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[clang-tidy] Option to ignore anonymous namespaces in avoid-non-const-global-variables (#93827)
Add an option to ignore warnings for cppcoreguidelines avoid-non-const-global-variables. Understandably, the core guidelines discourage non const global variables, even at the TU level (see isocpp/CppCoreGuidelines#2195). However, having a small TU with an interface that uses a non const variable from an anonymous namespace can be a valid choice. This adds an option that disables the warning just for anonymous namespaces, i.e. at the file level. The default is still to show a warning, just as before.
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‎clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.cpp

Lines changed: 16 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -7,21 +7,30 @@
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//===----------------------------------------------------------------------===//
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#include "AvoidNonConstGlobalVariablesCheck.h"
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#include "clang/AST/ASTContext.h"
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#include "clang/ASTMatchers/ASTMatchFinder.h"
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#include "clang/ASTMatchers/ASTMatchers.h"
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using namespace clang::ast_matchers;
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namespace clang::tidy::cppcoreguidelines {
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AvoidNonConstGlobalVariablesCheck::AvoidNonConstGlobalVariablesCheck(
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StringRef Name, ClangTidyContext *Context)
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: ClangTidyCheck(Name, Context),
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AllowInternalLinkage(Options.get("AllowInternalLinkage", false)) {}
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void AvoidNonConstGlobalVariablesCheck::registerMatchers(MatchFinder *Finder) {
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auto NamespaceMatcher = AllowInternalLinkage
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? namespaceDecl(unless(isAnonymous()))
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: namespaceDecl();
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auto GlobalContext =
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varDecl(hasGlobalStorage(),
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hasDeclContext(anyOf(namespaceDecl(), translationUnitDecl())));
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hasDeclContext(anyOf(NamespaceMatcher, translationUnitDecl())));
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auto GlobalVariable = varDecl(
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GlobalContext,
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AllowInternalLinkage ? varDecl(unless(isStaticStorageClass()))
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: varDecl(),
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unless(anyOf(
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isConstexpr(), hasType(isConstQualified()),
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hasType(referenceType())))); // References can't be changed, only the
@@ -43,7 +52,6 @@ void AvoidNonConstGlobalVariablesCheck::registerMatchers(MatchFinder *Finder) {
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void AvoidNonConstGlobalVariablesCheck::check(
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const MatchFinder::MatchResult &Result) {
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if (const auto *Variable =
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Result.Nodes.getNodeAs<VarDecl>("non-const_variable")) {
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diag(Variable->getLocation(), "variable %0 is non-const and globally "
@@ -63,4 +71,9 @@ void AvoidNonConstGlobalVariablesCheck::check(
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}
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}
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void AvoidNonConstGlobalVariablesCheck::storeOptions(
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ClangTidyOptions::OptionMap &Opts) {
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Options.store(Opts, "AllowInternalLinkage", AllowInternalLinkage);
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}
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} // namespace clang::tidy::cppcoreguidelines

‎clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.h

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -20,10 +20,13 @@ namespace clang::tidy::cppcoreguidelines {
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/// http://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines/avoid-non-const-global-variables.html
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class AvoidNonConstGlobalVariablesCheck : public ClangTidyCheck {
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public:
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AvoidNonConstGlobalVariablesCheck(StringRef Name, ClangTidyContext *Context)
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: ClangTidyCheck(Name, Context) {}
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AvoidNonConstGlobalVariablesCheck(StringRef Name, ClangTidyContext *Context);
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void registerMatchers(ast_matchers::MatchFinder *Finder) override;
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void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
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void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
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private:
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const bool AllowInternalLinkage;
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};
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} // namespace clang::tidy::cppcoreguidelines

‎clang-tools-extra/docs/ReleaseNotes.rst

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Original file line numberDiff line numberDiff line change
@@ -269,6 +269,11 @@ Changes in existing checks
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<clang-tidy/checks/bugprone/use-after-move>` check to also handle
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calls to ``std::forward``.
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- Improved :doc:`cppcoreguidelines-avoid-non-const-global-variables
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<clang-tidy/checks/cppcoreguidelines/avoid-non-const-global-variables>` check
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with a new option `AllowInternalLinkage` to disable the warning for variables
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with internal linkage.
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- Improved :doc:`cppcoreguidelines-macro-usage
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<clang-tidy/checks/cppcoreguidelines/macro-usage>` check by ignoring macro with
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hash preprocessing token.

‎clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/avoid-non-const-global-variables.rst

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -41,3 +41,11 @@ The variables ``a``, ``c``, ``c_ptr1``, ``c_const_ptr`` and ``c_reference``
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will all generate warnings since they are either a non-const globally accessible
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variable, a pointer or a reference providing global access to non-const data
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or both.
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Options
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-------
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.. option:: AllowInternalLinkage
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When set to `true`, static non-const variables and variables in anonymous
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namespaces will not generate a warning. The default value is `false`.

‎clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-non-const-global-variables.cpp

Lines changed: 17 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,6 @@
1-
// RUN: %check_clang_tidy %s cppcoreguidelines-avoid-non-const-global-variables %t
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// RUN: %check_clang_tidy %s -check-suffixes=,DEFAULT cppcoreguidelines-avoid-non-const-global-variables %t
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// RUN: %check_clang_tidy %s -check-suffixes=,INTERNAL-LINKAGE cppcoreguidelines-avoid-non-const-global-variables %t -- \
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// RUN: -config="{CheckOptions: {cppcoreguidelines-avoid-non-const-global-variables.AllowInternalLinkage : 'true'}}"
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int nonConstInt = 0;
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// CHECK-MESSAGES: :[[@LINE-1]]:5: warning: variable 'nonConstInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
@@ -38,9 +40,16 @@ int function() {
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namespace {
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int nonConstAnonymousNamespaceInt = 0;
41-
// CHECK-MESSAGES: :[[@LINE-1]]:5: warning: variable 'nonConstAnonymousNamespaceInt' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
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// 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]
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// 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]
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} // namespace
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static int nonConstStaticInt = 0;
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// 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]
49+
// 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]
50+
51+
static const int constStaticInt = 0;
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4453
class DummyClass {
4554
public:
4655
int nonConstPublicMemberVariable = 0;
@@ -126,7 +135,8 @@ const DummyEnum constNamespaceEnumInstance = DummyEnum::first;
126135
namespace {
127136
DummyEnum nonConstAnonymousNamespaceEnumInstance = DummyEnum::first;
128137
}
129-
// CHECK-MESSAGES: :[[@LINE-2]]:11: warning: variable 'nonConstAnonymousNamespaceEnumInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
138+
// 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]
139+
// 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]
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// CHECKING FOR NON-CONST GLOBAL STRUCT ///////////////////////////////////////
132142
struct DummyStruct {
@@ -169,7 +179,8 @@ const DummyStruct constNamespaceDummyStructInstance;
169179
namespace {
170180
DummyStruct nonConstAnonymousNamespaceStructInstance;
171181
}
172-
// CHECK-MESSAGES: :[[@LINE-2]]:13: warning: variable 'nonConstAnonymousNamespaceStructInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
182+
// 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]
183+
// 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]
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// CHECKING FOR NON-CONST GLOBAL UNION ////////////////////////////////////////
175186
union DummyUnion {
@@ -209,7 +220,8 @@ const DummyUnion constNamespaceDummyUnionInstance = {0x0};
209220
namespace {
210221
DummyUnion nonConstAnonymousNamespaceUnionInstance = {0x0};
211222
}
212-
// CHECK-MESSAGES: :[[@LINE-2]]:12: warning: variable 'nonConstAnonymousNamespaceUnionInstance' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
223+
// 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]
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// 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]
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// CHECKING FOR NON-CONST GLOBAL FUNCTION POINTER /////////////////////////////
215227
int dummyFunction() {

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