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From:   Junio C Hamano <gitster@pobox.com>
To:     Andreas Schwab <schwab@linux-m68k.org>
Cc:     Johannes Sixt <j6t@kdbg.org>,
        Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>,
        git@vger.kernel.org,
        Johannes Schindelin <johannes.schindelin@gmx.de>
Subject: Re: [PATCH v2 0/2] Brown-bag fix on top of js/mingw-inherit-only-std-handles
References: <pull.480.git.1575063876.gitgitgadget@gmail.com>
        <pull.480.v2.git.1575110200.gitgitgadget@gmail.com>
        <xmqq5zj12qc2.fsf@gitster-ct.c.googlers.com>
        <6beaf25f-1369-3e77-fd54-fdb5a1e63707@kdbg.org>
        <8736e5t98b.fsf@igel.home>
Date:   Sat, 30 Nov 2019 12:23:20 -0800
In-Reply-To: <8736e5t98b.fsf@igel.home> (Andreas Schwab's message of "Sat, 30
        Nov 2019 21:11:48 +0100")
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Andreas Schwab <schwab@linux-m68k.org> writes:

> On Nov 30 2019, Johannes Sixt wrote:
>
>> Am 30.11.19 um 19:04 schrieb Junio C Hamano:
>>> "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
>>> writes:
>>> 
>>>>  * We now assign errno only when the call to CreateProcessW() failed.
>>> 
>>> Meaning the global variable 'errno' is left as it was (instead of
>>> getting cleared) when a system call succeeds?  That I think is the
>>> correct behaviour people who use the variable expect.
>>
>> I hope you mean people who read the code. You cannot possibly mean
>> developers who expect that the run-command API keeps errno unchanged if
>> the calls were successful. I'm pretty sure they do not provide such a
>> guarantee.
>
> POSIX guarantees that no library function sets errno to zero.

It is true, but the rest of the Git code works on top of an
abstraction a bit higher than C/POSIX library.  The run-command API
J6t cites is an example.

IOW, we cannot take advantage of that POSIX guarantee in the
codepaths that use our internal API.  So...