https://github.com/stmuench updated
https://github.com/llvm/llvm-project/pull/132924
>From 9d8acb1132385fb649bb61a872f32ce1d11530b1 Mon Sep 17 00:00:00 2001
From: stmuench <stmue...@gmx.net>
Date: Tue, 25 Mar 2025 12:38:53 +0100
Subject: [PATCH] [clang-tidy] do not diagn. array types in implicit templ.
instantiations
So far, the clang-tidy check `modernize-avoid-c-arrays` also diagnosed
array types for type template parameters even though no actual array
type got written there but it got deduced to one. In such case, there
is nothing a developer can do at that location to fix the diagnostic.
Since actually, the location where the template got instantiated
would have to be adjusted. And this is in most cases some totally
distant code where implementers of a template do not have access to.
Also adding suppressions to the declaration of the template is not an
option since that would clutter the code unnecessarily and is in many
cases also simply not possible. Hence, we propose to not diagnose any
occurrence of an array type in an implicit instantiation of a template
but rather at the point where template arguments involve array types.
---
.../modernize/AvoidCArraysCheck.cpp | 75 ++++++-
clang-tools-extra/docs/ReleaseNotes.rst | 4 +
.../avoid-c-arrays-ignores-strings.cpp | 12 ++
.../checkers/modernize/avoid-c-arrays.cpp | 192 ++++++++++++++++++
4 files changed, 277 insertions(+), 6 deletions(-)
diff --git a/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp
b/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp
index ee70911dff1d5..c755a1dfffe68 100644
--- a/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp
@@ -39,6 +39,51 @@ AST_MATCHER(clang::ParmVarDecl, isArgvOfMain) {
return FD ? FD->isMain() : false;
}
+AST_MATCHER(clang::TypeLoc, isWithinImplicitTemplateInstantiation) {
+ const auto IsImplicitTemplateInstantiation = [](const auto *Node) {
+ return (Node != nullptr) &&
+ (Node->getTemplateSpecializationKind() ==
TSK_ImplicitInstantiation);
+ };
+
+ DynTypedNodeList ParentNodes = Finder->getASTContext().getParents(Node);
+ const clang::NamedDecl *ParentDecl = nullptr;
+ while (!ParentNodes.empty()) {
+ const DynTypedNode &ParentNode = ParentNodes[0];
+ if (IsImplicitTemplateInstantiation(
+ ParentNode.template get<clang::CXXRecordDecl>()) ||
+ IsImplicitTemplateInstantiation(
+ ParentNode.template get<clang::FunctionDecl>()) ||
+ IsImplicitTemplateInstantiation(
+ ParentNode.template get<clang::VarDecl>()))
+ return true;
+
+ // in case of a `NamedDecl` as parent node, it is more efficient to proceed
+ // with the upward traversal via DeclContexts (see below) instead of via
+ // parent nodes
+ if (ParentDecl = ParentNode.template get<clang::NamedDecl>())
+ break;
+
+ ParentNodes = Finder->getASTContext().getParents(ParentNode);
+ }
+
+ if (ParentDecl != nullptr) {
+ const clang::DeclContext *DeclContext = ParentDecl->getDeclContext();
+ while (DeclContext != nullptr) {
+ for (const clang::Decl *Decl : DeclContext->decls()) {
+ if (IsImplicitTemplateInstantiation(
+ dyn_cast<clang::CXXRecordDecl>(Decl)) ||
+ IsImplicitTemplateInstantiation(
+ dyn_cast<clang::FunctionDecl>(Decl)) ||
+ IsImplicitTemplateInstantiation(dyn_cast<clang::VarDecl>(Decl)))
+ return true;
+ }
+ DeclContext = DeclContext->getParent();
+ }
+ }
+
+ return false;
+}
+
} // namespace
AvoidCArraysCheck::AvoidCArraysCheck(StringRef Name, ClangTidyContext *Context)
@@ -66,22 +111,38 @@ void AvoidCArraysCheck::registerMatchers(MatchFinder
*Finder) {
hasParent(varDecl(isExternC())),
hasParent(fieldDecl(
hasParent(recordDecl(isExternCContext())))),
- hasAncestor(functionDecl(isExternC())))),
+ hasAncestor(functionDecl(isExternC())),
+ isWithinImplicitTemplateInstantiation())),
IgnoreStringArrayIfNeededMatcher)
.bind("typeloc"),
this);
+
+ Finder->addMatcher(
+ templateArgumentLoc(hasTypeLoc(
+ typeLoc(hasType(arrayType())).bind("template_arg_array_typeloc"))),
+ this);
}
void AvoidCArraysCheck::check(const MatchFinder::MatchResult &Result) {
- const auto *ArrayType = Result.Nodes.getNodeAs<TypeLoc>("typeloc");
+ TypeLoc ArrayTypeLoc{};
+
+ if (const auto *MatchedTypeLoc = Result.Nodes.getNodeAs<TypeLoc>("typeloc"))
+ ArrayTypeLoc = *MatchedTypeLoc;
+
+ if (const auto *TemplateArgArrayTypeLoc =
+ Result.Nodes.getNodeAs<TypeLoc>("template_arg_array_typeloc"))
+ ArrayTypeLoc = *TemplateArgArrayTypeLoc;
+
+ assert(!ArrayTypeLoc.isNull());
+
const bool IsInParam =
Result.Nodes.getNodeAs<ParmVarDecl>("param_decl") != nullptr;
- const bool IsVLA = ArrayType->getTypePtr()->isVariableArrayType();
+ const bool IsVLA = ArrayTypeLoc.getTypePtr()->isVariableArrayType();
enum class RecommendType { Array, Vector, Span };
llvm::SmallVector<const char *> RecommendTypes{};
if (IsVLA) {
RecommendTypes.push_back("'std::vector'");
- } else if (ArrayType->getTypePtr()->isIncompleteArrayType() && IsInParam) {
+ } else if (ArrayTypeLoc.getTypePtr()->isIncompleteArrayType() && IsInParam) {
// in function parameter, we also don't know the size of
// IncompleteArrayType.
if (Result.Context->getLangOpts().CPlusPlus20)
@@ -93,9 +154,11 @@ void AvoidCArraysCheck::check(const
MatchFinder::MatchResult &Result) {
} else {
RecommendTypes.push_back("'std::array'");
}
- diag(ArrayType->getBeginLoc(),
+
+ diag(ArrayTypeLoc.getBeginLoc(),
"do not declare %select{C-style|C VLA}0 arrays, use %1 instead")
- << IsVLA << llvm::join(RecommendTypes, " or ");
+ << IsVLA << llvm::join(RecommendTypes, " or ")
+ << ArrayTypeLoc.getSourceRange();
}
} // namespace clang::tidy::modernize
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst
b/clang-tools-extra/docs/ReleaseNotes.rst
index 388979d9577ba..590ed8780ef27 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -183,6 +183,10 @@ Changes in existing checks
- Improved :doc:`misc-header-include-cycle
<clang-tidy/checks/misc/header-include-cycle>` check performance.
+- Improved :doc:`modernize-avoid-c-arrays
+ <clang-tidy/checks/modernize/avoid-c-arrays>` to not diagnose array types
+ which are part of an implicit instantiation of a template.
+
- Improved :doc:`modernize-use-designated-initializers
<clang-tidy/checks/modernize/use-designated-initializers>` check to
suggest using designated initializers for aliased aggregate types.
diff --git
a/clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays-ignores-strings.cpp
b/clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays-ignores-strings.cpp
index 906663828a547..18458bd47d347 100644
---
a/clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays-ignores-strings.cpp
+++
b/clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays-ignores-strings.cpp
@@ -7,3 +7,15 @@ const char array[] = {'n', 'a', 'm', 'e', '\0'};
void takeCharArray(const char name[]);
// CHECK-MESSAGES: :[[@LINE-1]]:26: warning: do not declare C-style arrays,
use 'std::array' or 'std::vector' instead [modernize-avoid-c-arrays]
+
+template <typename T = const char[10], typename U = char[10], char[10]>
+// CHECK-MESSAGES: :[[@LINE-1]]:30: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+// CHECK-MESSAGES: :[[@LINE-2]]:53: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+// CHECK-MESSAGES: :[[@LINE-3]]:63: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+void func() {}
+
+template <typename T = const char[], typename U = char[], char[]>
+// CHECK-MESSAGES: :[[@LINE-1]]:30: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+// CHECK-MESSAGES: :[[@LINE-2]]:51: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+// CHECK-MESSAGES: :[[@LINE-3]]:59: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+void fun() {}
diff --git
a/clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays.cpp
b/clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays.cpp
index 14eb2852c639a..95e04d53eb6ac 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays.cpp
@@ -32,7 +32,14 @@ array<int[4], 2> d;
using k = int[4];
// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: do not declare C-style arrays,
use 'std::array' instead
+k ak;
+// no diagnostic expected here since no concrete C-style array type is written
here
+
array<k, 2> dk;
+// no diagnostic expected here since no concrete C-style array type is written
here
+
+array<decltype(ak), 3> ek;
+// no diagnostic expected here since no concrete C-style array type is written
here
template <typename T>
class unique_ptr {
@@ -92,3 +99,188 @@ const char name[] = "Some string";
void takeCharArray(const char name[]);
// CHECK-MESSAGES: :[[@LINE-1]]:26: warning: do not declare C-style arrays,
use 'std::array' or 'std::vector' instead [modernize-avoid-c-arrays]
+
+namespace std {
+ template<class T, class U>
+ struct is_same { constexpr static bool value{false}; };
+
+ template<class T>
+ struct is_same<T, T> { constexpr static bool value{true}; };
+
+ template<class T, class U>
+ constexpr bool is_same_v = is_same<T, U>::value;
+
+ template<class T> struct remove_const { typedef T type; };
+ template<class T> struct remove_const<const T> { typedef T type; };
+
+ template<class T>
+ using remove_const_t = typename remove_const<T>::type;
+
+ template<bool B, class T = void> struct enable_if {};
+ template<class T> struct enable_if<true, T> { typedef T type; };
+
+ template< bool B, class T = void >
+ using enable_if_t = typename enable_if<B, T>::type;
+}
+
+// within below template decl, no array type findings are expected within the
template parameter declarations since not a single C-style array type got
written explicitly
+template <typename T,
+ bool = std::is_same_v<T, int>,
+ bool = std::is_same<T, int>::value,
+ bool = std::is_same_v<std::remove_const_t<T>, int>,
+ bool = std::is_same<std::remove_const_t<T>, int>::value,
+ bool = std::is_same_v<typename std::remove_const<T>::type, int>,
+ bool = std::is_same<typename std::remove_const<T>::type, int>::value,
+ std::enable_if_t<not(std::is_same_v<std::remove_const_t<T>, int>) &&
not(std::is_same_v<typename std::remove_const<T>::type, char>), bool> = true,
+ typename std::enable_if<not(std::is_same_v<std::remove_const_t<T>,
int>) && not(std::is_same_v<typename std::remove_const<T>::type, char>),
bool>::type = true,
+ typename =
std::enable_if_t<not(std::is_same_v<std::remove_const_t<T>, int>) &&
not(std::is_same_v<typename std::remove_const<T>::type, char>)>,
+ typename = typename std::remove_const<T>::type,
+ typename = std::remove_const_t<T>>
+class MyClassTemplate {
+ public:
+ // here, however, plenty of array type findings are expected for below
template parameter declarations since C-style array types are written explicitly
+ template <typename U = T,
+ bool = std::is_same_v<U, int[]>,
+ // CHECK-MESSAGES: :[[@LINE-1]]:38: warning: do not declare
C-style arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ bool = std::is_same<U, int[10]>::value,
+ // CHECK-MESSAGES: :[[@LINE-1]]:36: warning: do not declare
C-style arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ std::enable_if_t<not(std::is_same_v<std::remove_const_t<U>,
int[]>) && not(std::is_same_v<typename std::remove_const<U>::type, char[10]>),
bool> = true,
+ // CHECK-MESSAGES: :[[@LINE-1]]:73: warning: do not declare
C-style arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ // CHECK-MESSAGES: :[[@LINE-2]]:140: warning: do not declare
C-style arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ typename = typename std::remove_const<int[10]>::type,
+ // CHECK-MESSAGES: :[[@LINE-1]]:51: warning: do not declare
C-style arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ typename = std::remove_const_t<int[]>>
+ // CHECK-MESSAGES: :[[@LINE-1]]:44: warning: do not declare
C-style arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ class MyInnerClassTemplate {
+ public:
+ MyInnerClassTemplate(const U&) {}
+ private:
+ U field[3];
+ // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: do not declare C-style
arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ };
+
+ MyClassTemplate(const T&) {}
+
+ private:
+ T field[7];
+ // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+};
+
+// an explicit instantiation
+template
+class MyClassTemplate<int[2]>;
+// CHECK-MESSAGES: :[[@LINE-1]]:23: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+using MyArrayType = int[3];
+// CHECK-MESSAGES: :[[@LINE-1]]:21: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+// another explicit instantiation
+template
+class MyClassTemplate<MyArrayType>;
+// no diagnostic is expected here since no C-style array type got written here
+
+// within below template decl, no array type findings are expected within the
template parameter declarations since not a single C-style array type got
written explicitly
+template <typename T,
+ bool = std::is_same_v<T, int>,
+ bool = std::is_same<T, int>::value,
+ bool = std::is_same_v<std::remove_const_t<T>, int>,
+ bool = std::is_same<std::remove_const_t<T>, int>::value,
+ bool = std::is_same_v<typename std::remove_const<T>::type, int>,
+ bool = std::is_same<typename std::remove_const<T>::type, int>::value,
+ std::enable_if_t<not(std::is_same_v<std::remove_const_t<T>, int>) &&
not(std::is_same_v<typename std::remove_const<T>::type, char>), bool> = true,
+ typename std::enable_if<not(std::is_same_v<std::remove_const_t<T>,
int>) && not(std::is_same_v<typename std::remove_const<T>::type, char>),
bool>::type = true,
+ typename =
std::enable_if_t<not(std::is_same_v<std::remove_const_t<T>, int>) &&
not(std::is_same_v<typename std::remove_const<T>::type, char>)>,
+ typename = typename std::remove_const<T>::type,
+ typename = std::remove_const_t<T>>
+void func(const T& param) {
+ int array1[1];
+ // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+ T array2[2];
+ // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+ T value;
+}
+
+// here, however, plenty of array type findings are expected for below
template parameter declarations since C-style array types are written explicitly
+template <typename T = int[],
+ // CHECK-MESSAGES: :[[@LINE-1]]:24: warning: do not declare C-style
arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ bool = std::is_same_v<T, int[]>,
+ // CHECK-MESSAGES: :[[@LINE-1]]:36: warning: do not declare C-style
arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ bool = std::is_same<T, int[10]>::value,
+ // CHECK-MESSAGES: :[[@LINE-1]]:34: warning: do not declare C-style
arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ std::enable_if_t<not(std::is_same_v<std::remove_const_t<T>, int[]>)
&& not(std::is_same_v<typename std::remove_const<T>::type, char[10]>), bool> =
true,
+ // CHECK-MESSAGES: :[[@LINE-1]]:71: warning: do not declare C-style
arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ // CHECK-MESSAGES: :[[@LINE-2]]:138: warning: do not declare C-style
arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ typename = typename std::remove_const<int[10]>::type,
+ // CHECK-MESSAGES: :[[@LINE-1]]:49: warning: do not declare C-style
arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+ typename = std::remove_const_t<int[]>>
+ // CHECK-MESSAGES: :[[@LINE-1]]:42: warning: do not declare C-style
arrays, use 'std::array' instead [modernize-avoid-c-arrays]
+void fun(const T& param) {
+ int array3[3];
+ // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+ T array4[4];
+ // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+ T value;
+}
+
+template<typename T>
+T some_constant{};
+
+// explicit instantiations
+template
+int some_constant<int[5]>[5];
+// CHECK-MESSAGES: :[[@LINE-1]]:19: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+template
+int some_constant<decltype(ak)>[4];
+// no diagnostic is expected here since explicit instantiations aren't
represented as `TypeLoc` in the AST and we hence cannot match them as such
+
+MyArrayType mk;
+// no diagnostic is expected here since no C-style array type got written here
+
+// explicit specializations
+template<>
+int some_constant<int[7]>[7]{};
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: do not declare C-style arrays, use
'std::array' instead [modernize-avoid-c-arrays]
+// CHECK-MESSAGES: :[[@LINE-2]]:19: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+template<>
+int some_constant<decltype(mk)>[3]{};
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: do not declare C-style arrays, use
'std::array' instead [modernize-avoid-c-arrays]
+
+void testArrayInTemplateType() {
+ int t[10];
+ // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+ func(t);
+ fun(t);
+
+ func<decltype(t)>({});
+ fun<decltype(t)>({});
+
+ func<int[1]>({});
+ // CHECK-MESSAGES: :[[@LINE-1]]:8: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+ fun<int[1]>({});
+ // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+ MyClassTemplate var{t};
+ MyClassTemplate<decltype(t)> var1{{}};
+ MyClassTemplate<int[2]> var2{{}};
+ // CHECK-MESSAGES: :[[@LINE-1]]:19: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+ decltype(var1)::MyInnerClassTemplate var3{t};
+ decltype(var1)::MyInnerClassTemplate<decltype(t)> var4{{}};
+ decltype(var1)::MyInnerClassTemplate<char[5]> var5{{}};
+ // CHECK-MESSAGES: :[[@LINE-1]]:40: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+
+ MyClassTemplate<decltype(t)>::MyInnerClassTemplate var6{t};
+ MyClassTemplate<decltype(t)>::MyInnerClassTemplate<decltype(t)> var7{{}};
+ MyClassTemplate<decltype(t)>::MyInnerClassTemplate<char[8]> var8{{}};
+ // CHECK-MESSAGES: :[[@LINE-1]]:54: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+ MyClassTemplate<int[9]>::MyInnerClassTemplate<char[9]> var9{{}};
+ // CHECK-MESSAGES: :[[@LINE-1]]:19: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+ // CHECK-MESSAGES: :[[@LINE-2]]:49: warning: do not declare C-style arrays,
use 'std::array' instead [modernize-avoid-c-arrays]
+}
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