[clang-tools-extra] [clang-tidy] Allow thread-local variables in avoid-non-const-global-variables (PR #164442)

Sirui Mu via cfe-commits cfe-commits at lists.llvm.org
Tue Oct 21 08:22:55 PDT 2025 

https://github.com/Lancern created https://github.com/llvm/llvm-project/pull/164442

This patch adds an option named `AllowThreadLocal` to the `cppcoreguidelines-avoid-non-const-global-variables` check. When set to true, the option suppresses warnings generated for non-const global variables with thread-local storage duration. By default, the option is set to false.

>From 0e5e21fb7e9b6d8568e5a20a153c76fa3ff1743e Mon Sep 17 00:00:00 2001
From: Sirui Mu <msrlancern at gmail.com>
Date: Tue, 21 Oct 2025 23:09:05 +0800
Subject: [PATCH] [clang-tidy] Allow thread-local variables in
 avoid-non-const-global-variables

This patch adds an option named `AllowThreadLocal` to the
`cppcoreguidelines-avoid-non-const-global-variables` check. When set to true,
the option suppresses warnings generated for non-const global variables with
thread-local storage duration. By default, the option is set to false.
---
 .../AvoidNonConstGlobalVariablesCheck.cpp          |  5 ++++-
 .../AvoidNonConstGlobalVariablesCheck.h            |  1 +
 clang-tools-extra/docs/ReleaseNotes.rst            |  5 +++++
 .../avoid-non-const-global-variables.rst           |  5 +++++
 .../avoid-non-const-global-variables.cpp           | 14 ++++++++++++++
 5 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.cpp
index f0e66e44690b2..2c0baa5716954 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.cpp
@@ -17,7 +17,8 @@ namespace clang::tidy::cppcoreguidelines {
 AvoidNonConstGlobalVariablesCheck::AvoidNonConstGlobalVariablesCheck(
     StringRef Name, ClangTidyContext *Context)
     : ClangTidyCheck(Name, Context),
-      AllowInternalLinkage(Options.get("AllowInternalLinkage", false)) {}
+      AllowInternalLinkage(Options.get("AllowInternalLinkage", false)),
+      AllowThreadLocal(Options.get("AllowThreadLocal", false)) {}
 
 void AvoidNonConstGlobalVariablesCheck::registerMatchers(MatchFinder *Finder) {
   auto NamespaceMatcher = AllowInternalLinkage
@@ -31,6 +32,8 @@ void AvoidNonConstGlobalVariablesCheck::registerMatchers(MatchFinder *Finder) {
       GlobalContext,
       AllowInternalLinkage ? varDecl(unless(isStaticStorageClass()))
                            : varDecl(),
+      AllowThreadLocal ? varDecl(unless(hasThreadStorageDuration()))
+                       : varDecl(),
       unless(anyOf(
           isConstexpr(), hasType(isConstQualified()),
           hasType(referenceType())))); // References can't be changed, only the
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.h b/clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.h
index 5e7c968b12f97..d8f2a733e3b01 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.h
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.h
@@ -27,6 +27,7 @@ class AvoidNonConstGlobalVariablesCheck : public ClangTidyCheck {
 
 private:
   const bool AllowInternalLinkage;
+  const bool AllowThreadLocal;
 };
 
 } // namespace clang::tidy::cppcoreguidelines
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 8a0151f567c24..58bcf92a75834 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -316,6 +316,11 @@ Changes in existing checks
   an additional matcher that generalizes the copy-and-swap idiom pattern
   detection.
 
+- Improved :doc:`cppcoreguidelines-avoid-non-const-global-variables
+  <clang-tidy/checks/cppcoreguidelines/avoid-non-const-global-variables>` check
+  by adding a new option ``AllowThreadLocal`` that suppresses warnings on
+  non-const global variables with thread-local storage duration.
+
 - Improved :doc:`cppcoreguidelines-init-variables
   <clang-tidy/checks/cppcoreguidelines/init-variables>` check by fixing the
   insertion location for function pointers with multiple parameters.
diff --git a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/avoid-non-const-global-variables.rst b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/avoid-non-const-global-variables.rst
index 8da284ca13e3d..3d5fef3a07dca 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/avoid-non-const-global-variables.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/avoid-non-const-global-variables.rst
@@ -49,3 +49,8 @@ Options
 
    When set to `true`, static non-const variables and variables in anonymous
    namespaces will not generate a warning. The default value is `false`.
+
+.. option:: AllowThreadLocal
+
+   When set to `true`, non-const global variables with thread-local storage
+   duration will not generate a warning. The default value is `false`.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-non-const-global-variables.cpp b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-non-const-global-variables.cpp
index 334332def216f..30bdd68a21b84 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-non-const-global-variables.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-non-const-global-variables.cpp
@@ -1,6 +1,8 @@
 // RUN: %check_clang_tidy %s -check-suffixes=,DEFAULT cppcoreguidelines-avoid-non-const-global-variables %t
 // RUN: %check_clang_tidy %s -check-suffixes=,INTERNAL-LINKAGE cppcoreguidelines-avoid-non-const-global-variables %t -- \
 // RUN: -config="{CheckOptions: {cppcoreguidelines-avoid-non-const-global-variables.AllowInternalLinkage : 'true'}}"
+// RUN: %check_clang_tidy %s -check-suffixes=,THREAD-LOCAL cppcoreguidelines-avoid-non-const-global-variables %t -- \
+// RUN: -config="{CheckOptions: {cppcoreguidelines-avoid-non-const-global-variables.AllowThreadLocal : 'true'}}"
 
 int nonConstInt = 0;
 // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: variable 'nonConstInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
@@ -42,14 +44,23 @@ namespace {
 int nonConstAnonymousNamespaceInt = 0;
 // CHECK-MESSAGES-DEFAULT: :[[@LINE-1]]:5: warning: variable 'nonConstAnonymousNamespaceInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 // CHECK-MESSAGES-INTERNAL-LINKAGE-NOT: :[[@LINE-2]]:5: warning: variable 'nonConstAnonymousNamespaceInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
+// CHECK-MESSAGES-THREAD-LOCAL: :[[@LINE-3]]:5: warning: variable 'nonConstAnonymousNamespaceInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 } // namespace
 
 static int nonConstStaticInt = 0;
 // CHECK-MESSAGES-DEFAULT: :[[@LINE-1]]:12: warning: variable 'nonConstStaticInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 // CHECK-MESSAGES-INTERNAL-LINKAGE-NOT: :[[@LINE-2]]:12: warning: variable 'nonConstStaticInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
+// CHECK-MESSAGES-THREAD-LOCAL: :[[@LINE-3]]:12: warning: variable 'nonConstStaticInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 
 static const int constStaticInt = 0;
 
+thread_local int threadLocalInt = 0;
+// CHECK-MESSAGES-DEFAULT: :[[@LINE-1]]:18: warning: variable 'threadLocalInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
+// CHECK-MESSAGES-INTERNAL-LINKAGE: :[[@LINE-2]]:18: warning: variable 'threadLocalInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
+// CHECK-MESSAGES-THREAD-LOCAL-NOT: :[[@LINE-3]]:18: warning: variable 'threadLocalInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
+
+thread_local const int threadLocalConstInt = 0;
+
 class DummyClass {
 public:
   int nonConstPublicMemberVariable = 0;
@@ -137,6 +148,7 @@ DummyEnum nonConstAnonymousNamespaceEnumInstance = DummyEnum::first;
 }
 // CHECK-MESSAGES-DEFAULT: :[[@LINE-2]]:11: warning: variable 'nonConstAnonymousNamespaceEnumInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 // CHECK-MESSAGES-INTERNAL-LINKAGE-NOT: :[[@LINE-2]]:11: warning: variable 'nonConstAnonymousNamespaceEnumInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
+// CHECK-MESSAGES-THREAD-LOCAL: :[[@LINE-4]]:11: warning: variable 'nonConstAnonymousNamespaceEnumInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 
 // CHECKING FOR NON-CONST GLOBAL STRUCT ///////////////////////////////////////
 struct DummyStruct {
@@ -181,6 +193,7 @@ DummyStruct nonConstAnonymousNamespaceStructInstance;
 }
 // CHECK-MESSAGES-DEFAULT: :[[@LINE-2]]:13: warning: variable 'nonConstAnonymousNamespaceStructInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 // CHECK-MESSAGES-INTERNAL-LINKAGE-NOT: :[[@LINE-2]]:11: warning: variable 'nonConstAnonymousNamespaceEnumInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
+// CHECK-MESSAGES-THREAD-LOCAL: :[[@LINE-4]]:13: warning: variable 'nonConstAnonymousNamespaceStructInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 
 // CHECKING FOR NON-CONST GLOBAL UNION ////////////////////////////////////////
 union DummyUnion {
@@ -222,6 +235,7 @@ DummyUnion nonConstAnonymousNamespaceUnionInstance = {0x0};
 }
 // CHECK-MESSAGES-DEFAULT: :[[@LINE-2]]:12: warning: variable 'nonConstAnonymousNamespaceUnionInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 // CHECK-MESSAGES-INTERNAL-LINKAGE-NOT: :[[@LINE-3]]:12: warning: variable 'nonConstAnonymousNamespaceUnionInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
+// CHECK-MESSAGES-THREAD-LOCAL: :[[@LINE-4]]:12: warning: variable 'nonConstAnonymousNamespaceUnionInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 
 // CHECKING FOR NON-CONST GLOBAL FUNCTION POINTER /////////////////////////////
 int dummyFunction() {

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