Why not use "http" site:docs.rs
? Or the rust docs bang? Or make a custom one?
I feel like this is not a bug/problem, as the "pin" setting is not meant to be a filter along the lines of "only this". It is supposed to show the one resource right on top, if applicable. E.g., when searching for "fish" and having wiki pinned, I do not want results solely from wikipedia.
This is what a bang or site filter with site:
is for. (IMO)