[GTK] Make isWayland real check

[akurtakov]

And not just !isX11(). There are other backends like broadway, windows, quartz.

[github-actions]

Test Results

  115 files   -  3    115 suites   - 3   10m 43s ⏱️ - 1m 37s
4 546 tests  - 37  4 530 ✅  - 35  16 💤  - 2  0 ❌ ±0 
  311 runs   - 19    308 ✅  - 18   3 💤  - 1  0 ❌ ±0 

Results for commit 477704a. ± Comparison against base commit d87a932.

This pull request removes 37 tests.

AllGTKTests Test_GtkConverter ‑ test_HeuristicASCII_dollarSign
AllGTKTests Test_GtkConverter ‑ test_HeuristicASCII_emptyString
AllGTKTests Test_GtkConverter ‑ test_HeuristicASCII_letterA
AllGTKTests Test_GtkConverter ‑ test_HeuristicASCII_letters
AllGTKTests Test_GtkConverter ‑ test_HeuristicUTF16LE_null
AllGTKTests Test_GtkConverter ‑ test_HeuristicUTF16_AsciiLetters
AllGTKTests Test_GtkConverter ‑ test_HeuristicUTF16_Asciiletter
AllGTKTests Test_GtkConverter ‑ test_HeuristicUTF16_LotsOfLetters
AllGTKTests Test_GtkConverter ‑ test_HeuristicUTF16_letter
AllGTKTests Test_GtkConverter ‑ test_HeuristicUTF16_letters
…

[jonahgraham]

To the best of my understanding this looks ok.

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The rest of this is notes, perhaps more to record my own understanding than as a useful feedback on this PR.

There are a lot of assumptions that that !x11 is wayland (e.g. 1 2 3) - but since for now !x11 is effectively wayland for all active use cases I think having the explicit check is good here.

I can't get SWT to launch on Broadway with GTK3 or GTK4, but I haven't debugged why gtk_init_check fails (I can get the gtk4-demo/gtk3-demo to run in broadway)

To match what is documented in https://docs.gtk.org/gdk4/wayland.html I guess we could be harsher and error (or warn) if !isWayland && !isx11. But the reality is that there are not any active development in non-wayland/x11 area. Initiative 31 did some investigation on using GTK on Windows and macOS, but my guess is that would still require an awful lot of additional special casing before a really stable implementation would work. If that happened, change isX11/isWayland to an enum of known/supported backends may make sense.

With the potential complexity of GTK3 or GTK4 multiplied by the number of backends (x11, wayland and others such as those mentioned here) my understanding as documented in my recent blog post is still woefully under developed.

[akurtakov]

One reason to be explicit is to be a bit more future proof . Gtk 5 plans to drop X11 entirely (https://discourse.gnome.org/t/deprecated-x11-backend/30510 ) so having a "real" Wayland check is good idea. Merging.