(Wayland) Add toplevel app id

[SaverinOnRails]

What does the pull request do?

Makes the Wayland backend set an app id instead of leaving this unset. An app id is required by freedesktop to load correct taskbar icons and such. Will default to ProcessName the way the x11 backend behaves if not set with WaylandPlatformOptions

What is the current behavior?

Wayland backend leaves app id unset.

What is the updated/expected behavior with this PR?

Wayland backend now sets app id. Will default to the process name if not explicitly set.

How was the solution implemented (if it's not obvious)?

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Fixed issues

Fixes #21783

New API

 .UseWaylandWithFallback()
    .With(new WaylandPlatformOptions{
         AppId = "myApp"
  })

[bolikcraft]

Drive-by review from someone who wrote the same patch a couple of hours later and is closing it in favour of this one (#21983) — a few notes that might be useful, take or leave them.

Default value. This defaults to Process.GetCurrentProcess().ProcessName, while X11PlatformOptions defaults WmClass to Assembly.GetEntryAssembly()?.GetName().Name in its constructor (ProcessName is used only for res_name in SetWmClass). Both are reasonable — the process name is often the better match for the desktop entry, since that is the name the binary is installed under — but the two Linux backends will report different identifiers for the same app unless one of them is aligned. Might be worth a maintainer's call on which one wins.

Empty string. appId ?? ProcessName only guards against null, so an explicitly empty AppId sends set_app_id(""). Treating empty as "not set" (either falling back or skipping the request) would make it possible to opt out.

Unrelated changes. The diff in WSurface.cs also reformats whitespace and brace style in CalculateMaxSize, EmitMinMaxSize, Resize and the Outputs declaration. It makes the app-id change harder to spot and will show up in git blame on those lines.

Naming. SetAppID reads oddly next to SetTitle and NWayland's own SetAppId.

Verified the behaviour this fixes on GNOME 49 (Wayland) with WAYLAND_DEBUG=1: before, no xdg_toplevel.set_app_id request is sent at all, so the window has no icon or name in the dash and the window switcher; StartupWMClass in the desktop entry does not help there, being X11-only.

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[SaverinOnRails]

Unrelated changes. The diff in WSurface.cs also reformats whitespace and brace style in CalculateMaxSize, EmitMinMaxSize, Resize and the Outputs declaration. It makes the app-id change harder to spot and will show up in git blame on those lines.

Yh sorry about the whitespace changes, my editor was formatting code on save with roslyn.

Default value. This defaults to Process.GetCurrentProcess().ProcessName, while X11PlatformOptions defaults WmClass to Assembly.GetEntryAssembly()?.GetName().Name in its constructor (ProcessName is used only for res_name in SetWmClass). Both are reasonable — the process name is often the better match for the desktop entry, since that is the name the binary is installed under — but the two Linux backends will report different identifiers for the same app unless one of them is aligned. Might be worth a maintainer's call on which one wins.

Agreed to leave this to maintainers' discretion.

[avaloniaui-bot]

You can test this PR using the following package version. 12.2.999-cibuild0068336-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[kekekeks]

PR has quite a lot of unrelated formatting/whitespace changes

[kekekeks]

Fallback should be here, I think.

[kekekeks]

simplify to direct call on _xdgTopLevel

[kekekeks]

I think we have a precedent of using Assembly.GetEntryAssembly()?.GetName().Name; as WM_CLASS with X11 (that matches desktop-files by StartupWMClass).

Have you checked if wayland is using the same matching mechanism for appid?

[kekekeks]

Qt has QGuiApplication::setDesktopFileName API that it uses for app_id.

[MrJul]

Notes from the API review meeting:
The API is accepted as is.

(The comments on the internally chosen default are still applicable.)