[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

1 files changed, 23 insertions, 4 deletions

diff --git a/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp b/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp
index 89790ea..9877819 100644
--- a/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp
@@ -9,6 +9,7 @@
 #include "AvoidCArraysCheck.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
 
 using namespace clang::ast_matchers;
 
@@ -60,6 +61,7 @@ void AvoidCArraysCheck::registerMatchers(MatchFinder *Finder) {
 
   Finder->addMatcher(
       typeLoc(hasValidBeginLoc(), hasType(arrayType()),
+              optionally(hasParent(parmVarDecl().bind("param_decl"))),
               unless(anyOf(hasParent(parmVarDecl(isArgvOfMain())),
                            hasParent(varDecl(isExternC())),
                            hasParent(fieldDecl(
@@ -72,11 +74,28 @@ void AvoidCArraysCheck::registerMatchers(MatchFinder *Finder) {
 
 void AvoidCArraysCheck::check(const MatchFinder::MatchResult &Result) {
   const auto *ArrayType = Result.Nodes.getNodeAs<TypeLoc>("typeloc");
-
+  const bool IsInParam =
+      Result.Nodes.getNodeAs<ParmVarDecl>("param_decl") != nullptr;
+  const bool IsVLA = ArrayType->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) {
+    // in function parameter, we also don't know the size of
+    // IncompleteArrayType.
+    if (Result.Context->getLangOpts().CPlusPlus20)
+      RecommendTypes.push_back("std::span<>");
+    else {
+      RecommendTypes.push_back("std::array<>");
+      RecommendTypes.push_back("std::vector<>");
+    }
+  } else {
+    RecommendTypes.push_back("std::array<>");
+  }
   diag(ArrayType->getBeginLoc(),
-       "do not declare %select{C-style|C VLA}0 arrays, use "
-       "%select{std::array<>|std::vector<>}0 instead")
-      << ArrayType->getTypePtr()->isVariableArrayType();
+       "do not declare %select{C-style|C VLA}0 arrays, use %1 instead")
+      << IsVLA << llvm::join(RecommendTypes, " or ");
 }
 
 } // namespace clang::tidy::modernize