Re: \if, \elseif, \else, \endif (was Re: [HACKERS] PSQL commands: \quit_if, \quit_unless)

Robert Haas <robertmhaas@gmail.com> writes:
> I (still) think this is a bad design.  Even if you've got all the
> messages just right as things stand today, some new feature that comes
> along in the future can change things so that they're not right any
> more, and nobody's going to relish maintaining this.

FWIW, I tend to agree that this is way overboard in terms of the amount of
complexity going into the messages.  Also, I do not like what seems to
be happening here:

>> $ psql test < test2.sql -v ON_ERROR_STOP=0
>> unrecognized value "error" for "\if <expr>": boolean expected
>> new \if is invalid, ignoring commands until next \endif

IMO, an erroneous backslash command should have no effect, period.
"It failed but we'll treat it as if it were valid" is a rathole
I don't want to descend into.  It's particularly bad in interactive
mode, because the most natural thing to do is correct your spelling
and issue the command again --- but if psql already decided to do
something on the strength of the mistaken command, that doesn't work,
and you'll have to do something or other to unwind the unwanted
control state before you can get back to what you meant to do.
        regards, tom lane