I have no idea why the checks are failing to compile. This compiles (and runs successfully) locally. All the "missing" symbols should be provided by <glib.h>.

It turns out the GLIB Version is too low.
The source specifies that it's only available from version >=2.74; but this is not shown in the docs.
The gir1.2-gtk-3.0 Ubuntu package depends on GLib >= 1.39.0 (currently 1.64.0-2), so this isn't available on Ubuntu, while on Arch, I'm running Glib2 2.80.3-2.

prolly the only way for you here is to IFDEF it

and mention that in the docs (also you didn't updated the doc aside of changing the type)

@actionless I added a (compile-time) version check. I tried to use ifdef, but for some reason it wouldn't detect as defined.

The new behavior has been added to the documentation

Is there anything left for me to do for this to be merged, or are we just waiting for another review?

see #3934

There is also the Build & Test / fixed-lgi-lua5.2 check that is unsuccessful. So the automatic merge wouldn't work anyway here.

@Aire-One If I understand correctly, that check is testing each commit to check that they all pass tests?
Should I squash the commits together to ensure that the (now one) commit passes?

yes

Alright, I've all the commits into the first (primary) commit.

From what I can tell, the CI checks failed during setup (and thusly not due to my code)

Apparently this is documented incorrectly, but the second argument of awful.spawn can be a table or "arguments". Please use that table for the new features. Adding more and more argument to the function doesn't scale. You end up with awful.spawn("cmd", false, nil, nil, nil, nil "something"), which is hard to read. (edit: Note that this is for the awful.spawn part of this, not the spawn.c/awesome.spawn part of it, which can have whatever API, I don't really care since this is a super low level obscure API only really used internally).

Also, the oldest still supported glib2 version appears to be 2.56 (for RHEL 8.8). Ubuntu 20.04 and 22.04 also have older versions. So 2.74 definitively will prevent people from building on a large number of totally supported distributions. This will require some ifdef, otherwise this can't be merged. You can do them in CMake by adding a new -D, but using normal #ifdef provided by glib2 is preferred. Because it breaks the most used LTS distributions, raising the glib2 version this far cannot be done for many more years. The most used Linux distro in the world right now, while the number are hard to get, is most probably Ubuntu 22.04.

I currently haven't touched awful.spawn, are you saying you'd like me to add this functionality there (as well)?

I currently do have the >2.74 functionality behind an #if GLIB_CHECK_VERSION(2,74,0), which is removed in versions <2.74. According to the GLib docs, all the other flags are available since 2.0.

This absolutely should build in its current state, without raising the minimum required GLib version. If i'm mistaken and that's not the case, please let me know so I can fix it.

The CI builds and tests pass on GLib version 2.64.6; so i'm fairly certain that this change is backwards-compatible.

--   Found glib-2.0, version 2.64.6