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[clang-tidy] make misc-const-correctness work with auto variables and lambdas #157319

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[clang-tidy] make misc-const-correctness work with auto variables and lambdas #157319

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e28e9e2
[clang-tidy] make `misc-const-correctness` work with `auto` variables…
localspook Sep 7, 2025
07a85c1
make comment less confusing
localspook Sep 7, 2025
c8043f8
add tests ensuring rvalue references aren't diagnosed
localspook Sep 7, 2025
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12 changes: 3 additions & 9 deletions clang-tools-extra/clang-tidy/misc/ConstCorrectnessCheck.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -98,17 +98,13 @@ void ConstCorrectnessCheck::registerMatchers(MatchFinder *Finder) {
hasType(referenceType(pointee(hasCanonicalType(templateTypeParmType())))),
hasType(referenceType(pointee(substTemplateTypeParmType()))));

auto AllowedTypeDecl = namedDecl(
const auto AllowedTypeDecl = namedDecl(
anyOf(matchers::matchesAnyListedName(AllowedTypes), usingShadowDecl()));

const auto AllowedType = hasType(qualType(
anyOf(hasDeclaration(AllowedTypeDecl), references(AllowedTypeDecl),
pointerType(pointee(hasDeclaration(AllowedTypeDecl))))));

const auto AutoTemplateType = varDecl(
anyOf(hasType(autoType()), hasType(referenceType(pointee(autoType()))),
hasType(pointerType(pointee(autoType())))));

const auto FunctionPointerRef =
hasType(hasCanonicalType(referenceType(pointee(functionType()))));

Expand All @@ -117,10 +113,8 @@ void ConstCorrectnessCheck::registerMatchers(MatchFinder *Finder) {
const auto LocalValDecl = varDecl(
isLocal(), hasInitializer(anything()),
unless(anyOf(ConstType, ConstReference, TemplateType,
hasInitializer(isInstantiationDependent()), AutoTemplateType,
RValueReference, FunctionPointerRef,
hasType(cxxRecordDecl(isLambda())), isImplicit(),
AllowedType)));
hasInitializer(isInstantiationDependent()), RValueReference,
FunctionPointerRef, isImplicit(), AllowedType)));

// Match the function scope for which the analysis of all local variables
// shall be run.
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4 changes: 4 additions & 0 deletions clang-tools-extra/docs/ReleaseNotes.rst
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Expand Up @@ -185,6 +185,10 @@ Changes in existing checks
adding an option to allow pointer arithmetic via prefix/postfix increment or
decrement operators.

- Improved :doc:`misc-const-correctness
<clang-tidy/checks/misc/const-correctness>` check to diagnose
variables declared with ``auto``.
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I'm not mentioning lambdas because lambdas must be declared with auto anyway.


- Improved :doc:`misc-header-include-cycle
<clang-tidy/checks/misc/header-include-cycle>` check performance.

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6 changes: 5 additions & 1 deletion clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-pointer-as-values.cpp
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Expand Up @@ -33,7 +33,9 @@ void range_for() {
int *p_local2[2] = {nullptr, nullptr};
// CHECK-MESSAGES: [[@LINE-1]]:3: warning: variable 'p_local2' of type 'int *[2]' can be declared 'const'
// CHECK-FIXES: int *const p_local2[2]
for (const auto *con_ptr : p_local2) {
for (const auto *p_local3 : p_local2) {
// CHECK-MESSAGES: [[@LINE-1]]:8: warning: variable 'p_local3' of type 'const int *' can be declared 'const'
// CHECK-FIXES: for (const auto *const p_local3 : p_local2)
}

}
Expand Down Expand Up @@ -62,6 +64,8 @@ void EmitProtocolMethodList(T &&Methods) {
// CHECK-FIXES: SmallVector<const int *> const p_local0
SmallVector<const int *> np_local0;
for (const auto *I : Methods) {
// CHECK-MESSAGES: [[@LINE-1]]:8: warning: variable 'I' of type 'const int *' can be declared 'const'
// CHECK-FIXES: for (const auto *const I : Methods)
if (I == nullptr)
np_local0.push_back(I);
}
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8 changes: 7 additions & 1 deletion clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-templates.cpp
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Expand Up @@ -9,9 +9,15 @@
template <typename T>
void type_dependent_variables() {
T value = 42;
auto &ref = value;
T &templateRef = value;

auto &ref = value;
// CHECK-MESSAGES:[[@LINE-1]]:3: warning: variable 'ref' of type 'int &' can be declared 'const'
// CHECK-FIXES: auto const&ref = value;
// FIXME: This is a false positive, the reference points to a template type
// and needs to be excluded from analysis. See the 'more_template_locals()'
// test in 'const-correctness-values.cpp' for more examples of the problem.
Comment on lines +17 to +19
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VarDecl::getIinit -> Expr::isTypeDependent should do the trick


int value_int = 42;
// CHECK-MESSAGES:[[@LINE-1]]:3: warning: variable 'value_int' of type 'int' can be declared 'const'
// CHECK-FIXES: int const value_int = 42;
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6 changes: 0 additions & 6 deletions clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-transform-values.cpp
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Expand Up @@ -14,12 +14,6 @@ int scoped;
float np_scoped = 1; // namespace variables are like globals
} // namespace foo

// Lambdas should be ignored, because they do not follow the normal variable
// semantic (e.g. the type is only known to the compiler).
void lambdas() {
auto Lambda = [](int i) { return i < 0; };
}

void some_function(double, wchar_t);

void some_function(double np_arg0, wchar_t np_arg1) {
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33 changes: 29 additions & 4 deletions clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-values.cpp
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Expand Up @@ -27,10 +27,19 @@ int np_anonymous_global;
int p_anonymous_global = 43;
} // namespace

// Lambdas should be ignored, because they do not follow the normal variable
// semantic (e.g. the type is only known to the compiler).
void lambdas() {
auto Lambda = [](int i) { return i < 0; };
// CHECK-MESSAGES: [[@LINE-1]]:3: warning: variable 'Lambda' of type '{{.*}}' can be declared 'const'
// CHECK-FIXES: auto const Lambda

auto LambdaWithMutableCallOperator = []() mutable {};
LambdaWithMutableCallOperator();

int x = 0;
auto LambdaModifyingCapture = [&x] { ++x; };
// CHECK-MESSAGES: [[@LINE-1]]:3: warning: variable 'LambdaModifyingCapture' of type '{{.*}}' can be declared 'const'
// CHECK-FIXES: auto const LambdaModifyingCapture
LambdaModifyingCapture();
}

void some_function(double, wchar_t);
Expand Down Expand Up @@ -85,6 +94,11 @@ void ignore_reference_to_pointers() {
int *&np_local1 = np_local0;
}

void ignore_rvalue_references() {
int &&np_local0 = 42;
auto &&np_local1 = 42;
}

void some_lambda_environment_capture_all_by_reference(double np_arg0) {
int np_local0 = 0;
int p_local0 = 1;
Expand Down Expand Up @@ -965,14 +979,23 @@ template <typename T>
T *return_ptr() { return &return_ref<T>(); }

void auto_usage_variants() {
auto auto_int = int{};
// CHECK-MESSAGES:[[@LINE-1]]:3: warning: variable 'auto_int' of type 'int' can be declared 'const'
// CHECK-FIXES: auto const auto_int

auto auto_val0 = int{};
// CHECK-FIXES-NOT: auto const auto_val0
auto &auto_val1 = auto_val0;
// CHECK-MESSAGES:[[@LINE-1]]:3: warning: variable 'auto_val1' of type 'int &' can be declared 'const'
// CHECK-FIXES: auto const&auto_val1
auto *auto_val2 = &auto_val0;

auto auto_ref0 = return_ref<int>();
// CHECK-FIXES-NOT: auto const auto_ref0
auto &auto_ref1 = return_ref<int>(); // Bad
// CHECK-MESSAGES:[[@LINE-1]]:3: warning: variable 'auto_ref0' of type 'int' can be declared 'const'
// CHECK-FIXES: auto const auto_ref0
auto &auto_ref1 = return_ref<int>();
// CHECK-MESSAGES:[[@LINE-1]]:3: warning: variable 'auto_ref1' of type 'int &' can be declared 'const'
// CHECK-FIXES: auto const&auto_ref1
auto *auto_ref2 = return_ptr<int>();

auto auto_ptr0 = return_ptr<int>();
Expand All @@ -984,6 +1007,8 @@ void auto_usage_variants() {
auto auto_td0 = MyTypedef{};
// CHECK-FIXES-NOT: auto const auto_td0
auto &auto_td1 = auto_td0;
// CHECK-MESSAGES:[[@LINE-1]]:3: warning: variable 'auto_td1' of type 'MyTypedef &' (aka 'int &') can be declared 'const'
// CHECK-FIXES: auto const&auto_td1
auto *auto_td2 = &auto_td0;
}

Expand Down