KDE Review: Union and cxx-rust-cssparser

[Akseli Lahtinen]

On Thursday 26 February 2026 12:07:28 Eastern European Summer Time Arjen Hiemstra wrote:
> Hello all,
> 
> I'd like to start the review process for two projects, Union and its 
> dependency cxx-rust-cssparser. The relevant review issues are https://
> invent.kde.org/plasma/union/-/issues/115 for Union and https://invent.kde.org/
> libraries/cxx-rust-cssparser/-/issues/3 for cxx-rust-cssparser.
> 
> Union is a new style engine that intends to unify styling between the various 
> styling implementations we currently have, covering both QtQuick and 
> QtWidgets. It uses CSS as input format, though it is designed to allow 
> multiple input formats. The CSS input is powered by cxx-rust-cssparser which 
> is a thin C++ wrapper around a rust-based CSS parser built upon the rust 
> "cssparser" crate.
> 
> The current state is that we have a near-complete implementation of a QtQuick 
> style, along with a fairly complete implementation of Breeze in CSS. There is 
> also Kirigami integration on the QtQuick side. The QtWidgets side is still 
> rather limited, we can only style buttons at the moment. There will be more 
> progress there once we're finished with the QtQuick side.
> 
> The plan is to release Union along with Plasma 6.7, at the very least as a 
> "tech preview", but hopefully in such a state that we can start replacing our 
> other QtQuick styles. After a few releases I hope to make it a framework that 
> replaces all our styles, including the QtWidgets side.
> 
> To get to that state we'll need more testing however. If you want to help 
> test, running a QtQuick application with `QT_QUICK_STYLE=org.kde.union` after 
> building should run it with Union's QtQuick style. If you find any issues, do 
> let us know.
> 
> - Arjen
> 
> 
> 

Union review request items are now done.

https://invent.kde.org/plasma/union/-/issues/115 

Best regards,
- Akseli