Re: git makes it impossible to ignore or override global gitconfig, needs `GITCONFIGFILE`

[Timothee Cour <timothee.cour2@gmail.com>]

* GIT_CONFIG doesn't work as you mentioned and as was already
mentioned in https://stackoverflow.com/questions/23400449/how-to-make-git-temporarily-ignore-gitconfig
* `HOME= `doesn't work for many reasons: it breaks other commands as
you mentioned, it breaks `~`, and it doesn't work if users' git config
is in /Users/timothee/.config//git/config ; and pointing it to an
alternate home where you'd have `newhome/.gitconfig`  would require a
lot of workarounds to update paths including `~`
*  `XDG_CONFIG_HOME= ` also doesn't work (even if users' git config is
in /Users/timothee/.config//git/config), which really seems buggy,
eg:`XDG_CONFIG_HOME= git diff HEAD^` is still reading
`/Users/timothee/.config//git/config` somehow
* GIT_CONFIG_NOGLOBAL is also not good, I want to be able to simply
point my config to some place else, not simply suppress reading git
config
* require passing commands (eg `git -c`) is not good either; it'd
require updating scripts that rely on git (this could be arbitrarily
complex, sometimes impossible if you just have a binary and no source
code access)

In contrast, what I'm suggesting is extremely simple to use, robust,
and my understanding is it shouldn't be hard to implement.
```
GITCONFIGFILE=   git diff HEAD^ # empty config
GITCONFIGFILE=/pathto/gitconfig2   git diff HEAD^ # uses specified git
config file
GITCONFIGFILE=/pathto/gitconfig2   run_some_complex_script # uses
specified git config file everywhere
```
by contrast, any approach based on passing command line flag (eg `git
-c /pathto/gitconfig2 diff HEAD^`) will make the last case impossible
to do since you'd need to update every git command inside (which could
be in a compiled binary, etc)

What i'm asking is the analog of `TIGRC_USER` for tig
(https://jonas.github.io/tig/doc/tig.1.html) and many other programs

On Thu, Mar 19, 2020 at 9:51 AM Jeff King <peff@peff.net> wrote:
>
> On Thu, Mar 19, 2020 at 06:44:07AM +0000, Eric Wong wrote:
>
> > Timothee Cour <thelastmammoth@gmail.com> wrote:
> > > git makes it impossible to ignore global gitconfig. This is
> > > essentially what's being asked here:
> > > https://stackoverflow.com/questions/23400449/how-to-make-git-temporarily-ignore-gitconfig
> > >
> > > ## proposal:
> > > add an environment variable (like for tig and other programs), eg:
> > > `GITCONFIGFILE=~/.gitconfig_temp git diff`
> > > seems like an easy change that would make it easy for users to ignore
> > > or override their gitconfig
> >
> > You can use GIT_CONFIG for that, and there's also
> > GIT_CONFIG_NOSYSTEM.  They're both documented in the
> > git-config(5) manpage.
>
> I don't think $GIT_CONFIG is what Timothee whats. It only affects the
> git-config command, not config lookup in other programs. And it
> overrides _all_ config lookup, as if "git config --file" had been used.
>
> There's no variable to suppress just the user-level gitconfig. The usual
> technique (that we use in the test scripts) is to point $HOME somewhere
> else, but that may affect other programs.
>
> I wouldn't be opposed to GIT_CONFIG_NOGLOBAL if there's a use case, but
> it sounds like the desire is to actually provide new config. That can
> also be done for specific options with "git -c". Under the hood that is
> using GIT_CONFIG_PARAMETERS in the environment; you can set it
> individually, but note that it's a little picky about quoting (the
> individual keys are shell-quoted, but it insists that there is an outer
> layer of single-quotes, even if they weren't necessary; I wouldn't be
> opposed to making it more friendly). You can see what it produces like
> this:
>
>   git -c alias.dump='!echo "$GIT_CONFIG_PARAMETERS"' dump
>
> -Peff