Patrick Steinhardt [off-list ref] writes:

The "git-gui" project has recently gained support for being built with
Meson, but it is not yet wired up in Git's own Meson build instructions.
"git-gui" itself is wired up as a standalone project, which means that
we can trivially make it available via `subproject("git-gui")`.

So far the theory. In practice thoguh the `subproject()` function comes

s/thoguh/though

with a couple of limitations. Most importantly, all subprojects need to
be contained in the same directory, and that directory cannot be the
top-level directory of the parent project. Right now we use the default
subproject directory ("subprojects/") for a couple of fallbacks in case
some important dependencies couldn't be found.

This means that we cannot just include the "git-gui" directory as a
subproject as it lives in our root directory. There are three options:

  - We move "git-gui" into "subprojects/". It requires a bit of churn,
    but should otherwise not have any significant downsides.

  - We create a symlink pointing from "subprojects/git-gui" to the
    top-level directory. This may not work on Windows.

  - We can create a "git-gui.wrap" file that knows to pull a specific
    commit from upstream and build it. This would mean that Meson and
    Makefiles now have different sources of truth for which version of
    "git-gui" we build.

The first option feels like the most sensible solution. It creates churn
and requires us to adapt the pull-request workflow a bit. But this
should be a one-time cost.

In theory we could also rename the "subprojects/" directory by passing
the "subproject_dir" argument to our `project()` call. But the name
feels quite fitting for our purpose, as well.

Okay makes sense. The most significant changes are in the top three
files and make sense.

[snip]