Can't you make a property where the applet tells it the size it likes to have, similar to what you do with the drag pixmap size?

No clue, this "fixme" was already there, I'm only optimizing for speed. I'll let Eike reply to this.

Oops, didn't see it. I'll adjust the patch.

However this makes me wonder, given this code

if (!data.icon.name().isEmpty()) {
    return data.url;
}

do I still need to handle the case where data.icon is set (non-null, but no name either, i.e. not from a theme, can this happen?)

Not in XWindowsTasksModel. The way it works is that Private::windowUrl() builds an URL for the window from window/process metadata using a heuristic, then TaskTools::appDataFromUrl() gets app data from it. appDataFromUrl() can set a QIcon without a name in two cases: When it's passed a fallback QIcon to use which lacks a name, and when it reads a pixmap from the URL's query string. The URLs produced by windowUrl() have no query string with an icon yet (obviously), and don't call appDataFromUrl() with a fallback icon (since the fallback is the window icon pixmap). tl;dr: No you don't need to handle that case.