[clang-tidy] Ignore non-forwarded arguments if they are unnamed

[SimplyDanny]

Fixes #87697.

[llvmbot]

@llvm/pr-subscribers-clang-tools-extra

@llvm/pr-subscribers-clang-tidy

Author: Danny Mösch (SimplyDanny)

Changes

Fixes #87697.

---

Full diff: https://github.com/llvm/llvm-project/pull/87832.diff

3 Files Affected:

• (modified) clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp (+9-6)
• (modified) clang-tools-extra/docs/ReleaseNotes.rst (+4)
• (modified) clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp (+3)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
index 87fd8adf997082..6817bcb24c8112 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
@@ -79,6 +79,8 @@ AST_MATCHER_P(LambdaExpr, hasCaptureDefaultKind, LambdaCaptureDefault, Kind) {
   return Node.getCaptureDefault() == Kind;
 }
 
+AST_MATCHER(ParmVarDecl, hasAnyName) { return !Node.getName().empty(); }
+
 } // namespace
 
 void MissingStdForwardCheck::registerMatchers(MatchFinder *Finder) {
@@ -125,12 +127,13 @@ 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"), hasAnyName(), isTemplateTypeParameter(),
+          hasAncestor(functionDecl().bind("func")),
+          hasAncestor(functionDecl(
+              isDefinition(), equalsBoundNode("func"), ToParam,
+              unless(anyOf(isDeleted(),
+                           hasDescendant(std::move(ForwardCallMatcher))))))),
       this);
 }
 
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 456e09204fa2f9..f79d3b9f362063 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -182,6 +182,10 @@ Changes in existing checks
   giving false positives for deleted functions and fix false negative when some
   parameters are forwarded, but other aren't.
 
+- Improved :doc:`cppcoreguidelines-missing-std-forward
+  <clang-tidy/checks/cppcoreguidelines/missing-std-forward>` check by ignoring
+  parameters without a name (unused arguments).
+
 - Improved :doc:`cppcoreguidelines-owning-memory
   <clang-tidy/checks/cppcoreguidelines/owning-memory>` check to properly handle
   return type in lambdas and in nested functions.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp
index 9a50eabf619bd5..c435a0e023ba0b 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp
@@ -198,3 +198,6 @@ struct S {
 };
 
 } // namespace deleted_functions
+
+template<typename F>
+void unused_argument(F&&) {}

[PiotrZSL]

Current code is fine, wound be good ignore also unused.

[PiotrZSL]

You should also ignore unused variables, like [[maybe_unused]] with:

unless(hasAttr(attr::Kind::Unused)),

And you could also use:

unless(isReferenced()),

with:

AST_MATCHER(VarDecl, isReferenced) { return Node.isReferenced(); }

[SimplyDanny]

I went with unless(hasAttr(attr::Kind::Unused)) and hasIdentifier. isReferenced() doesn't play nicely with constructor initializer lists. It seems that it doesn't consider a declaration used when it's only used to initialize a field.