[clang-tools-extra] [clang-tidy] Add modernize-use-to-underlying check (PR #210459)

[Yanzuo Liu via cfe-commits]

================
@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_MODERNIZE_USETOUNDERLYINGCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USETOUNDERLYINGCHECK_H
+
+#include "../ClangTidyCheck.h"
+#include "../utils/IncludeInserter.h"
+#include <optional>
+
+namespace clang::tidy::modernize {
+
+/// Finds casts from a scoped enumeration to its underlying integer type and
+/// replaces them with a call to ``std::to_underlying`` (C++23).
+///
+/// For the user-facing documentation see:
+/// https://clang.llvm.org/extra/clang-tidy/checks/modernize/use-to-underlying.html
+class UseToUnderlyingCheck : public ClangTidyCheck {
+public:
+  /// How to treat an imprecise cast, i.e. a cast whose destination type is an
+  /// integer type other than the enumeration's underlying type.
+  enum class ImpreciseCastsKind {
+    /// Do not diagnose imprecise casts.
+    Ignore,
+    /// Diagnose imprecise casts but do not offer a fix-it.
+    Warn,
+    /// Wrap the operand in a call to the replacement function, preserving the
+    /// original destination type.
+    PreserveType,
+    /// Replace the whole cast with a call to the replacement function, changing
+    /// the resulting type to the underlying type.
+    UseUnderlyingType,
+  };
+
+  UseToUnderlyingCheck(StringRef Name, ClangTidyContext *Context);
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override;
+  void registerPPCallbacks(const SourceManager &SM, Preprocessor *PP,
+                           Preprocessor *ModuleExpanderPP) override;
+  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:
+  const ImpreciseCastsKind ImpreciseCasts;
+  const StringRef ReplacementFunction;
+  utils::IncludeInserter IncludeInserter;
+  std::optional<StringRef> MaybeHeaderToInclude;
----------------
zwuis wrote:

Can we use empty `StringRef` to indicate not prividing `#include` in fixit?

https://github.com/llvm/llvm-project/pull/210459