[clang-tools-extra] [clang-tidy] Add cerrno check to bugprone (PR #213015)
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Thu Jul 30 05:49:02 PDT 2026
llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang-tools-extra
Author: Csaba Zeitvogel (zeitcsabi)
<details>
<summary>Changes</summary>
This simple check is based on the cerrno portion of MSC38-C.
---
Full diff: https://github.com/llvm/llvm-project/pull/213015.diff
8 Files Affected:
- (modified) clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp (+3)
- (modified) clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt (+1)
- (added) clang-tools-extra/clang-tidy/bugprone/CerrnoCheck.cpp (+38)
- (added) clang-tools-extra/clang-tidy/bugprone/CerrnoCheck.h (+35)
- (modified) clang-tools-extra/docs/ReleaseNotes.rst (+5)
- (added) clang-tools-extra/docs/clang-tidy/checks/bugprone/cerrno.rst (+17)
- (modified) clang-tools-extra/docs/clang-tidy/checks/list.rst (+1)
- (added) clang-tools-extra/test/clang-tidy/checkers/bugprone/cerrno.cpp (+25)
``````````diff
diff --git a/clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp b/clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp
index 3aa39d10ceb5d..54f0e7345ff97 100644
--- a/clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp
@@ -18,6 +18,7 @@
#include "BranchCloneCheck.h"
#include "CapturingThisInMemberVariableCheck.h"
#include "CastingThroughVoidCheck.h"
+#include "CerrnoCheck.h"
#include "ChainedComparisonCheck.h"
#include "CommandProcessorCheck.h"
#include "ComparePointerToMemberVirtualFunctionCheck.h"
@@ -144,6 +145,8 @@ class BugproneModule : public ClangTidyModule {
"bugprone-capturing-this-in-member-variable");
CheckFactories.registerCheck<CastingThroughVoidCheck>(
"bugprone-casting-through-void");
+ CheckFactories.registerCheck<CerrnoCheck>(
+ "bugprone-cerrno");
CheckFactories.registerCheck<ChainedComparisonCheck>(
"bugprone-chained-comparison");
CheckFactories.registerCheck<CommandProcessorCheck>(
diff --git a/clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt b/clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt
index 43e85b1407f21..6345e61b3b126 100644
--- a/clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt
@@ -15,6 +15,7 @@ add_clang_library(clangTidyBugproneModule STATIC
BugproneTidyModule.cpp
CapturingThisInMemberVariableCheck.cpp
CastingThroughVoidCheck.cpp
+ CerrnoCheck.cpp
ChainedComparisonCheck.cpp
CommandProcessorCheck.cpp
ComparePointerToMemberVirtualFunctionCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/bugprone/CerrnoCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/CerrnoCheck.cpp
new file mode 100644
index 0000000000000..8dbb685662084
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/bugprone/CerrnoCheck.cpp
@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "CerrnoCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+void CerrnoCheck::registerMatchers(MatchFinder *Finder) {
+ Finder->addMatcher(varDecl(hasType(asString("int")), hasName("errno"), hasExternalFormalLinkage()).bind("errnoDecl"), this);
+}
+
+void CerrnoCheck::check(const MatchFinder::MatchResult &Result) {
+ const auto *MatchedDecl = Result.Nodes.getNodeAs<VarDecl>("errnoDecl"); // NULL?
+ const SourceManager &SM = *Result.SourceManager;
+ const auto Location = MatchedDecl->getLocation();
+ const auto FileID = SM.getFileID(Location);
+
+ unsigned Line = SM.getSpellingLineNumber(MatchedDecl->getBeginLoc());
+
+ const auto Diag = diag(Location, "errno declaration detected, include cerrno instead")
+ << FixItHint::CreateRemoval(CharSourceRange::getCharRange(SM.translateLineCol(FileID, Line, 1), SM.translateLineCol(FileID, Line + 1, 1)));
+
+ if (alreadyInserted)
+ return;
+
+ Diag << FixItHint::CreateInsertion(SM.getLocForStartOfFile(FileID), "#include <cerrno>\n");
+ alreadyInserted = true;
+}
+
+} // namespace clang::tidy::bugprone
diff --git a/clang-tools-extra/clang-tidy/bugprone/CerrnoCheck.h b/clang-tools-extra/clang-tidy/bugprone/CerrnoCheck.h
new file mode 100644
index 0000000000000..7517acd28a49f
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/bugprone/CerrnoCheck.h
@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_BUGPRONE_CERRNOCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_CERRNOCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::bugprone {
+
+/// Warns if you declare an extern int variable named 'errno'.
+///
+/// For the user-facing documentation see:
+/// https://clang.llvm.org/extra/clang-tidy/checks/bugprone/cerrno.html
+class CerrnoCheck : public ClangTidyCheck {
+public:
+ CerrnoCheck(StringRef Name, ClangTidyContext *Context)
+ : ClangTidyCheck(Name, Context) {}
+ void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+ void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+ bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+ return LangOpts.CPlusPlus;
+ }
+private:
+ bool alreadyInserted = false;
+};
+
+} // namespace clang::tidy::bugprone
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_CERRNOCHECK_H
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 2581a9d3c5657..e3a19dffc931a 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -224,6 +224,11 @@ New checks
Finds assignments within selection statements.
+- New :doc:`bugprone-cerrno
+ <clang-tidy/checks/bugprone/cerrno>` check.
+
+ Warns if you declare an extern int variable named 'errno'.
+
- New :doc:`bugprone-missing-end-comparison
<clang-tidy/checks/bugprone/missing-end-comparison>` check.
diff --git a/clang-tools-extra/docs/clang-tidy/checks/bugprone/cerrno.rst b/clang-tools-extra/docs/clang-tidy/checks/bugprone/cerrno.rst
new file mode 100644
index 0000000000000..73ec1c76901af
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/bugprone/cerrno.rst
@@ -0,0 +1,17 @@
+.. title:: clang-tidy - bugprone-cerrno
+
+bugprone-cerrno
+===============
+
+Warns if you declare an ``extern int`` variable named ``errno`` instead of including ``<cerrno>``.
+It is able to fix the problem by removing the line of the declaration and inserting ``#include <cerrno>``
+at the top of the file.
+
+For further reading, see `the page of SEI CERT C Coding Standard
+<https://cmu-sei.github.io/secure-coding-standards/sei-cert-c-coding-standard/rules/miscellaneous-msc/msc38-c/>`_.
+
+Example:
+
+.. code-block:: c++
+
+ extern int errno;
diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index 2a44dc78fbc89..355401cbdccc6 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -87,6 +87,7 @@ Clang-Tidy Checks
:doc:`bugprone-branch-clone <bugprone/branch-clone>`,
:doc:`bugprone-capturing-this-in-member-variable <bugprone/capturing-this-in-member-variable>`,
:doc:`bugprone-casting-through-void <bugprone/casting-through-void>`,
+ :doc:`bugprone-cerrno <bugprone/cerrno>`, "Yes"
:doc:`bugprone-chained-comparison <bugprone/chained-comparison>`,
:doc:`bugprone-command-processor <bugprone/command-processor>`,
:doc:`bugprone-compare-pointer-to-member-virtual-function <bugprone/compare-pointer-to-member-virtual-function>`,
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/cerrno.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/cerrno.cpp
new file mode 100644
index 0000000000000..40109d31aa26b
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/cerrno.cpp
@@ -0,0 +1,25 @@
+// RUN: %check_clang_tidy %s bugprone-cerrno %t
+
+namespace cerrno_test_0 {
+ extern int errno;
+ // CHECK-MESSAGES: :[[@LINE-1]]:16: warning: errno declaration detected, include cerrno instead [bugprone-cerrno]
+ // CHECK-FIXES: {{^}}{{$}}
+} // namespace cerrno_test_0
+
+namespace cerrno_test_1 {
+ extern "C" int errno;
+ // CHECK-MESSAGES: :[[@LINE-1]]:20: warning: errno declaration detected, include cerrno instead [bugprone-cerrno]
+ // CHECK-FIXES: {{^}}{{$}}
+} // namespace cerrno_test_1
+
+namespace cerrno_test_2 { // all cases should be ignored in this namespace
+ extern bool errno;
+
+ void foo(int errno) {}
+
+ int fooo()
+ {
+ int errno = 0;
+ return errno;
+ }
+} // namespace cerrno_test_2
``````````
</details>
https://github.com/llvm/llvm-project/pull/213015
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