[clang-tidy] Add flag to specify an alternative to std::forward #138755

DimitrijeDobrota · 2025-05-06T20:31:49Z

Since std::forward is nothing more than a cast, part of STL and not the language itself, it's easy to provide a custom implementation if one wishes not to include the entirety of .

Added flag (ForwardFunction) provides a way to continue using this essential check even with the custom implementation of forwarding.

Since :: are specified before std::forward, I am not entirely sure whether it would be required for the custom function. In my testing it worked both with and without ::.

github-actions · 2025-05-06T20:32:12Z

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llvmbot · 2025-05-06T20:32:43Z

@llvm/pr-subscribers-clang-tidy

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

Author: Dimitrije Dobrota (DimitrijeDobrota)

Changes

Since std::forward is nothing more than a cast, part of STL and not the language itself, it's easy to provide a custom implementation if one wishes not to include the entirety of <utility>.

Added flag (ForwardFunction) provides a way to continue using this essential check even with the custom implementation of forwarding.

Since :: are specified before std::forward, I am not entirely sure whether it would be required for the custom function. In my testing it worked both with and without ::.

Full diff: https://github.com/llvm/llvm-project/pull/138755.diff

4 Files Affected:

(modified) clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp (+10-1)
(modified) clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.h (+5-2)
(modified) clang-tools-extra/docs/ReleaseNotes.rst (+4)
(modified) clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst (+8)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
index bbb35228ce47f..c90966413de69 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
@@ -124,7 +124,7 @@ void MissingStdForwardCheck::registerMatchers(MatchFinder *Finder) {
                           equalsBoundNode("param"), equalsBoundNode("var")))))),
                 CapturedInLambda)),
       callee(unresolvedLookupExpr(hasAnyDeclaration(
-          namedDecl(hasUnderlyingDecl(hasName("::std::forward")))))),
+          namedDecl(hasUnderlyingDecl(hasName(ForwardFunction)))))),
 
       unless(anyOf(hasAncestor(typeLoc()),
                    hasAncestor(expr(hasUnevaluatedContext())))));
@@ -153,4 +153,13 @@ void MissingStdForwardCheck::check(const MatchFinder::MatchResult &Result) {
       << Param;
 }
 
+MissingStdForwardCheck::MissingStdForwardCheck(StringRef Name,
+                                               ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      ForwardFunction(Options.get("ForwardFunction", "::std::forward")) {}
+
+void MissingStdForwardCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "ForwardFunction", ForwardFunction);
+}
+
 } // namespace clang::tidy::cppcoreguidelines
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.h b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.h
index 5995ad588855e..f833b8031f8af 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.h
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.h
@@ -21,8 +21,7 @@ namespace clang::tidy::cppcoreguidelines {
 /// http://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines/missing-std-forward.html
 class MissingStdForwardCheck : public ClangTidyCheck {
 public:
-  MissingStdForwardCheck(StringRef Name, ClangTidyContext *Context)
-      : ClangTidyCheck(Name, Context) {}
+  MissingStdForwardCheck(StringRef Name, ClangTidyContext *Context);
   void registerMatchers(ast_matchers::MatchFinder *Finder) override;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
   bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
@@ -31,6 +30,10 @@ class MissingStdForwardCheck : public ClangTidyCheck {
   std::optional<TraversalKind> getCheckTraversalKind() const override {
     return TK_IgnoreUnlessSpelledInSource;
   }
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+
+private:
+  const StringRef ForwardFunction;
 };
 
 } // namespace clang::tidy::cppcoreguidelines
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 579fca54924d5..9c71d651af75f 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -219,6 +219,10 @@ Changes in existing checks
   tolerating fix-it breaking compilation when functions is used as pointers
   to avoid matching usage of functions within the current compilation unit.
 
+- Improved :doc:`cppcoreguidelines-missing-std-forward
+  <clang-tidy/checks/cppcoreguidelines/missing-std-forward>` check by adding a
+  flag to specify the function used for forwarding instead of ``std::forward``.
+
 Removed checks
 ^^^^^^^^^^^^^^
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst
index 0c311b59a5d5a..d6cc1e53f768d 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst
@@ -35,6 +35,14 @@ Example:
     f(1, 2); // Incorrect - may not invoke the desired qualified function operator
   }
 
+Options
+-------
+
+.. option:: ForwardFunction
+
+   Specify the function used for forwarding.
+   Default is `::std::forward`.
+
 This check implements `F.19
 <http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rf-forward>`_
 from the C++ Core Guidelines.

EugeneZelenko · 2025-05-07T13:57:42Z

clang-tools-extra/docs/ReleaseNotes.rst

@@ -219,6 +219,10 @@ Changes in existing checks
  tolerating fix-it breaking compilation when functions is used as pointers
  to avoid matching usage of functions within the current compilation unit.

+- Improved :doc:`cppcoreguidelines-missing-std-forward


Please keep alphabetical order (by check name) in this list.

HerrCai0907

LGTM.
It looks similar as #138757. could you add a test for both PR.

DimitrijeDobrota · 2025-05-08T15:27:02Z

LGTM. It looks similar as #138757. could you add a test for both PR.

I have the issue where I want to test the custom_move and I need check to pass only for -check-suffix=,MOVEFUNCTION and fail for everything else, since it still expects ::std::move. I am not sure how to write this. Apart from this, I've managed to add necessary checks for the existing set of test cases.

void move_with_custom(Obj&& o) {
  // CHECK-MESSAGES: :[[@LINE-1]]:29: warning: rvalue reference parameter 'o' is never moved from inside the function body [cppcoreguidelines-rvalue-reference-param-not-moved]
  // CHECK-MESSAGES-MOVEFUNCTION: no error in this case

  Obj other{custom_move(o)};

vbvictor · 2025-06-29T20:32:19Z

I have the issue where I want to test the custom_move and I need check to pass only for -check-suffix=,MOVEFUNCTION and fail for everything else, since it still expects ::std::move. I am not sure how to write this.

You can create a separate file missing-std-forward-custom-function.cpp, where you would have your custom defined function. The same should be done for other check.

After added tests and rebase on fresh main, we can land this.

Since std::forward is nothing more than a cast, part of STL and not the language itself, it's easy to provide a custom implementation if one wishes not to include the entirety of <utility>. Added flag (ForwardFunction) provides a way to continue using this essential check even with the custom implementation of forwarding.

clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst

…sing-std-forward.rst Co-authored-by: EugeneZelenko <[email protected]>

vbvictor

LGTM, can merge it after CI pass

github-actions · 2025-06-30T19:13:50Z

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…#138755) Since std::forward is nothing more than a cast, part of STL and not the language itself, it's easy to provide a custom implementation if one wishes not to include the entirety of <utility>. Added flag (ForwardFunction) provides a way to continue using this essential check even with the custom implementation of forwarding. --------- Co-authored-by: EugeneZelenko <[email protected]>

llvmbot added clang-tools-extra clang-tidy labels May 6, 2025

EugeneZelenko requested review from PiotrZSL, carlosgalvezp and HerrCai0907 May 7, 2025 13:56

EugeneZelenko reviewed May 7, 2025

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HerrCai0907 approved these changes May 8, 2025

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DimitrijeDobrota changed the title ~~Add flag to specify an alternative to std::forward~~ [clang-tidy] Add flag to specify an alternative to std::forward May 8, 2025

5chmidti self-requested a review June 21, 2025 11:51

DimitrijeDobrota added 3 commits June 29, 2025 23:58

Fix alphabetical order in ReleaseNotes

af8f4e5

Add test

65fd4ab

DimitrijeDobrota force-pushed the cppcoreguidelines-missing-std-forward branch from f34bbfa to 65fd4ab Compare June 30, 2025 17:15

EugeneZelenko reviewed Jun 30, 2025

View reviewed changes

clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst Outdated Show resolved Hide resolved

Update clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/mis…

62bbfbb

…sing-std-forward.rst Co-authored-by: EugeneZelenko <[email protected]>

vbvictor approved these changes Jun 30, 2025

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vbvictor merged commit 6a57af8 into llvm:main Jun 30, 2025
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