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From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Jeff King <peff@peff.net>
Cc: Junio C Hamano <gitster@pobox.com>,
	Patrick Steinhardt <ps@pks.im>,
	git@vger.kernel.org
Subject: Re: [PATCH 2/2] config: allow specifying config entries via envvar pairs
Date: Wed, 18 Nov 2020 14:44:59 +0100	[thread overview]
Message-ID: <87ft56rd7o.fsf@evledraar.gmail.com> (raw)
In-Reply-To: <20201117235736.GC642410@coredump.intra.peff.net>


On Wed, Nov 18 2020, Jeff King wrote:

> On Tue, Nov 17, 2020 at 03:22:05PM +0100, Ævar Arnfjörð Bjarmason wrote:
>
>> > then I'd feel comfortable making it a public-facing feature. And for
>> > most cases it would be pretty pleasant to use (and for the unpleasant
>> > ones, I'm not sure that a little quoting is any worse than the paired
>> > environment variables found here).
>> 
>> I wonder if something like the git config -z format wouldn't be easier,
>> with the twist that we'd obviously not support \0. So we'd need an
>> optional length prefix. : = unspecified.
>> 
>>     :user.name
>>     Jeff K
>>     :alias.ci
>>     commit
>>     :10:bin.ary
>>     <10 byte string, might have a \n>
>>     :other.key
>>     Other Value
>> 
>> Maybe that's overly fragile, or maybe another format would be better.
>
> Yeah, length-delimited strings are an alternative that some people think
> is less error-prone than quoting. And we do use pkt-lines. They're also
> a pain for humans to write (it's nicer if they're optional, but when you
> _do_ have to start using them, now you are stuck counting things up).
>
>> I was trying to come up with one where the common case wouldn't
>> require knowing about shell quoting/unquoting, and where you could
>> still do:
>> 
>>     GIT_CONFIG_PARAMETERS=":my.new\nvalue\n$GIT_CONFIG_PARAMETERS"
>> 
>> Or equivalent, and still just keep $GIT_CONFIG_PARAMETERS as-is to pass
>> it along.
>> 
>> Your "do not require quoting" accomplishes that, and it's arguably a lot
>n
> Looks like your mail got cut off.

Nothing important, probably :)

> But yeah, the goal of making the quoting optional was to make it
> easier for humans to use for simple cases. It doesn't help at all with
> other programs inserting values, which can just as easily err on the
> side of caution.
>
> BTW, there is another problem with GIT_CONFIG_PARAMETERS (and "git -c"
> in general). The dotted config-key format:
>
>   section.subsection.key
>
> is unambiguous by itself, even though "subsection" can contain arbitrary
> bytes, including dots. Because neither "section" nor "key" can contain
> dots, we can parse from either end, and take the whole middle as a
> subsection (and this is how we do it in the code).
>
> But an assignment string like:
>
>   section.subsection.key=value
>
> _is_ ambiguous. We have to parse left-to-right up to the first equals
> (since "value" can contain arbitrary characters, including an equals).
> But "subsection" can have one, too, so we want to parse right-to-left
> there. E.g., in:
>
>   one.two=three.four=five
>
> this could be either of:
>
>   - section is "one", key is "two", value is "three.four=five"
>
>   - section is "one", subsection is "two=three", key is "four", value is
>     "five"
>
> We currently always parse it as the former (which I think is least-bad
> of the two, since values are more likely than subsections to contain
> arbitrary text with an equals).

Yeah, it's a pain to parse if it's on one line. FWIW that's the main
reason for why the format I suggested moved it to \n-delimited, because
keys can't contain an \n, so you can unambiguously have them be
\n-delimited (as git config -z does).

You do need to worry about a \n in the value, but for the common case
where you don't have a \n there we wouldn't need to provide the length.

Or just provide tooling as you suggested in
<20201118015907.GD650959@coredump.intra.peff.net>, which I like better
than any one format suggestion (including the one I suggsted). I.e. we
can document that:

 - The variable exists
 - You read/write/add to it using a return value from this tool

Which allows for keeping the value itself opaque and open to a future
change.

  reply	other threads:[~2020-11-18 13:46 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-13 12:16 [PATCH 0/2] " Patrick Steinhardt
2020-11-13 12:16 ` [PATCH 1/2] config: extract function to parse config pairs Patrick Steinhardt
2020-11-13 12:16 ` [PATCH 2/2] config: allow specifying config entries via envvar pairs Patrick Steinhardt
2020-11-13 13:04   ` Ævar Arnfjörð Bjarmason
2020-11-16 19:39     ` Junio C Hamano
2020-11-17  2:34       ` Jeff King
2020-11-17  6:37         ` Patrick Steinhardt
2020-11-17  7:01           ` Jeff King
2020-11-17 14:22         ` Ævar Arnfjörð Bjarmason
2020-11-17 23:57           ` Jeff King
2020-11-18 13:44             ` Ævar Arnfjörð Bjarmason [this message]
2020-11-18  0:50         ` brian m. carlson
2020-11-18  1:59           ` Jeff King
2020-11-18  2:25             ` brian m. carlson
2020-11-18  7:04               ` Patrick Steinhardt
2020-11-19  2:11                 ` brian m. carlson
2020-11-19  6:37                   ` Patrick Steinhardt
2020-11-18  5:44           ` Junio C Hamano
2020-11-17  6:28       ` Patrick Steinhardt
2020-11-17  7:06         ` Junio C Hamano
2020-11-18 13:49           ` Ævar Arnfjörð Bjarmason
2020-11-18 13:56             ` Patrick Steinhardt
2020-11-18 16:01             ` Junio C Hamano
2020-11-17 14:03       ` Ævar Arnfjörð Bjarmason
2020-11-13 16:37   ` Philip Oakley
2020-11-17  6:40     ` Patrick Steinhardt
2020-11-13 13:11 ` [PATCH 0/2] " Ævar Arnfjörð Bjarmason

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