Andrey Lepikhov <a.lepikhov@postgrespro.ru> writes:
> It is possible that custom_scan_tlist is designed too nontrivially, and
> it is possible that it needs some comments describing in more detail how
> to use it.
I totally buy the argument that the custom scan stuff is
underdocumented :-(.
FWIW, if we did have a use-case showing that somebody would like to make
custom scans that can't project, the way to do it would be to add a flag
bit showing whether a particular CustomPath/CustomScan could project or
not. Not to assume that they all can't. This wouldn't be that much code
really, but I'd still like to see a plausible use-case before adding it,
because it'd be a small API break for existing CustomPath providers.
regards, tom lane