[clang-tidy] Add AllowStringArrays option to modernize-avoid-c-arrays

[PiotrZSL]

Add AllowStringArrays option, enabling the exclusion of array types with deduced sizes constructed from string literals. This includes only var declarations of array of characters constructed directly from c-strings.

Closes #59475

[llvmbot]

@llvm/pr-subscribers-clang-tools-extra

@llvm/pr-subscribers-clang-tidy

Author: Piotr Zegar (PiotrZSL)

Changes

Add AllowStringArrays option, enabling the exclusion of array types with deduced sizes constructed from string literals. This includes only var declarations of array of characters constructed directly from c-strings.

Closes #59475

---

Full diff: https://github.com/llvm/llvm-project/pull/71701.diff

6 Files Affected:

• (modified) clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp (+19-2)
• (modified) clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.h (+10-4)
• (modified) clang-tools-extra/docs/ReleaseNotes.rst (+5)
• (modified) clang-tools-extra/docs/clang-tidy/checks/modernize/avoid-c-arrays.rst (+9)
• (added) clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays-ignores-strings.cpp (+6)
• (modified) clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays.cpp (+3)

diff --git a/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp b/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp
index d1b15479ffe7a93..ab1cdd62aa2cc01 100644
--- a/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.cpp
@@ -12,6 +12,8 @@
 
 using namespace clang::ast_matchers;
 
+namespace clang::tidy::modernize {
+
 namespace {
 
 AST_MATCHER(clang::TypeLoc, hasValidBeginLoc) {
@@ -38,16 +40,31 @@ AST_MATCHER(clang::ParmVarDecl, isArgvOfMain) {
 
 } // namespace
 
-namespace clang::tidy::modernize {
+AvoidCArraysCheck::AvoidCArraysCheck(StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      AllowStringArrays(Options.get("AllowStringArrays", false)) {}
+
+void AvoidCArraysCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "AllowStringArrays", AllowStringArrays);
+}
 
 void AvoidCArraysCheck::registerMatchers(MatchFinder *Finder) {
+  ast_matchers::internal::Matcher<TypeLoc> IgnoreStringArrayIfNeededMatcher =
+      anything();
+  if (AllowStringArrays)
+    IgnoreStringArrayIfNeededMatcher =
+        unless(typeLoc(loc(hasCanonicalType(incompleteArrayType(
+                           hasElementType(isAnyCharacter())))),
+                       hasParent(varDecl(hasInitializer(stringLiteral())))));
+
   Finder->addMatcher(
       typeLoc(hasValidBeginLoc(), hasType(arrayType()),
               unless(anyOf(hasParent(parmVarDecl(isArgvOfMain())),
                            hasParent(varDecl(isExternC())),
                            hasParent(fieldDecl(
                                hasParent(recordDecl(isExternCContext())))),
-                           hasAncestor(functionDecl(isExternC())))))
+                           hasAncestor(functionDecl(isExternC())))),
+              std::move(IgnoreStringArrayIfNeededMatcher))
           .bind("typeloc"),
       this);
 }
diff --git a/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.h b/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.h
index 7099f99c869498f..719e88e4b31662f 100644
--- a/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.h
+++ b/clang-tools-extra/clang-tidy/modernize/AvoidCArraysCheck.h
@@ -19,13 +19,19 @@ namespace clang::tidy::modernize {
 /// http://clang.llvm.org/extra/clang-tidy/checks/modernize/avoid-c-arrays.html
 class AvoidCArraysCheck : public ClangTidyCheck {
 public:
-  AvoidCArraysCheck(StringRef Name, ClangTidyContext *Context)
-      : ClangTidyCheck(Name, Context) {}
+  AvoidCArraysCheck(StringRef Name, ClangTidyContext *Context);
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
   bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
     return LangOpts.CPlusPlus11;
   }
-  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
-  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  std::optional<TraversalKind> getCheckTraversalKind() const override {
+    return TK_IgnoreUnlessSpelledInSource;
+  }
+
+private:
+  const bool AllowStringArrays;
 };
 
 } // namespace clang::tidy::modernize
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index fe8c7175d554c7b..97e532abbf8c715 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -330,6 +330,11 @@ Changes in existing checks
   <clang-tidy/checks/modernize/avoid-bind>` check to
   not emit a ``return`` for fixes when the function returns ``void``.
 
+- Improved :doc:`modernize-avoid-c-arrays
+  <clang-tidy/checks/modernize/avoid-c-arrays>` check by introducing the new
+  `AllowStringArrays` option, enabling the exclusion of array types with deduced
+  sizes constructed from string literals.
+
 - Improved :doc:`modernize-loop-convert
   <clang-tidy/checks/modernize/loop-convert>` to support for-loops with
   iterators initialized by free functions like ``begin``, ``end``, or ``size``
diff --git a/clang-tools-extra/docs/clang-tidy/checks/modernize/avoid-c-arrays.rst b/clang-tools-extra/docs/clang-tidy/checks/modernize/avoid-c-arrays.rst
index bc61033ff1fa1fa..acc628d58f80ee0 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/modernize/avoid-c-arrays.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/modernize/avoid-c-arrays.rst
@@ -58,3 +58,12 @@ such headers between C code, and C++ code.
 Similarly, the ``main()`` function is ignored. Its second and third parameters
 can be either ``char* argv[]`` or ``char** argv``, but cannot be
 ``std::array<>``.
+
+.. option:: AllowStringArrays
+
+  When set to `true` (default is `false`), incomplete array types constructed
+  from string literals will be ignored. Example:
+
+  .. code:: c++
+
+    const char name[] = "Some name";
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
new file mode 100644
index 000000000000000..545429b2be807e9
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-arrays-ignores-strings.cpp
@@ -0,0 +1,6 @@
+// RUN: %check_clang_tidy %s modernize-avoid-c-arrays %t -- \
+// RUN:  -config='{CheckOptions: { modernize-avoid-c-arrays.AllowStringArrays: true }}'
+
+const char name[] = "name";
+const char array[] = {'n', 'a', 'm', 'e', '\0'};
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: do not declare C-style arrays, use std::array<> instead [modernize-avoid-c-arrays]
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 dd3078010eb3805..4233f69337898ee 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
@@ -86,3 +86,6 @@ struct Bar {
   int j[1];
 };
 }
+
+const char name[] = "Some string";
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: do not declare C-style arrays, use std::array<> instead [modernize-avoid-c-arrays]

[5chmidti]

LGTM, but I'd prefer a second person to approve as well.

[HerrCai0907]

I may not work for

void f(const char name[]);

f("111");

[PiotrZSL]

I may not work for

void f(const char name[]);

f("111");

It should not work, as this is not array, but pointer. If you do sizeof(name) you get size of pointer, instead of number of elements in array.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[HerrCai0907]

It should not work, as this is not array, but pointer

Agree. But it fulfills the description of this opinion, since it looks like to construct a array from string literals.
It would be better to explain it in document.

incomplete array types constructed from string literals will be ignored.