Bug 511547

Summary:	Wrong background color in top tool bar after switching to a different style
Product:	[Plasma] Breeze	Reporter:	Christian Aguilera <cristian64>
Component:	QStyle	Assignee:	Plasma Bugs List <plasma-bugs-null>
Status:	RESOLVED FIXED
Severity:	normal	CC:	akselmo, nate, nicolas.fella, noahadvs, uhhadd
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:	https://invent.kde.org/plasma/breeze/-/commit/3b00a0ee0e0b9cd6dc341e5811e3dc1451a18fc9	Version Fixed/Implemented In:	6.5.3
Sentry Crash Report:
Attachments:	Source code for a small Qt application (in C++) to demonstrate the issue. An animated GIF that shows that, after enabling the system style (Breeze), the background color in the top tool bar goes missing when other style (Fusion) is used.

Description Christian Aguilera 2025-11-02 21:08:29 UTC

Created attachment 186434 [details]
Source code for a small Qt application (in C++) to demonstrate the issue.

SUMMARY

The bizarre bug manifests after switching from Breeze to other Qt styles (e.g. Fusion).

This issue was previously reported to Qt in https://bugreports.qt.io/browse/QTBUG-141634 but, after some quick look at Breeze's source code, it appears that Breeze _may_ be the culprit.

STEPS TO REPRODUCE
1. Start a Qt application (which would be using the Breeze style in Plasma).
2. Switch to Fusion (assuming the application permits the switch, like in the `qt-tool-bars.cpp` attached example).
3. Attempt to set the `QPalette::window` / `QPalette::base` color in the Qt application (again assuming the application offers this action).

OBSERVED RESULT
The top tool bar (if it exists in the application) shows a background color that matches that color that Breeze would use.

EXPECTED RESULT
The top tool bar color should use the customized color set in the application palette.

Comment 1 Christian Aguilera 2025-11-02 22:32:19 UTC

Created attachment 186439 [details]
An animated GIF that shows that, after enabling the system style (Breeze), the background color in the top tool bar goes missing when other style (Fusion) is used.

Comment 2 Christian Aguilera 2025-11-02 22:46:07 UTC

It seems the problem is that `_listener` in `ToolsAreaManager` is never destroyed, therefore the tools area manager continues to operate even after a new `QStyle` has been set in the application.

This piece of code is what appears to be modifying the tool bars:

```cpp
    if (window->toolBarArea(toolbar) == Qt::TopToolBarArea) {
        widget->setPalette(palette());
        appendIfNotAlreadyExists(window, toolbar);
        return true;
    }
```
https://invent.kde.org/plasma/breeze/-/blob/e853447a8aaaa0ea0f04d0f43e05637272a4cbb6/kstyle/breezetoolsareamanager.cpp#L147-151

The potential fix would be:

```diff
diff --git a/kstyle/breezetoolsareamanager.cpp b/kstyle/breezetoolsareamanager.cpp
index f2aaec4..7254796 100644
--- a/kstyle/breezetoolsareamanager.cpp
+++ b/kstyle/breezetoolsareamanager.cpp
@@ -46,6 +46,7 @@ ToolsAreaManager::ToolsAreaManager()
 
 ToolsAreaManager::~ToolsAreaManager()
 {
+    delete _listener;
 }
 
 void ToolsAreaManager::loadSchemeConfig(const QString &path)
```

Comment 3 Akseli Lahtinen 2025-11-03 10:24:58 UTC

Would you be willing to make a merge request with the potential fix?

Comment 4 Christian Aguilera 2025-11-03 19:11:20 UTC

Merge request: https://invent.kde.org/plasma/breeze/-/merge_requests/560

Comment 5 Bug Janitor Service 2025-11-06 13:19:30 UTC

A possibly relevant merge request was started @ https://invent.kde.org/plasma/breeze/-/merge_requests/561

Comment 6 Nicolas Fella 2025-11-10 16:30:30 UTC

Git commit 506ab0e13bcf35dcf07a464b1830067131891639 by Nicolas Fella.
Committed on 10/11/2025 at 14:06.
Pushed by nicolasfella into branch 'master'.

[toolsareamanager] Reset palette on unpolish

We modify the palette of the widget, so when we change style we should be polite and restore the palette, otherwise the change will persist

M  +11   -0    kstyle/breezetoolsareamanager.cpp

https://invent.kde.org/plasma/breeze/-/commit/506ab0e13bcf35dcf07a464b1830067131891639

Comment 7 Nicolas Fella 2025-11-10 16:31:06 UTC

Git commit 3b00a0ee0e0b9cd6dc341e5811e3dc1451a18fc9 by Nicolas Fella.
Committed on 10/11/2025 at 16:31.
Pushed by nicolasfella into branch 'Plasma/6.5'.

[toolsareamanager] Reset palette on unpolish

We modify the palette of the widget, so when we change style we should be polite and restore the palette, otherwise the change will persist
(cherry picked from commit 506ab0e13bcf35dcf07a464b1830067131891639)

M  +11   -0    kstyle/breezetoolsareamanager.cpp

https://invent.kde.org/plasma/breeze/-/commit/3b00a0ee0e0b9cd6dc341e5811e3dc1451a18fc9