[clang-tools-extra] [clang-tidy] Add redundant qualified alias check (PR #180404)

[Yanzuo Liu via cfe-commits]

================
@@ -0,0 +1,270 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "RedundantQualifiedAliasCheck.h"
+#include "../utils/LexerUtils.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/TypeLoc.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Basic/SourceManager.h"
+#include "clang/Lex/Lexer.h"
+#include <optional>
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::readability {
+
+namespace {
+
+struct NominalTypeLocInfo {
+  TypeLoc Loc;
+  bool HasQualifier = false;
+};
+
+struct EqualTokenInfo {
+  SourceLocation AfterEqualLoc;
+  bool SawComment = false;
+};
+
+} // namespace
+
+static bool hasMacroInRange(SourceRange Range, const SourceManager &SM,
+                            const LangOptions &LangOpts) {
+  if (Range.isInvalid())
+    return true;
+  return utils::lexer::rangeContainsExpansionsOrDirectives(Range, SM, LangOpts);
+}
+
+static std::optional<NominalTypeLocInfo> peelToNominalTypeLoc(TypeLoc TL) {
+  while (!TL.isNull()) {
+    if (const auto ParenTL = TL.getAs<ParenTypeLoc>()) {
+      TL = ParenTL.getInnerLoc();
+      continue;
+    }
+    if (const auto AttrTL = TL.getAs<AttributedTypeLoc>()) {
+      // Preserve any attributes by rewriting only the alias name and '='.
+      TL = AttrTL.getModifiedLoc();
+      continue;
+    }
+
+    if (const auto TypedefTL = TL.getAs<TypedefTypeLoc>()) {
+      // Avoid rewriting aliases that use an elaborated keyword
----------------
zwuis wrote:

Perhaps not in this PR, but it would be nice to support

```diff
-using Type = typename NS::Type;
+using typename NS::Type;
```

https://github.com/llvm/llvm-project/pull/180404