Re: [PATCH v5 3/3] config: allow overriding of global and system configuration

> On Mon, Apr 19, 2021 at 02:31:16PM +0200, Patrick Steinhardt wrote:
> > In order to have git run in a fully controlled environment without any
> > misconfiguration, it may be desirable for users or scripts to override
> > global- and system-level configuration files. We already have a way of
> > doing this, which is to unset both HOME and XDG_CONFIG_HOME environment
> > variables and to set `GIT_CONFIG_NOGLOBAL=true`. This is quite kludgy,
> > and unsetting the first two variables likely has an impact on other
> > executables spawned by such a script.
> > 
> > The obvious way to fix this would be to introduce `GIT_CONFIG_NOGLOBAL`
> > as an equivalent to `GIT_CONFIG_NOSYSTEM`. But in the past, it has
> > turned out that this design is inflexible: we cannot test system-level
> > parsing of the git configuration in our test harness because there is no
> > way to change its location, so all tests run with `GIT_CONFIG_NOSYSTEM`
> > set.
> > 
> > Instead of doing the same mistake with `GIT_CONFIG_NOGLOBAL`, introduce
> > two new variables `GIT_CONFIG_GLOBAL` and `GIT_CONFIG_SYSTEM`:
> > 
> >     - If unset, git continues to use the usual locations.
> > 
> >     - If set to a specific path, we skip reading the normal
> >       configuration files and instead take the path. By setting the path
> >       to `/dev/null`, no configuration will be loaded for the respective
> >       level.
> > 
> > This implements the usecase where we want to execute code in a sanitized
> > environment without any potential misconfigurations via `/dev/null`, but
> > is more flexible and allows for more usecases than simply adding
> > `GIT_CONFIG_NOGLOBAL`.
> 
> Something is still not right with this patch series, because:
> 
> > +test_expect_success 'write to overridden global and system config' '
> > +	cat >expect <<EOF &&
> > +[config]
> > +	key = value
> > +EOF
> > +
> > +	GIT_CONFIG_GLOBAL=write-to-global git config --global config.key value &&
> > +	test_cmp expect write-to-global &&
> > +
> > +	GIT_CONFIG_SYSTEM=write-to-system git config --system config.key value &&
> > +	test_cmp expect write-to-system
> > +'
> 
> This test fails on Travis CI's Linux32 job:
> 
>   expecting success of 1300.184 'write to overridden global and system config': 
>   	cat >expect <<EOF &&
>   [config]
>   	key = value
>   EOF
>   	GIT_CONFIG_GLOBAL=write-to-global git config --global config.key value &&
>   	test_cmp expect write-to-global &&
>   	GIT_CONFIG_SYSTEM=write-to-system git config --system config.key value &&
>   	test_cmp expect write-to-system
>   + cat
>   + GIT_CONFIG_GLOBAL=write-to-global git config --global config.key value
>   fatal: unable to access '/root/etc/gitconfig': Permission denied
>   error: last command exited with $?=128
>   not ok 184 - write to overridden global and system config

> Yeah, that job has a weird environment with Docker and 'su'
> interacting in a way that ultimately builds Git with 'HOME=/root',
> which in our build system means that 'sysconfdir=/root/etc'.  To
> reproduce at home just run:
> 
>   make prefix=/root && cd t && ./t1300-config.sh -V -x -i

> test_expect_success 'override global and system config' '
>         test_when_finished rm -f "$HOME"/.config/git &&
> 
>         cat >"$HOME"/.gitconfig <<-EOF &&
>         [home]
>                 config = true
>         EOF
>         mkdir -p "$HOME"/.config/git &&
>         cat >"$HOME"/.config/git/config <<-EOF &&
>         [xdg]
>                 config = true
>         EOF
>         cat >.git/config <<-EOF &&
>         [local]
>                 config = true
>         EOF
>         cat >custom-global-config <<-EOF &&
>         [global]
>                 config = true
>         EOF
>         cat >custom-system-config <<-EOF &&
>         [system]
>                 config = true
>         EOF
> 
>         cat >expect <<-EOF &&
>         global  xdg.config=true
>         global  home.config=true
>         local   local.config=true
>         EOF
>         git config --show-scope --list >output &&
>         test_cmp expect output &&
> 
>         sane_unset GIT_CONFIG_NOSYSTEM &&

>         cat >expect <<-EOF &&
>         system  system.config=true
>         global  global.config=true
>         local   local.config=true
>         EOF
>         GIT_CONFIG_SYSTEM=custom-system-config GIT_CONFIG_GLOBAL=custom-global-config \
>                 git config --show-scope --list >output &&
>         test_cmp expect output &&
> 
>         cat >expect <<-EOF &&
>         local   local.config=true
>         EOF
>         GIT_CONFIG_SYSTEM=/dev/null GIT_CONFIG_GLOBAL=/dev/null git config --show-scope --list >output &&
>         test_cmp expect output
> '