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

>
>
> It seems that ON_ERROR_STOP is mostly ignored by design when in
> interactive mode, probably because it is nicer not to disconnect the user
> who is actually typing things on a terminal.
>
> """
>   ON_ERROR_STOP
>
> By default, command processing continues after an error. When this
> variable is set to on, processing will instead stop immediately. In
> interactive mode, psql will return to the command prompt; otherwise, psql
> will exit, returning error code 3 to distinguish this case from fatal error
> conditions, which are reported using error code 1.
> """
>

This was my previous understanding of ON_ERROR_STOP. Somewhere in the
course of developing this patch I lost that. Glad to have it back.

The only changes I made were to invalid booleans on if/elif, and the final
branch balancing check won't set status to EXIT_USER unless it's
non-interactive and ON_ERROR_STOP = on.

> \if true
new \if is true, executing commands
> \endif
exited \if, executing commands
> \if false
new \if is false, ignoring commands until next \elif, \else, or \endif
> \endif
exited \if, executing commands
> \if error
unrecognized value "error" for "\if <expr>": boolean expected
new \if is invalid, ignoring commands until next \endif
> \echo foo
inside inactive branch, command ignored.
> ^C
escaped \if, executing commands
> \echo foo
foo
> \endif
encountered un-matched \endif
>