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

[Yanzuo Liu via cfe-commits]

================
@@ -0,0 +1,163 @@
+//===--- UseToUnderlyingCheck.cpp - clang-tidy ----------------------------===//
+//
+// 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 "UseToUnderlyingCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy {
+
+template <>
+struct OptionEnumMapping<modernize::UseToUnderlyingCheck::ImpreciseCastsKind> {
+  static llvm::ArrayRef<
+      std::pair<modernize::UseToUnderlyingCheck::ImpreciseCastsKind, StringRef>>
+  getEnumMapping() {
+    using ImpreciseCastsKind =
+        modernize::UseToUnderlyingCheck::ImpreciseCastsKind;
+    static constexpr std::pair<ImpreciseCastsKind, StringRef> Mapping[] = {
+        {ImpreciseCastsKind::Ignore, "Ignore"},
+        {ImpreciseCastsKind::Warn, "Warn"},
+        {ImpreciseCastsKind::PreserveType, "PreserveType"},
+        {ImpreciseCastsKind::UseUnderlyingType, "UseUnderlyingType"},
+    };
+    return {Mapping};
+  }
+};
+
+} // namespace clang::tidy
+
+namespace clang::tidy::modernize {
+
+UseToUnderlyingCheck::UseToUnderlyingCheck(StringRef Name,
+                                           ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      ImpreciseCasts(Options.get("ImpreciseCasts", ImpreciseCastsKind::Warn)),
+      ReplacementFunction(
+          Options.get("ReplacementFunction", "std::to_underlying")),
+      IncludeInserter(Options.getLocalOrGlobal("IncludeStyle",
+                                               utils::IncludeSorter::IS_LLVM),
+                      areDiagsSelfContained()),
+      MaybeHeaderToInclude(Options.get("ReplacementFunctionHeader")) {
+  if (!MaybeHeaderToInclude && ReplacementFunction == "std::to_underlying")
----------------
zwuis wrote:

We can warn when the replacement function is `std::to_underlying` but the header is not `<utility>`.

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