[clang] [clang] Dispatch default overloads of `TemplateArgumentVisitor` to the implementation (PR #115336)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Egor Zhdan (egorzhdan)

<details>
<summary>Changes</summary>

This fixes an issue where overriding `clang::ConstTemplateArgumentVisitor::VisitTemplateArgument` in an implementation visitor class did not have the desired effect: the overload was not invoked when one of the visitor methods (e.g. `VisitDeclarationArgument`) is not implemented, instead it dispatched to `clang::ConstTemplateArgumentVisitor::VisitTemplateArgument` itself and always returned a default-initialized result.

This makes `TemplateArgumentVisitor` and `ConstTemplateArgumentVisitor` follow the implicit convention that is followed elsewhere in Clang AST, in `RecursiveASTVisitor` and `TypeVisitor`.

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Full diff: https://github.com/llvm/llvm-project/pull/115336.diff


1 Files Affected:

- (modified) clang/include/clang/AST/TemplateArgumentVisitor.h (+2-1) 


``````````diff
diff --git a/clang/include/clang/AST/TemplateArgumentVisitor.h b/clang/include/clang/AST/TemplateArgumentVisitor.h
index cf0d3220158063..923f045a995703 100644
--- a/clang/include/clang/AST/TemplateArgumentVisitor.h
+++ b/clang/include/clang/AST/TemplateArgumentVisitor.h
@@ -52,7 +52,8 @@ class Base {
 #define VISIT_METHOD(CATEGORY)                                                 \
   RetTy Visit##CATEGORY##TemplateArgument(REF(TemplateArgument) TA,            \
                                           ParamTys... P) {                     \
-    return VisitTemplateArgument(TA, std::forward<ParamTys>(P)...);            \
+    return static_cast<ImplClass *>(this)->VisitTemplateArgument(              \
+        TA, std::forward<ParamTys>(P)...);                                     \
   }
 
   VISIT_METHOD(Null);

``````````

</details>


https://github.com/llvm/llvm-project/pull/115336