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[clang-tidy]suggest use std::span as replacement of c array in C++20 for modernize-avoid-c-arrays (#108555)
The incompleted C-Array in parameter does not own memory. Instead, It is equivalent to pointer. So we should not use `std::array` as recommended modern C++ replacement, but use `std::vector` and `std::span` in C++20
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8 files changed

+54
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‎clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp

+23-4
Original file line numberDiff line numberDiff line change
@@ -9,6 +9,7 @@
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#include "AvoidCArraysCheck.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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@@ -60,6 +61,7 @@ void AvoidCArraysCheck::registerMatchers(MatchFinder *Finder) {
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Finder->addMatcher(
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typeLoc(hasValidBeginLoc(), hasType(arrayType()),
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optionally(hasParent(parmVarDecl().bind("param_decl"))),
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unless(anyOf(hasParent(parmVarDecl(isArgvOfMain())),
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hasParent(varDecl(isExternC())),
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hasParent(fieldDecl(
@@ -72,11 +74,28 @@ void AvoidCArraysCheck::registerMatchers(MatchFinder *Finder) {
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void AvoidCArraysCheck::check(const MatchFinder::MatchResult &Result) {
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const auto *ArrayType = Result.Nodes.getNodeAs<TypeLoc>("typeloc");
75-
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const bool IsInParam =
78+
Result.Nodes.getNodeAs<ParmVarDecl>("param_decl") != nullptr;
79+
const bool IsVLA = ArrayType->getTypePtr()->isVariableArrayType();
80+
enum class RecommendType { Array, Vector, Span };
81+
llvm::SmallVector<const char *> RecommendTypes{};
82+
if (IsVLA) {
83+
RecommendTypes.push_back("std::vector<>");
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} else if (ArrayType->getTypePtr()->isIncompleteArrayType() && IsInParam) {
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// in function parameter, we also don't know the size of
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// IncompleteArrayType.
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if (Result.Context->getLangOpts().CPlusPlus20)
88+
RecommendTypes.push_back("std::span<>");
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else {
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RecommendTypes.push_back("std::array<>");
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RecommendTypes.push_back("std::vector<>");
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}
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} else {
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RecommendTypes.push_back("std::array<>");
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}
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diag(ArrayType->getBeginLoc(),
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"do not declare %select{C-style|C VLA}0 arrays, use "
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"%select{std::array<>|std::vector<>}0 instead")
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<< ArrayType->getTypePtr()->isVariableArrayType();
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"do not declare %select{C-style|C VLA}0 arrays, use %1 instead")
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<< IsVLA << llvm::join(RecommendTypes, " or ");
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}
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} // namespace clang::tidy::modernize

‎clang-tools-extra/docs/ReleaseNotes.rst

+5
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@@ -137,6 +137,11 @@ Changes in existing checks
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<clang-tidy/checks/misc/definitions-in-headers>` check by rewording the
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diagnostic note that suggests adding ``inline``.
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- Improved :doc:`modernize-avoid-c-arrays
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<clang-tidy/checks/modernize/avoid-c-arrays>` check to suggest using ``std::span``
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as a replacement for parameters of incomplete C array type in C++20 and
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``std::array`` or ``std::vector`` before C++20.
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- Improved :doc:`modernize-use-std-format
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<clang-tidy/checks/modernize/use-std-format>` check to support replacing
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member function calls too.

‎clang-tools-extra/docs/clang-tidy/checks/modernize/avoid-c-arrays.rst

+3
Original file line numberDiff line numberDiff line change
@@ -10,6 +10,9 @@ modernize-avoid-c-arrays
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Finds C-style array types and recommend to use ``std::array<>`` /
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``std::vector<>``. All types of C arrays are diagnosed.
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For incomplete C-style array types appeared in parameters, It would be better to
14+
use ``std::span`` / ``gsl::span`` as replacement.
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However, fix-it are potentially dangerous in header files and are therefore not
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emitted right now.
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‎clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays-c++20.cpp

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@@ -0,0 +1,11 @@
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// RUN: %check_clang_tidy -std=c++20 %s modernize-avoid-c-arrays %t
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int f1(int data[], int size) {
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// CHECK-MESSAGES: :[[@LINE-1]]:8: warning: do not declare C-style arrays, use std::span<> instead
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int f4[] = {1, 2};
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// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays, use std::array<> instead
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}
8+
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int f2(int data[100]) {
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// CHECK-MESSAGES: :[[@LINE-1]]:8: warning: do not declare C-style arrays, use std::array<> instead
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}

‎clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays-ignores-main.cpp

+3-3
Original file line numberDiff line numberDiff line change
@@ -1,7 +1,7 @@
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// RUN: %check_clang_tidy %s modernize-avoid-c-arrays %t
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// RUN: %check_clang_tidy -std=c++17 %s modernize-avoid-c-arrays %t
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int not_main(int argc, char *argv[]) {
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// CHECK-MESSAGES: :[[@LINE-1]]:24: warning: do not declare C-style arrays, use std::array<> instead
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// CHECK-MESSAGES: :[[@LINE-1]]:24: warning: do not declare C-style arrays, use std::array<> or std::vector<> instead
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int f4[] = {1, 2};
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// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays, use std::array<> instead
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}
@@ -11,7 +11,7 @@ int main(int argc, char *argv[]) {
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// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays, use std::array<> instead
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auto not_main = [](int argc, char *argv[]) {
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// CHECK-MESSAGES: :[[@LINE-1]]:32: warning: do not declare C-style arrays, use std::array<> instead
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// CHECK-MESSAGES: :[[@LINE-1]]:32: warning: do not declare C-style arrays, use std::array<> or std::vector<> instead
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int f6[] = {1, 2};
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// CHECK-MESSAGES: :[[@LINE-1]]:5: warning: do not declare C-style arrays, use std::array<> instead
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};

‎clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays-ignores-strings.cpp

+2-2
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@@ -1,9 +1,9 @@
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// RUN: %check_clang_tidy %s modernize-avoid-c-arrays %t -- \
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// RUN: %check_clang_tidy -std=c++17 %s modernize-avoid-c-arrays %t -- \
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// RUN: -config='{CheckOptions: { modernize-avoid-c-arrays.AllowStringArrays: true }}'
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const char name[] = "name";
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const char array[] = {'n', 'a', 'm', 'e', '\0'};
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// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: do not declare C-style arrays, use std::array<> instead [modernize-avoid-c-arrays]
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void takeCharArray(const char name[]);
9-
// CHECK-MESSAGES: :[[@LINE-1]]:26: warning: do not declare C-style arrays, use std::array<> instead [modernize-avoid-c-arrays]
9+
// CHECK-MESSAGES: :[[@LINE-1]]:26: warning: do not declare C-style arrays, use std::array<> or std::vector<> instead [modernize-avoid-c-arrays]

‎clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays-ignores-three-arg-main.cpp

+5-5
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@@ -1,8 +1,8 @@
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// RUN: %check_clang_tidy %s modernize-avoid-c-arrays %t
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// RUN: %check_clang_tidy -std=c++17 %s modernize-avoid-c-arrays %t
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int not_main(int argc, char *argv[], char *argw[]) {
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// CHECK-MESSAGES: :[[@LINE-1]]:24: warning: do not declare C-style arrays, use std::array<> instead
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// CHECK-MESSAGES: :[[@LINE-2]]:38: warning: do not declare C-style arrays, use std::array<> instead
4+
// CHECK-MESSAGES: :[[@LINE-1]]:24: warning: do not declare C-style arrays, use std::array<> or std::vector<> instead
5+
// CHECK-MESSAGES: :[[@LINE-2]]:38: warning: do not declare C-style arrays, use std::array<> or std::vector<> instead
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int f4[] = {1, 2};
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// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays, use std::array<> instead
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}
@@ -12,8 +12,8 @@ int main(int argc, char *argv[], char *argw[]) {
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// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays, use std::array<> instead
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auto not_main = [](int argc, char *argv[], char *argw[]) {
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// CHECK-MESSAGES: :[[@LINE-1]]:32: warning: do not declare C-style arrays, use std::array<> instead
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// CHECK-MESSAGES: :[[@LINE-2]]:46: warning: do not declare C-style arrays, use std::array<> instead
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// CHECK-MESSAGES: :[[@LINE-1]]:32: warning: do not declare C-style arrays, use std::array<> or std::vector<> instead
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// CHECK-MESSAGES: :[[@LINE-2]]:46: warning: do not declare C-style arrays, use std::array<> or std::vector<> instead
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int f6[] = {1, 2};
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// CHECK-MESSAGES: :[[@LINE-1]]:5: warning: do not declare C-style arrays, use std::array<> instead
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};

‎clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays.cpp

+2-2
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@@ -1,4 +1,4 @@
1-
// RUN: %check_clang_tidy %s modernize-avoid-c-arrays %t
1+
// RUN: %check_clang_tidy -std=c++17 %s modernize-avoid-c-arrays %t
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int a[] = {1, 2};
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// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: do not declare C-style arrays, use std::array<> instead
@@ -91,4 +91,4 @@ const char name[] = "Some string";
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// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: do not declare C-style arrays, use std::array<> instead [modernize-avoid-c-arrays]
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void takeCharArray(const char name[]);
94-
// CHECK-MESSAGES: :[[@LINE-1]]:26: warning: do not declare C-style arrays, use std::array<> instead [modernize-avoid-c-arrays]
94+
// CHECK-MESSAGES: :[[@LINE-1]]:26: warning: do not declare C-style arrays, use std::array<> or std::vector<> instead [modernize-avoid-c-arrays]

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