I wrote:
> Now that I've looked this over I'm starting to feel uncomfortable
> again, because we can't actually be quite sure about how the remote
> parser's heuristic will act.
Actually ... we could make that a lot safer by insisting that the
other input be a plain Var, which'd necessarily be a column of the
foreign table. That would still cover most cases of practical
interest, I think, and it would remove any question of whether
implicit coercions had snuck in. It's more restrictive than I'd
really like, but I think it's less likely to cause problems.
regards, tom lane