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From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>,
	git@vger.kernel.org,
	"Johannes Schindelin" <johannes.schindelin@gmx.de>,
	마누엘 <nalla@hamal.uberspace.de>
Subject: Re: [PATCH] clean: explicitly `fflush` stdout
Date: Wed, 8 Apr 2020 18:38:21 -0400	[thread overview]
Message-ID: <20200408223821.GD3468797@coredump.intra.peff.net> (raw)
In-Reply-To: <xmqqr1wxoddc.fsf@gitster.c.googlers.com>

On Wed, Apr 08, 2020 at 02:51:11PM -0700, Junio C Hamano wrote:

> > Agreed. I guess it didn't affect people on other platforms much because
> > stdout to a terminal is generally line-buffered on POSIX systems. But
> > it's better not to rely on that, plus it could create confusion if
> > somebody tried to manipulate the interactive operation through a pipe
> > (e.g., driving it from a GUI or something).
> 
> Hmph, I thought it was more common to do prompts etc. on the
> standard error stream, which tends to make the buffering of the
> output less of a problem, but apparently these prompts are given to
> the standard output.

The prompts in git-add--interactive.perl go to stdout, as do the ones
for "am --interactive". I think that's reasonable, if you think of it as
the main output of the program.

At one point the "am" ones actually went to /dev/tty, but IMHO that's a
mistake. In 99% of cases it behaves the same as looking at stdin/stdout
(because they're connected to the terminal anyway), and in the other 1%
it's just as likely to be the wrong thing as the right. Plus it makes
testing much harder.

> I am also OK to sprinkle fflush(stdout) but in
> the longer term, it would probably be a good idea to introduce a
> helper to "prompt then grab input" or "read user input" (if the
> former, we'd be able to bring consistency into "which between the
> standard output or the standard error does a prompt come?", and if
> the latter we'd do fflush(NULL) before reading), especially if there
> are many git subcommands that go interactive.

Agreed. There is git_prompt(), but that does the tty thing, which I
think we'd want to avoid in most cases. It's used by the credential
code, which really does want to use a terminal to do things like turn
off character echoing. Plus it's not the main function of the program,
but rather a side effect (so we have to avoid disrupting the main
stdin/stdout).

-Peff

  reply	other threads:[~2020-04-08 22:38 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-08 19:33 Johannes Schindelin via GitGitGadget
2020-04-08 20:14 ` Jeff King
2020-04-08 21:51   ` Junio C Hamano
2020-04-08 22:38     ` Jeff King [this message]
2020-04-10 14:03   ` Johannes Schindelin
2020-04-10 11:27 ` [PATCH v2 0/2] Explicitly fflush stdout in git clean Johannes Schindelin via GitGitGadget
2020-04-10 11:27   ` [PATCH v2 1/2] Refactor code asking the user for input interactively Johannes Schindelin via GitGitGadget
2020-04-10 12:27     ` Derrick Stolee
2020-04-10 14:01       ` Johannes Schindelin
2020-04-10 15:07     ` Jeff King
2020-04-10 17:44     ` Junio C Hamano
2020-04-10 11:27   ` [PATCH v2 2/2] Explicitly `fflush` stdout before expecting interactive input 마누엘 via GitGitGadget
2020-04-10 12:28     ` Derrick Stolee
2020-04-10 18:16   ` [PATCH v3 0/2] Explicitly fflush stdout in git clean Johannes Schindelin via GitGitGadget
2020-04-10 18:16     ` [PATCH v3 1/2] Refactor code asking the user for input interactively Johannes Schindelin via GitGitGadget
2020-04-10 18:16     ` [PATCH v3 2/2] Explicitly `fflush` stdout before expecting interactive input 마누엘 via GitGitGadget

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