Subject: Re: [PATCH] config: add an includeIf.env{Exists,Bool,Is,Match}

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Tue, 28 Sep 2021 01:52:26 +0200

On Mon, Sep 27 2021, Jeff King wrote:

> On Mon, Sep 27, 2021 at 09:30:41AM -0700, Junio C Hamano wrote:
>
>> >> This asserts what? FOO=" bar"?
>> >
>> > Whoops, that should have been "envIs", asserting that $FOO contains
>> > "bar".
>> 
>> Oh, "can we check with a literal with leading whitespace?" was what
>> my question was about ;-)
>
> My assumption was that nobody would really care about doing so. It is
> true that it's less flexible, though (and is a decision we can't easily
> take back later).

Yeah, I think nobody really cares about stripspace() or not for this
sort of feature.

I do think having implicit and explicit complexity like that makes it
harder to document, implement and understand for users though. I.e. is
"env:FOO == bar" the same as "env:FOO ==bar" etc., what whitespace
exactly is accepted etc.

>> > As I said, I think it matters more with the infix operators, as:
>> >
>> >   [includeIf "env:FOO == bar"]
>> >
>> > is more readable than:
>> >
>> >   [includeIf "env:FOO==bar"]
>> 
>> Sure, but at that point, we'd probably want some quoting mechanism
>> for the literal to be compared, e.g.
>> 
>> 	[includeIf "env:PATH ~= \"(:|^)/usr/bin(:|$)\""]
>
> Ick. The extra quoting of the internal double-quotes is pretty horrid to
> look at. Also, how does one match a double-quote in the value? \\\"?
>
> If it were optional, that would make the common cases easy (no dq, no
> whitespace), and the hard ones possible.

An implicit assumption of mine in the simpler positive-match-only
version (which I should have made clear) is that anyone who needs this
sort of complexity can just arrange to wrap their "git" in a function,
or do this sort of thing in their ~/.bashrc, i.e. just:

    if code_of_arbitrary_complexity
    then
        export GIT_DO_XYZ_INCLUDES=1
    fi

Then in your config:

    includeIf.envBool:GIT_DO_XYZ_INCLUDES.path=~/.gitconfig.d/xyz.cfg

And having written that out I think the best thing to do is probably to
have a version that only does the envExists and envBool version (or just
envBool), and skip envIs and envMatch entirely.

In the case of env:PATH we're just setting users up for some buggy or
unexpected interaction with something that would be better done either
via a gitdir include, or if they really need $PATH they can just wrap
"git" in a function that sets a boolean inclusion variable.

That would get us out of having to support emergent behavior where some
git tool invoked via run_command() or something chdir's somewhere as an
implementation detail, and such an env:PATH match means we'd need to
support that, or potentially break existing user config.

Or, since we might not be invoked via a shell, the same issue with a
$PATH being "stale" from the POV of a user who's wondering why say a
command like:

    # status in the "t" subdirectory
    git -C t <cmd> <question>

Doesn't have the "right" $PWD, which we might not have as some future
shortcut in <cmd> decided not to bother chdir()-ing to answer the user's
<question>.

> I think this is getting into a bit of a digression, though. I'm willing
> to defer to Ævar, who is doing the actual work, and I don't know if he
> has found any of this compelling. ;)
>
>> > But I do think:
>> >
>> >   [includeIf "envIs:FOO:bar"]
>> >
>> > is harder to read than even:
>> >
>> >   [includeIf "envIs:FOO: bar"]
>> 
>> Hmph, that's quite subjective, I am afraid.  When I see the latter
>> in the configuration file, "do I have to have a single space before
>> 'bar' in the value of $FOO" would be the first question that would
>> come to my mind.
>
> I think it's just the mashed-up colons that I find ugly in the first
> one. But I agree the latter isn't that nice either, and introduces the
> ambiguity you describe.

FWIW I hacked up a --config-key --config-value pairing so you could set
keys with "=" in them on the command-line, I'm not sure I like the
interface, but it gets rid of that ":" v.s. "=" edge case:
https://github.com/avar/git/commit/a86053df48b

>> With an understanding that our syntax is so limited that we cannot
>> even write '=' and need to resort to Is: instead, I'd actually find
>> that the former less confusing than the latter.
>
> That I think is the most interesting question: is the "=" actually
> out-of-bounds? I tend to think not, based on our responses earlier in
> the thread.