qt: install kio when qt.platformTheme = "kde"

[alyraffauf]

Description

Following discussions at NixOS/nixpkgs#362949, this PR fixes file dialogs when KDE is not installed but qt.platformTheme = "kde" (common for theming purposes). Without it, file dialogs fail to show files and folders. Only an issue when KDE is not installed, because KDE installs kio in its own module.

Checklist

• Change is backwards compatible.

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• 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

[doronbehar]

There is also a NixOS module option qt.platformTheme. Perhaps kde should be added there as well?

https://github.com/NixOS/nixpkgs/blob/65484f88b2c2175b3d06a8b5fd199bb852eee5e3/nixos/modules/config/qt.nix#L9

[rycee]

Thanks! Merged to master now 🙂