This feature was only used in two places, but contributed a non-trivial
amount to the complexity of RecursiveASTVisitor, and was buggy (see my
recent patches where I was fixing the bugs that I noticed). I don't
think the convenience benefit of this feature is worth the complexity.
Besides complexity, another issue with the current state of RecursiveASTVisitor is the non-uniformity in how it handles different AST nodes. All AST nodes follow a regular pattern, but operators are special -- and this special behavior not documented. Correct usage of RecursiveASTVisitor relies on shadowing member functions with specific names and signatures. Near misses don't cause any compile-time errors, incorrectly named or typed methods are just silently ignored. Therefore, predictability of RecursiveASTVisitor API is quite important.
This change reduces the size of the clang binary by 38 KB (0.2%) in
release mode, and by 7 MB (0.3%) in debug mode. The clang-tidy binary
is reduced by 205 KB (0.3%) in release mode, and by 5 MB (0.4%) in debug
mode. I don't think these code size improvements are significant enough
to justify this change on its own (for me, the primary motivation is
reducing code complexity), but they I think are a nice side-effect.