[clang-tools-extra] [clang-tidy] Disable bugprone-multi-level-pointer-conversion in C code (PR #141209)

[Carlos Galvez via cfe-commits]

https://github.com/carlosgalvezp updated https://github.com/llvm/llvm-project/pull/141209

>From 4de236aac2c75c1c092ac6b46591839678114365 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Carlos=20G=C3=A1lvez?= <carlos.galvez at zenseact.com>
Date: Fri, 23 May 2025 07:45:04 +0000
Subject: [PATCH] [clang-tidy] Add option to disable
 bugprone-multi-level-pointer-conversion in C code

Sometimes a project may want to enable this check only in C++, and
disable it in C, since the patterns the check warns about are quite
common and idiomatic in C, and there are no better alternatives.

Fixes #140659
---
 .../MultiLevelImplicitPointerConversionCheck.cpp      | 11 +++++++++++
 .../MultiLevelImplicitPointerConversionCheck.h        | 10 ++++++++--
 clang-tools-extra/docs/ReleaseNotes.rst               |  4 ++++
 .../multi-level-implicit-pointer-conversion.rst       |  9 +++++++++
 .../multi-level-implicit-pointer-conversion.c         | 11 +++++++++++
 5 files changed, 43 insertions(+), 2 deletions(-)
 create mode 100644 clang-tools-extra/test/clang-tidy/checkers/bugprone/multi-level-implicit-pointer-conversion.c

diff --git a/clang-tools-extra/clang-tidy/bugprone/MultiLevelImplicitPointerConversionCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/MultiLevelImplicitPointerConversionCheck.cpp
index 7a989b07119aa..1a23473fdd229 100644
--- a/clang-tools-extra/clang-tidy/bugprone/MultiLevelImplicitPointerConversionCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/MultiLevelImplicitPointerConversionCheck.cpp
@@ -57,6 +57,17 @@ AST_MATCHER(QualType, isPointerType) {
 
 } // namespace
 
+MultiLevelImplicitPointerConversionCheck::
+    MultiLevelImplicitPointerConversionCheck(StringRef Name,
+                                             ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context), EnableInC(Options.get("EnableInC", true)) {
+}
+
+void MultiLevelImplicitPointerConversionCheck::storeOptions(
+    ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "EnableInC", EnableInC);
+}
+
 void MultiLevelImplicitPointerConversionCheck::registerMatchers(
     MatchFinder *Finder) {
   Finder->addMatcher(
diff --git a/clang-tools-extra/clang-tidy/bugprone/MultiLevelImplicitPointerConversionCheck.h b/clang-tools-extra/clang-tidy/bugprone/MultiLevelImplicitPointerConversionCheck.h
index 13228145ff35f..ef5f9f103c893 100644
--- a/clang-tools-extra/clang-tidy/bugprone/MultiLevelImplicitPointerConversionCheck.h
+++ b/clang-tools-extra/clang-tidy/bugprone/MultiLevelImplicitPointerConversionCheck.h
@@ -21,11 +21,17 @@ namespace clang::tidy::bugprone {
 class MultiLevelImplicitPointerConversionCheck : public ClangTidyCheck {
 public:
   MultiLevelImplicitPointerConversionCheck(StringRef Name,
-                                           ClangTidyContext *Context)
-      : ClangTidyCheck(Name, Context) {}
+                                           ClangTidyContext *Context);
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
   void registerMatchers(ast_matchers::MatchFinder *Finder) override;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
   std::optional<TraversalKind> getCheckTraversalKind() const override;
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return EnableInC ? true : LangOpts.CPlusPlus;
+  }
+
+private:
+  bool const EnableInC;
 };
 
 } // namespace clang::tidy::bugprone
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index a275d2ccfa004..10f6cf670ae16 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -159,6 +159,10 @@ Changes in existing checks
   false positives on deleted constructors that cannot be used to construct
   objects, even if they have public or protected access.
 
+- Added an option to :doc:`bugprone-multi-level-implicit-pointer-conversion
+  <clang-tidy/checks/bugprone/multi-level-implicit-pointer-conversion>` to
+  choose whether to enable the check in C code or not.
+
 - Improved :doc:`bugprone-optional-value-conversion
   <clang-tidy/checks/bugprone/optional-value-conversion>` check to detect
   conversion in argument of ``std::make_optional``.
diff --git a/clang-tools-extra/docs/clang-tidy/checks/bugprone/multi-level-implicit-pointer-conversion.rst b/clang-tools-extra/docs/clang-tidy/checks/bugprone/multi-level-implicit-pointer-conversion.rst
index e6dc5c13aa025..0244687ac4e4b 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/bugprone/multi-level-implicit-pointer-conversion.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/bugprone/multi-level-implicit-pointer-conversion.rst
@@ -42,3 +42,12 @@ Additionally, it is recommended that developers thoroughly check and verify the
 safety of the conversion before using an explicit cast. This extra level of
 caution can help catch potential issues early on in the development process,
 improving the overall reliability and maintainability of the code.
+
+
+Options
+-------
+
+.. option:: EnableInC
+
+   If `true`, enables the check in C code (it is always enabled in C++ code).
+   Default is `true`.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/multi-level-implicit-pointer-conversion.c b/clang-tools-extra/test/clang-tidy/checkers/bugprone/multi-level-implicit-pointer-conversion.c
new file mode 100644
index 0000000000000..9dc5dae5c80f5
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/multi-level-implicit-pointer-conversion.c
@@ -0,0 +1,11 @@
+// RUN: %check_clang_tidy -check-suffixes=ENABLE-IN-C %s bugprone-multi-level-implicit-pointer-conversion %t -- -config="{CheckOptions: {bugprone-multi-level-implicit-pointer-conversion.EnableInC: true}}"
+// RUN: %check_clang_tidy -check-suffixes=DISABLE-IN-C %s bugprone-multi-level-implicit-pointer-conversion %t -- -config="{CheckOptions: {bugprone-multi-level-implicit-pointer-conversion.EnableInC: false}}"
+
+void free(void*);
+
+void test() {
+  char **p;
+  free(p);
+  // CHECK-MESSAGES-ENABLE-IN-C: :[[@LINE-1]]:8: warning: multilevel pointer conversion from 'char **' to 'void *', please use explicit cast [bugprone-multi-level-implicit-pointer-conversion]
+  free((void *)p);
+}