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

[Jeff King <peff@peff.net>]

On Tue, Sep 28, 2021 at 01:52:26AM +0200, Ævar Arnfjörð Bjarmason wrote:

> 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.

I'm not sure I agree. If you are willing to wrap git, then you can just
add:

  git -c include.path=~/.gitconfig.d/xyz.cfg

to the command-line in the first place. Or if you're willing to use our
undocumented interface, you can even do it in your .bashrc:

  if code_of_arbitrary_complexity
  then
          GIT_CONFIG_PARAMETERS="'include.path'='~/.gitconfig.d/xyz.cfg'"
  fi

The value of this env matching is that it is done at run-time without
wrapping, and can meaningfully inspect the state of the world. E.g., the
$TERM thing that started this thread.

> 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.

Yes, I have trouble imagining why any matching on env:PATH would be
useful (or $PWD, since we have the much less confusing gitdir
conditional). Which isn't to say I want to forbid it, but just because
people can shoot themselves in the foot with complexity doesn't mean
that "envIs" is a bad thing when it's not misused.

> > 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

Yeah, we talked about that a while ago, but nobody liked the interface
enough to actually code it (and as far as I know, it's really
theoretical; nobody has actually wanted to set such an option from the
command-line yet, and we have the --config-env stuff for people who want
to robustly pass along arbitrary keys).

A perhaps more subtle but less awkward to type version is to just
require two arguments, like:

  git --config <key> <value> ...

but I'd just as soon continue to leave it un-implemented if nobody has
actually needed it in practice.

-Peff