Avoid Closure cfunctions

[eschnett]

Gtk4.jl uses Closure cfunctions internally. These do not work on all architectures, e.g. they don't work on ARM, i.e. modern Apple laptops.

I see that there are two uses for closure cfunctions in the code:

gtype.jl:411:        deref = cfunction_(gc_unref_weak, Nothing, (Ref{typeof(x)},))
signals.jl:15:    callback = cfunction_(cb, RT, tuple(Ptr{GObject}, param_types..., Ref{CT}))

The first (in gtype.jl) always calls gc_unref_weak and thus doesn't need to be a closure at all, a regular cfunction would do.

The second (in signals.jl) does not need to be a closure either. The API has an additional argument data (see https://docs.gtk.org/gobject/func.signal_connect_data.html) that can be used to pass in additional information.

If changed, the exported function cfunction_, which always creates a closure cfunction, could be removed.

[jwahlstrand]

I think the issue goes much deeper; I count 189 total uses of @cfunction in this package.

[eschnett]

@cfunction itself is fine. The problem is when @cfunction is used with a $ sign on its first argument. That happens only in a few cases, and I think all these cases are wrapped in calls to cfunction_. I tried converting the code, but I'm not familiar with the GObject and gc_ref stuff, so I gave up.

(The Gtk4 tests fail on my laptop, that's how I noticed.)

By the way, Github actions now support running on ARM macOS hardware for testing, e.g. via

jobs:
  test:
    name: Julia ${{matrix.version}} - ${{matrix.os}} - ${{matrix.arch}} - ${{github.event_name}}
    runs-on: ${{matrix.os}}
    strategy:
      matrix:
        # See <https://julialang-s3.julialang.org/bin/versions.json> for available Julia versions
        include:
          - arch: "arm64"
            os: "macOS-14"
            version: "1.11"

This would allow testing Gtk4 on ARM hardware.

[jwahlstrand]

I see, thanks. I'll work on it soon.

[jwahlstrand]

Test should pass now on an ARM based Mac. Avoiding use of a closure cfunction in signals.jl is going to require a breaking change, it looks like to me, but should be possible with more work.