[clang-tools-extra] Add check 'modernize-use-enum-class' (PR #138282)

[Baranov Victor via cfe-commits]

================
@@ -0,0 +1,34 @@
+//===--- UseEnumClassCheck.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 "UseEnumClassCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::modernize {
+
+void UseEnumClassCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      traverse(TK_AsIs,
+               enumDecl(unless(isScoped()), unless(hasParent(recordDecl()))))
----------------
vbvictor wrote:

```suggestion
               enumDecl(unless(isScoped())
```
If we strictly follow CppCoreGuidelines (which we should do it `cppcoreguidelines-` checks), there are no mention of "established pattern to limit the scope".
So I think we need to remove this condition or at least create an option like `IgnoreInClasses` to optionally relax this check.

https://github.com/llvm/llvm-project/pull/138282