[clang-tools-extra] [clang-tidy] Add new check bugprone-tagged-union-member-count (PR #89925)

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=?utf-8?b?R8OhYm9yIFTDs3RodsOhcmk=?= <tigbrcode at protonmail.com>,
=?utf-8?b?R8OhYm9yIFTDs3RodsOhcmk=?= <tigbrcode at protonmail.com>
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In-Reply-To: <llvm.org/llvm/llvm-project/pull/89925 at github.com>


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@@ -0,0 +1,31 @@
+//===--- TaggedUnionMemberCountCheck.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_TAGGEDUNIONMEMBERCOUNTCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_TAGGEDUNIONMEMBERCOUNTCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::bugprone {
+
+// Gives warnings for tagged unions, where the number of tags is
+// different from the number of data members inside the union.
+//
+// For the user-facing documentation see:
+// http://clang.llvm.org/extra/clang-tidy/checks/bugprone/tagged-union-member-count.html
+class TaggedUnionMemberCountCheck : public ClangTidyCheck {
+public:
+  TaggedUnionMemberCountCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
----------------
tigbr wrote:

This option looks interesting, however it breaks some of the intended matches, for example [the test case in C++ when the union field is anonymous](https://github.com/tigbr/llvm-project/blob/be3ec1a4e9ac3309da8f2037334de68bd478883f/clang-tools-extra/test/clang-tidy/checkers/bugprone/tagged-union-member-count.cpp#L176).

https://github.com/llvm/llvm-project/pull/89925