[clang-tools-extra] [clang-tidy] Add `llvm-formatv-string` (PR #195974)

[Victor Chernyakin via cfe-commits]

================
@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_LLVM_FORMATVSTRINGCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_LLVM_FORMATVSTRINGCHECK_H
+
+#include "../ClangTidyCheck.h"
+#include "llvm/ADT/StringSet.h"
+
+namespace clang::tidy::llvm_check {
+
+/// Validates llvm::formatv format strings against the provided arguments.
+///
+/// Checks that:
+/// - The number of format indices matches the number of arguments.
+/// - Every argument is used by the format string.
+/// - Automatic and explicit indices are not mixed.
+///
+/// For the user-facing documentation see:
+/// https://clang.llvm.org/extra/clang-tidy/checks/llvm/formatv-string.html
+class FormatvStringCheck : public ClangTidyCheck {
+public:
+  FormatvStringCheck(StringRef Name, ClangTidyContext *Context);
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus;
+  }
+  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 {
+    return TK_IgnoreUnlessSpelledInSource;
+  }
+
+private:
+  llvm::StringSet<> Functions;
+  const std::string AdditionalFunctions;
----------------
localspook wrote:

```suggestion
  const StringRef AdditionalFunctions;
```

https://github.com/llvm/llvm-project/pull/195974