Re: [PATCH 2/2] config: allow specifying config entries via envvar pairs

From: Jeff King <peff@peff.net>
Date: Nov 17, 2020, 23:57 UTC
Message-ID: <20201117235736.GC642410@coredump.intra.peff.net>
In-Reply-To: <873618f4he.fsf@evledraar.gmail.com>

On Tue, Nov 17, 2020 at 03:22:05PM +0100, Ævar Arnfjörð Bjarmason wrote:

Show 19 quoted lines

> > 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).

Show 10 quoted lines

> 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

Looks like your mail got cut off. 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).

-Peff