The source project of this merge request has been removed.
Currently, the Window List applet will show an empty icon when focused on the desktop, meaning the button becomes invisible when it's set to only show icons (or on a vertical panel). It also doesn't show any icon if an application refers to an invalid icon (eg. An icon that can't be found on the disk).
Before:
| Window list on the desktop | Panel (Plasma Desktop) | Panel (App with invalid icon) | Icon-only mode with invalid icon or when focused on the Desktop |
|---|---|---|---|
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After:
| Window list on the desktop | Panel (Plasma Desktop) | Panel (App with invalid icon) | Icon-only mode with invalid icon or when focused on the Desktop |
|---|---|---|---|
 |
 |
 |
 
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Btw, there's no fallback icon on the window list itself that appears when you click the windowlist button on the panel. I think taskmanager provides the icons there for all task switchers, so changing that is outside the scope of this merge request.