Union in Plasma 6.7

[David Edmundson]

On Sat, May 16, 2026 at 1:21 PM Akseli <akselmo at akselmo.dev> wrote:
>
> On 15 May 2026 13.16.05 EEST, Nicolas Fella <nicolas.fella at gmx.de> wrote:
> >On 5/1/26 12:42 PM, Arjen Hiemstra wrote:
> >> Hi,
> >>
> >> With Plasma 6.7 we will have a release of Union, the new style engine that
> >> we've been working on for a while now. The current state is that we have a
> >> fully implemented QtQuick Controls style along with a Breeze reimplementation
> >> in CSS. Some of us have been daily driving it for a while now and while there
> >> are regressions, most of these are to the extent of slightly different paddings
> >> or mismatching colors.
> >>
> >> However, we cannot test all applications out there on our own, so we may have
> >> missed things. We really need more testing to figure out if there is major
> >> breakage and if so, how things break.
> >>
> >> This isn't really possible without a more general rollout of Union, so we had
> >> some discussion yesterday about what exactly we want to do for 6.7. I think
> >> there have been three options floated about:
> >>
> >> - We switch the default QtQuick Controls style. Since only Breeze is currently
> >> implemented in Union, switching it without some fallback would annoy people
> >> who don't use Breeze QtWidgets, so the current idea is to only use it when the
> >> user has selected Breeze. The main drawback is that there's no simple escape
> >> hatch for if an application does break to such and extent that it is unusable.
> >>
> >> - We add an option somewhere for users to opt in using Union. The advantage is
> >> that this could be fully opt-in. It could also explain more about what it is
> >> and what the state of things is in UI. The disadvantage is that for most users
> >> it is going to be a meaningless option that they won't fully know what the
> >> implications are, since it's mainly a technical option.
> >>
> >> - We do not do anything and rely on users setting `QT_QUICK_CONTROLS_STYLE` to
> >> Union. This I think is the worst outcome, as it makes it quite unlikely that
> >> many people use it, which means we don't get the testing coverage for Union
> >> that we need at this point.
> >>
> >> I know this discussion should have been started sooner, but the soft freeze
> >> date kinda snuck up on me, so here we are.
> >
> >Hi,
> >
> >sorry to be the party pooper here, but the whole rollout isn't going well:
> >
> >- The logic in https://invent.kde.org/plasma/plasma-integration/-/merge_requests/218 is flawed, Breeze needs to be Uppercase for it to trigger
> >
>
> I think this can be fixed, make it case insensitive.
>
> >- Most of our QML apps have QQuickStyle::setStyle("org.kde.desktop") in their main.cpp, overriding the default from plasma-integration
> >
>
> Why are apps doing this?

https://lxr.kde.org/search?%21v=kf6-qt6&_filestring=&_string=QQuickStyle%3A%3AsetStyle

At least 20.



>
> >- Distros are struggling to package Union due to Rust issues in cxx-rust-cssparser
> >
>
> For this I have seen couple MRs in Union already.
>
> >Given that this prevents useful testing during the beta we can't ship anything like this. Therefore https://invent.kde.org/plasma/plasma-integration/-/merge_requests/223
> >
> >Please try again for 6.8
> >
> >Cheers
> >
> >Nico
> >
>
> I'd like us to wait before jumping. I believe these issues can be fixed.