Re: What's cooking in git.git (Aug 2021, #02; Tue, 3)

From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: "SZEDER Gábor" <szeder.dev@gmail.com>,
	git@vger.kernel.org, "Taylor Blau" <me@ttaylorr.com>,
	"Emily Shaffer" <emilyshaffer@google.com>
Subject: Re: What's cooking in git.git (Aug 2021, #02; Tue, 3)
Date: Thu, 05 Aug 2021 04:53:12 +0200	[thread overview]
Message-ID: <871r78mw6w.fsf@evledraar.gmail.com> (raw)
In-Reply-To: <xmqq4kc4myme.fsf@gitster.g>

On Wed, Aug 04 2021, Junio C Hamano wrote:

> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
> [...]
>> By narrowly targeting a fix at one specific shell's cleverness around
>> COLUMNS we'll leave open a window where we'll fail on other shells if
>> they introduce similar cleverness.
>>
>> It hardly seems like a stretch that once bash starts doing that sort of
>> thing other shells might think to follow suit, and all have their own
>> non-standard way to turn it off.
>
> Hmph. Wouldn't the same argument apply to the much simpler single
> liner "shopt -u" solution?  When writing new tests, there is nothing
> to remember, and a new shell that needs a different trick to defeat
> the auto-COLUMNS would be detected quickly by running the tests in a
> terminal whose width is different from 80, no?

It's different in the "bisecting" case I mentioned. I.e. "shopt -u" is a
shell-specific solution, the approach I'm suggesting bypasses any sort
of shell-specific solutions, both current and future ones.

>> You also didn't address the other rationale for it, namely that it's
>> also future-proofing us for submarine breakages in non-git programs
>> which'll understand the new COLUMNS=10, but not GIT_TEST_COLUMNS=80.
>
> Isn't that another downside of the approach you are advocating?
>
> If we make Git rely on GIT_TEST_COLUMNS, we may honor it while
> everybody else ignores it.  If we only have to deal with COLUMNS
> like everybody else does, Git and other tools that are used in our
> tests will be affected the same way by overly-clever shells, no?

I think it's an upside. We know how git handles the combination of
GIT_TEST_COLUMNS, COLUMNS and TIOCGWINSZ. We have no idea how any
third-party program decides to behave.

So by intentionally spoiling COLUMNS=* and only having our tests pay
attention to GIT_TEST_COLUMNS we pretty much guarantee that we won't
grow some dependency on a non-git program's handling of COLUMNS, which
e.g. could differ from platform to platform.

I don't know about any such case, and spoiling COLUMNS didn't reveal
any. I just thought it was worthwhile to once-and-for-all get us away
from any sort of shell or 3rd party code cleverness around COLUMNS, as
opposed to a very narrow bugfix for just the issue we've spotted with
bash recently.