alt Hacker NewsI make no claim as to whether the change makes sense given that I didn't look at the callers of this function, but Result<bool> is an entirely reasonable pattern in Rust. If you want the callers to be able to distinguish between "has the subclass", "doesn't have the subclass", and "something went wrong" this is idiomatic Rust.
I wrongly guessed that the boolean in the original C code was for error handling when I skimmed it, but instead it is just a result value, while elog() and related macros/functions are used for general error handling in the C version. I agree that it makes sense in Rust and other languages with tagged unions.
Though often when applicable, a simple tagged union is used instead when that would document the intention better. Like, the Rust version of search_pg_class_full_form::call() returns a Some for cache hit and None for cache miss as far as I can skim, and that group of methods returning that could arguably have returned a basic enum instead with CacheHit(value) and CacheMiss. Though this is a nitpick on my part.