierInfo *ID = Node.getIdentifier();
+  return ID != NULL && !ID->isPlaceholder();
+}
+
 } // namespace
 
 void MissingStdForwardCheck::registerMatchers(MatchFinder *Finder) {
@@ -125,12 +130,14 @@ void MissingStdForwardCheck::registerMatchers(MatchFinder *Finder) {
                    hasAncestor(expr(hasUnevaluatedContext())))));
 
   Finder->addMatcher(
-      parmVarDecl(parmVarDecl().bind("param"), isTemplateTypeParameter(),
-                  hasAncestor(functionDecl().bind("func")),
-                  hasAncestor(functionDecl(
-                      isDefinition(), equalsBoundNode("func"), ToParam,
-                      unless(anyOf(isDeleted(), hasDescendant(std::move(
-                                                    ForwardCallMatcher))))))),
+      parmVarDecl(
+          parmVarDecl().bind("param"), hasIdentifier(),
+          unless(hasAttr(attr::Kind::Unused)), isTemplateTypeParameter(),
+          hasAncestor(functionDecl().bind("func")),
+          hasAncestor(functionDecl(
+              isDefinition(), equalsBoundNode("func"), ToParam,
+              unless(anyOf(isDeleted(),
+                           hasDescendant(std::move(ForwardCallMatcher))))))),
       this);
 }
 

clang-tools-extra/docs/ReleaseNotes.rst

@@ -179,8 +179,9 @@ Changes in existing checks
 
 - Improved :doc:`cppcoreguidelines-missing-std-forward
   <clang-tidy/checks/cppcoreguidelines/missing-std-forward>` check by no longer
-  giving false positives for deleted functions and fix false negative when some
-  parameters are forwarded, but other aren't.
+  giving false positives for deleted functions, by fixing false negatives when only
+  a few parameters are forwarded and by ignoring parameters without a name (unused
+  arguments).
 
 - Improved :doc:`cppcoreguidelines-owning-memory
   <clang-tidy/checks/cppcoreguidelines/owning-memory>` check to properly handle

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp

@@ -198,3 +198,16 @@ struct S {
 };
 
 } // namespace deleted_functions
+
+namespace unused_arguments {
+
+template<typename F>
+void unused_argument1(F&&) {}
+
+template<typename F>
+void unused_argument2([[maybe_unused]] F&& f) {}
+
+template<typename F>
+void unused_argument3(F&& _) {}
+
+} // namespace unused_arguments