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

Hello Corey,

>> The check I was suggesting on whether Ctrl+C has been pressed
>>> on an empty line seems harder to implement, because get_interactive()
>>> just calls readline() or fgets(), which block to return when a whole
>>> line is ready. AFAICS psql can't know what was the edit-in-progress
>>> when these functions are interrupted by a signal instead of
>>> returning normally.
>>> But I don't think this check is essential, it could be left to another
>>> patch.
>>
>> Glad I wasn't missing something obvious.
>> I suppose we could base the behavior on whether there's at least one full
>> line already buffered.
>> However, I agree that it can be left to another patch.

Hmmm. ISTM that control-c must at least reset the stack, otherwise their 
is not easy way to get out. What can be left to another patch is doing a 
control-C for contents and then another one for the stack when there is no 
content.

Comments about v6:

> - error messages are now a bit more terse, following suggestions

Ok.

> - help text is more terse and Conditionals section was moved below Input
> Output

Ok.

> - leverage IFSTATE_NONE a bit to fold some not-in-a-branch cases into
> existing switch statements, giving flatter, slightly cleaner code and that
> addresses expected cases before exceptional ones

Code looks ok.

> - comments highlight which messages are printed in both interactive and
> script mode.

Yep.

> - put Fabien's tap test in place verbatim

Hmmm. That was really just a POC... I would suggest some more tests, eg:
  # elif error  "\\if false\n\\elif error\n\\endif\n"
  # ignore commands on error (stdout must be empty)  "\\if error\n\\echo NO\n\\else\n\\echo NO\n\\endif\n"

Also there is an empty line before the closing } of the while loop.

> - No mention of Ctrl-C or PROMPT. Those can be addressed in separate
> patches.

I think that Ctrl-C resetting the stack must be addressed in this patch. 
Trying to be more intelligent/incremental on Ctrl-C can wait for another 
time.

> There's probably some more consensus building to do over the interactive
> messages and comments,

Barking is now quite more verbose (?), but at least it is clear about the 
status and what is expected. I noticed that it is now always on, whether 
an error occured or not, which is ok with me.

> and if interactive-ish tests are possible with TAP, we should add those 
> too.

Good point. It seems that it is decided based on "source == stdin" plus 
checking whether both stdin/stdout are on terminal. Allowing to work 
around the later requires some more infrastructure to force "notty" (yuk, 
a negative variable tested negatively...) to false whatever, which does 
not seem to exist. So this is for another time.

-- 
Fabien.