[clang-tools-extra] [clang-tidy] Avoid expensive AST traversal in RedundantTypenameCheck (PR #170540)

[Victor Chernyakin via cfe-commits]

================
@@ -18,9 +18,13 @@ using namespace clang::ast_matchers;
 namespace clang::tidy::readability {
 
 void RedundantTypenameCheck::registerMatchers(MatchFinder *Finder) {
-  Finder->addMatcher(typeLoc(unless(hasAncestor(decl(isInstantiated()))))
-                         .bind("nonDependentTypeLoc"),
-                     this);
+  Finder->addMatcher(
+      typeLoc(loc(TypeMatcher(anyOf(typedefType(), tagType(),
+                                    deducedTemplateSpecializationType(),
+                                    templateSpecializationType()))),
+              unless(hasAncestor(decl(isInstantiated()))))
+          .bind("nonDependentTypeLoc"),
+      this);
----------------
localspook wrote:

> It seems that we can remove unless(...). The traverse mode of this checker is TK_IgnoreUnlessSpelledInSource, so decl(isInstantiated()) doesn't matches anything IIUC.

I originally added the `unless` to make this test case pass:
https://github.com/llvm/llvm-project/blob/5911754a3085e1c95cec12971f075ab3f024d71d/clang-tools-extra/test/clang-tidy/checkers/readability/redundant-typename.cpp#L167-L170
Without the `unless`, it fails; the traversal seems to descend into the instantiation despite the traversal mode being `TK_IgnoreUnlessSpelledInSource`. Experimenting just now, I tried setting the traversal mode on the matcher explicitly:
```cpp
  Finder->addMatcher(traverse(TK_IgnoreUnlessSpelledInSource, typeLoc()
                         .bind("nonDependentTypeLoc")),
                     this);
```
And now it *does* work! Is there maybe an issue causing the traversal mode to not get propagated?

https://github.com/llvm/llvm-project/pull/170540