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

[Dave Lee via cfe-commits]

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@@ -0,0 +1,202 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "FormatvStringCheck.h"
+#include "clang/AST/Expr.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallBitVector.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Error.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::llvm_check {
+
+namespace {
+
+struct ParseResult {
+  llvm::SmallVector<unsigned, 4> Indices;
+  unsigned MaxIndex = 0;
+};
+
+} // namespace
+
+static llvm::Expected<ParseResult> parseFormatvString(llvm::StringRef Fmt) {
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kastiglione wrote:

I misunderstood, yes some of this validation could be reused for `std::format`

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