[clang-tools-extra] [clang-tidy] New checker: modernize-use-va-opt to replace the `, ##__VAR_ARG__` GNU extension (PR #188474)
via cfe-commits
cfe-commits at lists.llvm.org
Wed Mar 25 05:47:49 PDT 2026
https://github.com/serge-sans-paille updated https://github.com/llvm/llvm-project/pull/188474
>From 30e9d5ccb280d2f8737dba77ecb9574631277abf Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton at mozilla.com>
Date: Wed, 25 Mar 2026 13:25:01 +0100
Subject: [PATCH 1/4] [clang-tidy] New checker: modernize-use-va-opt to replace
the `, ##__VAR_ARG__` GNU extension
---
.../clang-tidy/modernize/CMakeLists.txt | 1 +
.../modernize/ModernizeTidyModule.cpp | 2 +
.../clang-tidy/modernize/UseVaOptCheck.cpp | 71 +++++++++++++++++++
.../clang-tidy/modernize/UseVaOptCheck.h | 33 +++++++++
clang-tools-extra/docs/ReleaseNotes.rst | 5 ++
.../docs/clang-tidy/checks/list.rst | 1 +
.../checks/modernize/use-va-opt.rst | 19 +++++
.../checkers/modernize/use-va-opt.cpp | 37 ++++++++++
8 files changed, 169 insertions(+)
create mode 100644 clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
create mode 100644 clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.h
create mode 100644 clang-tools-extra/docs/clang-tidy/checks/modernize/use-va-opt.rst
create mode 100644 clang-tools-extra/test/clang-tidy/checkers/modernize/use-va-opt.cpp
diff --git a/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt b/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt
index 2c5c44db587fe..71aebcaf1feca 100644
--- a/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt
@@ -57,6 +57,7 @@ add_clang_library(clangTidyModernizeModule STATIC
UseTransparentFunctorsCheck.cpp
UseUncaughtExceptionsCheck.cpp
UseUsingCheck.cpp
+ UseVaOptCheck.cpp
LINK_LIBS
clangTidy
diff --git a/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp b/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp
index cc13da7535bcb..e45538213c6e7 100644
--- a/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp
@@ -57,6 +57,7 @@
#include "UseTransparentFunctorsCheck.h"
#include "UseUncaughtExceptionsCheck.h"
#include "UseUsingCheck.h"
+#include "UseVaOptCheck.h"
using namespace clang::ast_matchers;
@@ -145,6 +146,7 @@ class ModernizeModule : public ClangTidyModule {
CheckFactories.registerCheck<UseUncaughtExceptionsCheck>(
"modernize-use-uncaught-exceptions");
CheckFactories.registerCheck<UseUsingCheck>("modernize-use-using");
+ CheckFactories.registerCheck<UseVaOptCheck>("modernize-use-va-opt");
}
};
diff --git a/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
new file mode 100644
index 0000000000000..2ea4acf20f740
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
@@ -0,0 +1,71 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "UseVaOptCheck.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Lex/PPCallbacks.h"
+#include "clang/Lex/Preprocessor.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::modernize {
+
+namespace {
+class VaOptPPCallbacks : public PPCallbacks {
+public:
+ VaOptPPCallbacks(Preprocessor *PP, UseVaOptCheck *Check)
+ : PP(PP), Check(Check) {}
+
+ void MacroDefined(const Token &MacroNameTok,
+ const MacroDirective *MD) override {
+ const MacroInfo *MI = MD->getMacroInfo();
+ if (!MI->isVariadic())
+ return;
+
+ std::optional<Token> PrevComma;
+ bool PrevHashHash = false;
+ ;
+ for (Token Tok : MI->tokens()) {
+ if (PrevHashHash) {
+ if (const auto *II = Tok.getIdentifierInfo();
+ II && II->getName() == "__VA_ARGS__") {
+ // FIXME: The replacement really should be " __VA_OPT__(,)
+ // __VA_ARGS__", but this breaks the fixit which removes the , in that
+ // case o_O.
+ Check->diag(Tok.getLocation(),
+ "Use __VA_OPT__ instead of GNU extension to __VA_ARGS__")
+ << FixItHint::CreateReplacement(
+ SourceRange(PrevComma->getLocation(), Tok.getLocation()),
+ " __VA_OPT__(',') __VA_ARGS__");
+ }
+ PrevComma = std::nullopt;
+ PrevHashHash = false;
+ } else if (PrevComma) {
+ if (Tok.is(tok::hashhash))
+ PrevHashHash = true;
+ else
+ PrevComma = std::nullopt;
+ } else if (Tok.is(tok::comma)) {
+ PrevComma = Tok;
+ }
+ }
+ }
+
+private:
+ Preprocessor *PP;
+ UseVaOptCheck *Check;
+};
+} // namespace
+
+void UseVaOptCheck::registerPPCallbacks(const SourceManager &SM,
+ Preprocessor *PP,
+ Preprocessor *ModuleExpanderPP) {
+ PP->addPPCallbacks(std::make_unique<VaOptPPCallbacks>(PP, this));
+}
+
+} // namespace clang::tidy::modernize
diff --git a/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.h b/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.h
new file mode 100644
index 0000000000000..11493f298d842
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.h
@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USEVAOPTCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USEVAOPTCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::modernize {
+
+/// Use __VA_OPT__ instead of ##__VA_ARGS__ GNU extension.
+///
+/// For the user-facing documentation see:
+/// https://clang.llvm.org/extra/clang-tidy/checks/modernize/use-va-opt.html
+class UseVaOptCheck : public ClangTidyCheck {
+public:
+ UseVaOptCheck(StringRef Name, ClangTidyContext *Context)
+ : ClangTidyCheck(Name, Context) {}
+ void registerPPCallbacks(const SourceManager &SM, Preprocessor *PP,
+ Preprocessor *ModuleExpanderPP) override;
+ bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+ return LangOpts.CPlusPlus20 || LangOpts.C23;
+ }
+};
+
+} // namespace clang::tidy::modernize
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USEVAOPTCHECK_H
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 49901f8a706c6..c646d5281c0b5 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -145,6 +145,11 @@ New checks
Finds places where structured bindings could be used to decompose pairs and
suggests replacing them.
+- New :doc:`modernize-use-va-opt
+ <clang-tidy/checks/modernize/use-va-opt>` check.
+
+ Use __VA_OPT__ instead of ##__VA_ARGS__ GNU extension.
+
- New :doc:`performance-string-view-conversions
<clang-tidy/checks/performance/string-view-conversions>` check.
diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index ceab1e9414951..2441f9e63fcff 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -336,6 +336,7 @@ Clang-Tidy Checks
:doc:`modernize-use-transparent-functors <modernize/use-transparent-functors>`, "Yes"
:doc:`modernize-use-uncaught-exceptions <modernize/use-uncaught-exceptions>`, "Yes"
:doc:`modernize-use-using <modernize/use-using>`, "Yes"
+ :doc:`modernize-use-va-opt <modernize/use-va-opt>`, "Yes"
:doc:`mpi-buffer-deref <mpi/buffer-deref>`, "Yes"
:doc:`mpi-type-mismatch <mpi/type-mismatch>`, "Yes"
:doc:`objc-assert-equals <objc/assert-equals>`, "Yes"
diff --git a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-va-opt.rst b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-va-opt.rst
new file mode 100644
index 0000000000000..af631ff18419a
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-va-opt.rst
@@ -0,0 +1,19 @@
+.. title:: clang-tidy - modernize-use-va-opt
+
+modernize-use-va-opt
+====================
+
+Suggest using ``__VA_OPT__(,)`` instead of ``, ##__VA_ARGS__`` when implementing
+variadic macro. ``, ##__VA_ARGS__`` is a GNU extension.
+
+.. code:: c++
+
+ extern int bar(...);
+ #define FOO(a, ...) bar(a, ##__VA_ARGS__)
+
+becomes:
+
+.. code:: c++
+
+ extern int bar(...);
+ #define FOO(a, ...) bar(a __VA_OPT__(,) __VA_ARGS__)
diff --git a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-va-opt.cpp b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-va-opt.cpp
new file mode 100644
index 0000000000000..b0fde0000de23
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-va-opt.cpp
@@ -0,0 +1,37 @@
+// RUN: %check_clang_tidy -std=c++20-or-later %s modernize-use-va-opt %t
+
+extern void foo(...);
+
+
+// CHECK-MESSAGES: :[[@LINE+2]]:26: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
+// CHECK-FIXES: #define M0(...) foo(1 __VA_OPT__(',') __VA_ARGS__)
+#define M0(...) foo(1, ##__VA_ARGS__)
+
+// CHECK-MESSAGES: :[[@LINE+2]]:27: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
+// CHECK-FIXES: #define M1(...) foo(1 __VA_OPT__(',') __VA_ARGS__)
+#define M1(...) foo(1, ## __VA_ARGS__)
+
+// CHECK-MESSAGES: :[[@LINE+2]]:27: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
+// CHECK-FIXES: #define M2(...) foo(1 __VA_OPT__(',') __VA_ARGS__)
+#define M2(...) foo(1 ,## __VA_ARGS__)
+
+// CHECK-MESSAGES: :[[@LINE+2]]:28: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
+// CHECK-FIXES: #define M3(...) foo(1 __VA_OPT__(',') __VA_ARGS__)
+#define M3(...) foo(1 , ## __VA_ARGS__)
+
+// CHECK-MESSAGES: :[[@LINE+3]]:28: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
+// CHECK-MESSAGES: :[[@LINE+2]]:44: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
+// CHECK-FIXES: #define M4(...) foo(1 __VA_OPT__(',') __VA_ARGS__ __VA_OPT__(',') __VA_ARGS__)
+#define M4(...) foo(1 , ## __VA_ARGS__, ## __VA_ARGS__)
+
+// No message, this will never add a comma before __VA_ARGS__
+#define P0(...) foo(1 ##__VA_ARGS__)
+
+// No message, this will never add a comma before __VA_ARGS__
+#define P1(...) foo(__VA_ARGS__)
+
+// No message, this will never add a comma before __VA_ARGS__
+#define P2(...) foo(##__VA_ARGS__)
+
+// No message, this will never add a comma before __VA_ARGS__
+#define P3(...) foo(, __VA_ARGS__)
>From eba0f40290441d23a0799502331e2a3d1305e229 Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton at mozilla.com>
Date: Wed, 25 Mar 2026 13:42:35 +0100
Subject: [PATCH 2/4] fixup! [clang-tidy] New checker: modernize-use-va-opt to
replace the `, ##__VAR_ARG__` GNU extension
---
clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
index 2ea4acf20f740..921038aa15afa 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
@@ -29,9 +29,9 @@ class VaOptPPCallbacks : public PPCallbacks {
std::optional<Token> PrevComma;
bool PrevHashHash = false;
- ;
- for (Token Tok : MI->tokens()) {
+ for (const Token Tok : MI->tokens()) {
if (PrevHashHash) {
+ assert(PrevComma);
if (const auto *II = Tok.getIdentifierInfo();
II && II->getName() == "__VA_ARGS__") {
// FIXME: The replacement really should be " __VA_OPT__(,)
@@ -46,11 +46,13 @@ class VaOptPPCallbacks : public PPCallbacks {
PrevComma = std::nullopt;
PrevHashHash = false;
} else if (PrevComma) {
+ assert(!PrevHashHash);
if (Tok.is(tok::hashhash))
PrevHashHash = true;
else
PrevComma = std::nullopt;
} else if (Tok.is(tok::comma)) {
+ assert(!PrevHashHash);
PrevComma = Tok;
}
}
>From d1c61e30969afa28be9cb46b21e465fddc453dde Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton at mozilla.com>
Date: Wed, 25 Mar 2026 13:44:13 +0100
Subject: [PATCH 3/4] fixup! fixup! [clang-tidy] New checker:
modernize-use-va-opt to replace the `, ##__VAR_ARG__` GNU extension
---
.../clang-tidy/modernize/UseVaOptCheck.cpp | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
index 921038aa15afa..8c01d7d9985f2 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
@@ -18,8 +18,7 @@ namespace clang::tidy::modernize {
namespace {
class VaOptPPCallbacks : public PPCallbacks {
public:
- VaOptPPCallbacks(Preprocessor *PP, UseVaOptCheck *Check)
- : PP(PP), Check(Check) {}
+ VaOptPPCallbacks(UseVaOptCheck &Check) : Check(Check) {}
void MacroDefined(const Token &MacroNameTok,
const MacroDirective *MD) override {
@@ -37,8 +36,8 @@ class VaOptPPCallbacks : public PPCallbacks {
// FIXME: The replacement really should be " __VA_OPT__(,)
// __VA_ARGS__", but this breaks the fixit which removes the , in that
// case o_O.
- Check->diag(Tok.getLocation(),
- "Use __VA_OPT__ instead of GNU extension to __VA_ARGS__")
+ Check.diag(Tok.getLocation(),
+ "Use __VA_OPT__ instead of GNU extension to __VA_ARGS__")
<< FixItHint::CreateReplacement(
SourceRange(PrevComma->getLocation(), Tok.getLocation()),
" __VA_OPT__(',') __VA_ARGS__");
@@ -59,15 +58,14 @@ class VaOptPPCallbacks : public PPCallbacks {
}
private:
- Preprocessor *PP;
- UseVaOptCheck *Check;
+ UseVaOptCheck &Check;
};
} // namespace
void UseVaOptCheck::registerPPCallbacks(const SourceManager &SM,
Preprocessor *PP,
Preprocessor *ModuleExpanderPP) {
- PP->addPPCallbacks(std::make_unique<VaOptPPCallbacks>(PP, this));
+ PP->addPPCallbacks(std::make_unique<VaOptPPCallbacks>(*this));
}
} // namespace clang::tidy::modernize
>From 41e26d5b9c28c7575aa2f1ae8694af2849df45b5 Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton at mozilla.com>
Date: Wed, 25 Mar 2026 13:47:28 +0100
Subject: [PATCH 4/4] fixup! fixup! fixup! [clang-tidy] New checker:
modernize-use-va-opt to replace the `, ##__VAR_ARG__` GNU extension
---
.../clang-tidy/modernize/UseVaOptCheck.cpp | 5 +----
.../test/clang-tidy/checkers/modernize/use-va-opt.cpp | 10 +++++-----
2 files changed, 6 insertions(+), 9 deletions(-)
diff --git a/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
index 8c01d7d9985f2..8fde502bc5872 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseVaOptCheck.cpp
@@ -33,14 +33,11 @@ class VaOptPPCallbacks : public PPCallbacks {
assert(PrevComma);
if (const auto *II = Tok.getIdentifierInfo();
II && II->getName() == "__VA_ARGS__") {
- // FIXME: The replacement really should be " __VA_OPT__(,)
- // __VA_ARGS__", but this breaks the fixit which removes the , in that
- // case o_O.
Check.diag(Tok.getLocation(),
"Use __VA_OPT__ instead of GNU extension to __VA_ARGS__")
<< FixItHint::CreateReplacement(
SourceRange(PrevComma->getLocation(), Tok.getLocation()),
- " __VA_OPT__(',') __VA_ARGS__");
+ " __VA_OPT__(,) __VA_ARGS__");
}
PrevComma = std::nullopt;
PrevHashHash = false;
diff --git a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-va-opt.cpp b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-va-opt.cpp
index b0fde0000de23..c405b076809ca 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-va-opt.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-va-opt.cpp
@@ -4,24 +4,24 @@ extern void foo(...);
// CHECK-MESSAGES: :[[@LINE+2]]:26: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
-// CHECK-FIXES: #define M0(...) foo(1 __VA_OPT__(',') __VA_ARGS__)
+// CHECK-FIXES: #define M0(...) foo(1 __VA_OPT__(,) __VA_ARGS__)
#define M0(...) foo(1, ##__VA_ARGS__)
// CHECK-MESSAGES: :[[@LINE+2]]:27: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
-// CHECK-FIXES: #define M1(...) foo(1 __VA_OPT__(',') __VA_ARGS__)
+// CHECK-FIXES: #define M1(...) foo(1 __VA_OPT__(,) __VA_ARGS__)
#define M1(...) foo(1, ## __VA_ARGS__)
// CHECK-MESSAGES: :[[@LINE+2]]:27: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
-// CHECK-FIXES: #define M2(...) foo(1 __VA_OPT__(',') __VA_ARGS__)
+// CHECK-FIXES: #define M2(...) foo(1 __VA_OPT__(,) __VA_ARGS__)
#define M2(...) foo(1 ,## __VA_ARGS__)
// CHECK-MESSAGES: :[[@LINE+2]]:28: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
-// CHECK-FIXES: #define M3(...) foo(1 __VA_OPT__(',') __VA_ARGS__)
+// CHECK-FIXES: #define M3(...) foo(1 __VA_OPT__(,) __VA_ARGS__)
#define M3(...) foo(1 , ## __VA_ARGS__)
// CHECK-MESSAGES: :[[@LINE+3]]:28: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
// CHECK-MESSAGES: :[[@LINE+2]]:44: warning: Use __VA_OPT__ instead of GNU extension to __VA_ARGS__ [modernize-use-va-opt]
-// CHECK-FIXES: #define M4(...) foo(1 __VA_OPT__(',') __VA_ARGS__ __VA_OPT__(',') __VA_ARGS__)
+// CHECK-FIXES: #define M4(...) foo(1 __VA_OPT__(,) __VA_ARGS__ __VA_OPT__(,) __VA_ARGS__)
#define M4(...) foo(1 , ## __VA_ARGS__, ## __VA_ARGS__)
// No message, this will never add a comma before __VA_ARGS__
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