[clang] [clang-tidy] warn when `true` is used as a preprocessor keyword in C (PR #128265)

[via cfe-commits]

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@@ -0,0 +1,38 @@
+//===--- TrueMacroCheck.h - clang-tidy --------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_TRUEMACROCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_TRUEMACROCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::bugprone {
+
+/// In C++, `true` is considered a keyword by the preprocessor so an `#if
+/// true` enters the true branch, while in C, `true` is not treated as a
+/// special keyword by the preprocessor, so the false branch is entered.
+///
+/// The check identifies such cases, when `true` is used without being
+/// defined first and also offers fix-its in some cases.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/bugprone/true-macro.html
+class TrueMacroCheck : public ClangTidyCheck {
+public:
+  TrueMacroCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerPPCallbacks(const SourceManager &SM, Preprocessor *PP,
+                           Preprocessor *ModuleExpanderPP) override;
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.C99 || LangOpts.C11 || LangOpts.C17;
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isuckatcs wrote:

It is tested in the new clang diagnostic test.

https://github.com/llvm/llvm-project/pull/128265