[clang] [clang-tools-extra] [clang-tidy] Add new check: `readability-redundant-typename` (PR #161574)

[Victor Chernyakin via cfe-commits]

================
@@ -0,0 +1,68 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "RedundantTypenameCheck.h"
+#include "clang/AST/TypeLoc.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Basic/Diagnostic.h"
+#include "clang/Sema/DeclSpec.h"
+
+using namespace clang::ast_matchers;
+using namespace clang::ast_matchers::internal;
+
+namespace clang::tidy::readability {
+
+void RedundantTypenameCheck::registerMatchers(MatchFinder *Finder) {
+  // NOLINTNEXTLINE(readability-identifier-naming)
+  const VariadicDynCastAllOfMatcher<TypeLoc, TypedefTypeLoc> typedefTypeLoc;
+  Finder->addMatcher(typedefTypeLoc().bind("typedefTypeLoc"), this);
+
+  if (!getLangOpts().CPlusPlus20)
+    return;
+
+  // NOLINTBEGIN(readability-identifier-naming)
+  const VariadicDynCastAllOfMatcher<Stmt, CXXNamedCastExpr> cxxNamedCastExpr;
+  const auto inImplicitTypenameContext = anyOf(
----------------
localspook wrote:

That doesn't work as well as we might like, because some of those inner matchers match on expressions, and others on declarations, so you can't pass them all to one `anyOf()`. It's still possible to reduce duplication, but it needs to look like:
```cpp
anyOf(
	hasParent(decl(anyOf(...))),
	hasParent(expr(anyOf(...)))
)
```
I pushed a commit that does that. Honestly don't know which version I prefer, so I'll leave it to others to decide if it's an improvement.

https://github.com/llvm/llvm-project/pull/161574