qt: add adwaita platform theme

[tschai-yim]

Description

This PR adds adwaita as an option to qt.platformTheme fixing #4702 and also NixOS/nixpkgs#295345 (the gnome option breaks some Qt6 tray applications). It also extends the configuraton interface to match qt.style which has a name and package sub-option for edge cases.

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all or nix develop --ignore-environment .#all using Flakes.

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Maintainer CC

@rycee @thiagokokada

[thiagokokada]

It also extends the configuraton interface to match qt.style which has a name and package sub-option for edge cases.

One reason I did not do this before is because those are all breaking changes, and there is no way to do this in a way that we could inform the users (e.g.: mkRenamedOption wouldn't work here).

So I am not sure about those changes. This will probably generate difficult to debug errors for the users.

[tschai-yim]

Added backwards compatibility with the following warning:

$ nix develop --ignore-environment .#qt-platform-theme-gnome
trace: warning: The option `qt.platformTheme` has been renamed to `qt.platformTheme.name`.
trace: warning: The value `gnome` for option `qt.platformTheme` is deprecated. Use `adwaita` instead.
bash: warning: setlocale: LC_NUMERIC: cannot change locale (de_CH.UTF-8): No such file or directory
bash: warning: setlocale: LC_TIME: cannot change locale (de_CH.UTF-8): No such file or directory
qt-platform-theme-gnome: OK

I think that should be enough for users to know what to do.

[thiagokokada]

LGTM, thanks for the backwards compatibility changes.

[tschai-yim]

@rycee @andresilva your comments should be resolved. You can rereview the code.

[rycee]

Thanks! Merged to master now 🙂

[oxalica]

It seems my QT theme breaks after the update, and it's mixing the light theme and dark theme together. I guess this PR may be relevant. Either using the original qt.platformTheme = "gnome" or the new qt.platformTheme.name = "adwaita"; has the same visual effect as screenshot below. Both dolphin from QT5 and QT6 suffer the visual issue. I'm not sure if my setting is the correct way to use Breeze-dark for QT apps.

The items are interleaving dark and light theme. (The grey box is just for redacted texts.)

My previously working configuration is here.

[Birdy2014]

The README of QAdwaitaDecorations says that it is a "Qt decoration plugin", not a platform theme and that it should be applied by setting the QT_WAYLAND_DECORATION environment variable.

I don't know much about Qt, but it seems to me like it doesn't make much sense to try to set QAdwaitaDecorations as a platform theme.