From: Junio C Hamano <gitster@pobox.com>
Date: Tue, 27 Dec 2011 23:35:07 GMT
Subject: Re: [PATCH 1/5] add central method for prompting a user using GIT_ASKPASS or SSH_ASKPASS
Message-ID: <7vaa6d4mhg.fsf@alter.siamese.dyndns.org>
In-Reply-To: <CA+39Oz5J82GVyLfzWbWz20VS=Gp=8q9WsHQY33GuOKT1PyFCbQ@mail.gmail.com>

Thomas Adam <thomas@xteddy.org> writes:

> On 27 December 2011 20:47, Junio C Hamano <gitster@pobox.com> wrote:
>> Sven Strickroth <sven.strickroth@tu-clausthal.de> writes:
>>> +sub askpass_prompt {
>>> +     my ($self, $prompt) = _maybe_self(@_);
>>> +     if (exists $ENV{'GIT_ASKPASS'}) {
>>> +             return _askpass_prompt($ENV{'GIT_ASKPASS'}, $prompt);
>>> +     } elsif (exists $ENV{'SSH_ASKPASS'}) {
>>> +             return _askpass_prompt($ENV{'SSH_ASKPASS'}, $prompt);
>>> +     } else {
>>> +             return undef;
>>
>> Two problems with this if/elsif/else cascade.
>>
>>  - If _askpass_prompt() fails to open the pipe to ENV{'GIT_ASKPASS'}, it
>>   will return 'undef' to us. Don't we want to fall back to SSH_ASKPASS in
>>   such a case?
>>
>>  - The last "return undef" makes all callers of this method to implement a
>>   fall-back way somehow. I find it very likely that they will want to use
>
> Not only that, "return undef" will have nasty side-effects if this
> subroutine is called in list-context -- it's usually discouraged to
> have explicit returns of "undef", where in scalar context that might
> be OK, but in list context, the caller will see:
>
> (undef)
>
> and not:
>
> ()
>
> i.e., the empty list.

Well, for this particular function whose interface is "I'll give you a
prompt, use it to interact with the user and give me what the user gave us
in response", a scalar caller would do

	my $response = askpass_prompt("What is your password?");

while a list context caller would instead do

	my ($response) = askpass_prompt("What is your password?");

or

	my @answer = askpass_prompt("What is your password?");
        my $response = $answer[0];

and all three callers would get "undef" in $response. I suspect returning
(undef) is a better thing to do, than relying that

        my @answer = ();
        my $response = $answer[0];

happes to give undef to $response because the access goes beyond the end
of the array, no?