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

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@@ -0,0 +1,45 @@
+//===--- 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);
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+
+private:
+  const bool StrictMode;
+  const bool EnableCountingEnumHeuristic;
+  const StringRef RawCountingEnumPrefixes;
+  const StringRef RawCountingEnumSuffixes;
+  std::vector<StringRef> ParsedCountingEnumPrefixes;
+  std::vector<StringRef> ParsedCountingEnumSuffixes;
+  const bool CountingEnumPrefixesSet;
+  const bool CountingEnumSuffixesSet;
+  EnumConstantDecl *CountingEnumConstantDecl;
----------------
whisperity wrote:

Clang-Tidy checks usually consume the AST but do not modify it, so pointing to a non-`const` node here is definitely suspicious.

```suggestion
  const EnumConstantDecl *CountingEnumConstantDecl;
```

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