Re: [PATCH 1/2] t3701: avoid one-shot export for shell functions

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 22, 2024, 23:57 UTC
Message-ID: <xmqqa5i96kvg.fsf@gitster.g>
In-Reply-To: <xmqqsew16lg9.fsf@gitster.g>

Junio C Hamano <gitster@pobox.com> writes:

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> Rubén Justo <rjusto@gmail.com> writes:
>
>> The common construct:
>>
>>     VAR=VAL command args
>>
>> it's a common way to define one-shot variables within the scope of
>> executing a "command".
>
> "it's a" -> "is a".
> "define" -> "set and export".
>
>> However, when "command" is a function which in turn executes the
>> "command", the behavior varies depending on the shell:
>>
>>  ** Bash 5.2.21 **
>>
>>     $ f () { bash -c 'echo A=$A'; }
>>     $ A=1 f
>>     A=1
>>
>>  ** dash 0.5.12-9 **
>>
>>     $ f () { bash -c 'echo A=$A'; }
>>     $ A=1 f
>>     A=1
>>
>>  ** dash 0.5.10.2-6 **
>>
>>     $ f () { bash -c 'echo A=$A'; }
>>     $ A=1 f
>>     A=

Another thing.  Let's insert a paragraph perhaps like this here.

    Note that POSIX explicitly says the effect of this construct
    used on a shell function is unspecified.

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>> One of our CI jobs on GitHub Actions uses Ubuntu 20.04 running dash
>> 0.5.10.2-6, so we failed the test t3701:51;  the "git add -p" being
>> tested did not get our custom GIT_PAGER, which broke the test.
>>
>> Work it around by explicitly exporting the variable in a subshell.

That way, we won't give a wrong impression that we can safely start using the construct in future once dash 0.5.10.2-6 goes away.