Re: [PATCH v1 1/8] compat/terminal: let prompt accept input from pipe

From: Firmin Martin <firminmartin24@gmail.com>
To: Jeff King <peff@peff.net>, Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org,
	Johannes Schindelin <johannes.schindelin@gmail.com>,
	Erik Faye-Lund <kusmabite@gmail.com>,
	Denton Liu <liu.denton@gmail.com>
Subject: Re: [PATCH v1 1/8] compat/terminal: let prompt accept input from pipe
Date: Mon, 10 May 2021 06:18:36 +0200	[thread overview]
Message-ID: <875yzrgr1f.fsf@Inspiron.i-did-not-set--mail-host-address--so-tickle-me> (raw)
In-Reply-To: <YJTH+sTP/O5Nxtp9@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

Hi Peff,

> On Fri, May 07, 2021 at 08:37:49AM +0900, Junio C Hamano wrote:
>
>> Firmin Martin <firminmartin24@gmail.com> writes:
>> 
>> > Currently, git_prompt ignores input coming from anywhere other than
>> > terminal (pipe, redirection etc.) meaning that standard prompt
>> > auto-answering methods would have no effect:
>> >
>> >         echo 'Y' | git ...
>> >         yes 'Y' | git ...
>> >         git ... <input.txt
>> >
>> > It also prevents git subcommands using git_prompt to be tested using
>> > such methods.
>> 
>> For testing, wouldn't lib-terminal.sh be usable for your purpose?
>> If not, what is the reason why it is insufficient?  Can we fix that
>> instead?
>
> That doesn't work, because it insists on reading from /dev/tty and not
> the pty that lib-terminal will set up as stdin. But...
>
>> Allowing prompter to read from pipe has a big downside in the
>> production code: you cannot pipe data into our command, and let it
>> ask interactive questions from the end user by opening /dev/tty.
>
> Right. The main purpose of the function was to let git-remote-https,
> whose stdin is connected to git-fetch, get a password from the user.
> Reading from stdin would break things badly there[1].
>
> Looking at the second patch, the motivation here seems to be to use
> git_prompt() for another run-of-the-mill prompt. But the right answer
> is: don't do that. In fact, we recently-ish removed a similar case in
> 97387c8bdd (am: read interactive input from stdin, 2019-05-20) that was
> likewise causing problems with the test suite.

I actually inspired myself from the two occurrences of git_prompt in
builtin/bisect--helper.c introduced in 09535f056b (bisect--helper:
reimplement `bisect_autostart` shell function in C, 2020-09-24).
Not sure if they should also be converted to a simple fgets.
I will do that in the v2 of this series if the prompt is still proven useful.

>
> I think we might consider renaming git_prompt(), or adding an
> explanatory comment above it.

I would be happy to do that. A comment along the line of 97387c8bdd (am:
read interactive input from stdin, 2019-05-20) and a "CAUTION: don't use
it for regular prompt" would suffice ?

>
> -Peff
>
> [1] Sadly I don't think our test suite could notice the breakage
>     introduced by this function. It uses the askpass feature to avoid
>     triggering this code at all, because of course we can not reliably
>     read from /dev/tty in the script. But with just this patch applied,
>     and no credential helpers defined, trying "git ls-remote
>     https://github.com/you/some-private-repo" shows the problem: you get
>     prompted, but it never reads your input.

Many thanks for your comments,

Firmin