zunzuncito

For a couple of weeks now I have been using Plasma’s built-in weather report system. It supports various different sources for weather observations and forecasts, one of which is my preferred service, Deutscher Wetterdienst (DWD). Once the report location is set up, Plasma displays the current conditions in the tray - clicking on it gives you an overview of the next 7 days.

I’ve been quite pleased with this; a quick glance at the icon tells you everything you need to know and the forecast is only one click away. It even supports DWD’s official warning system. There is one small problem with the tray icon, however. See if you can spot it:

That’s right, I couldn’t have possibly taken this image given this post’s timestamp is before 23:57! Good catch. More importantly, however, the icon is showing the sun when realistically it’s going to be dark outside. This has been annoying me to no end, so a couple of days ago I decided to fix it.

Since Plasma already comes with weather icons suited for night-time use, I really only needed a reliable way to tell when to switch to those. After some spelunking in DWD’s two APIs, I found that the latter contains sunrise and sunset times for its forecast endpoint. The weather report system was already using this endpoint to fetch forecast data, so it was a rather simple lookup of two values in the API and then comparing the current observation time to those.

So, after some preparatory work to make date parsing more robust, I sent a merge request upstream which was promptly approved and merged. Finally I could rest easy after dusk, not having to worry about a sun chasing me around.

There’s some more stuff that could be improved in the DWD backend, like station availability. As far as I can tell, when using the open API, DWD limits access to weather data depending on whether or not they have the full rights to it. The API might therefore simply deny access to a station even though it is listed in in the official index. There’s no way to find out which station is accessible except to try them all. To get around this, the DWD backend uses a very simple heuristic based on the first digit of the station ID, since all stations starting with 0 or 1 seem to work. However, this ignores a number of other, still accessible, stations.

I’m planning to look into this further, hopefully finding a better solution so that users of the DWD backend have access to as many stations as possible.

Today, prompted by a question on the #kde channel on libera, I looked into how Plasma handles its registry of recently used folders and documents. Turns out it’s way more complicated than I first thought.

The question specifically was whether there was a way to programmatically add files to Okular’s recently opened documents, so that’s where I started looking. I was already aware that some apps like Okular and Gwenview keep their own history independently from the system, and I quickly found out that Okular simply keeps a list of recently opened files in its configuration file ~/.config/okularrc of all places.

This got me thinking. Maybe it would be a decent idea to instead have Okular interact with the system history directly. For that I first had to understand how exactly it worked.

The Standard

The way that I thought Plasma’s system history worked was through freedesktop.org’s Desktop Bookmark Specification . The gist of it is that applications read from and write to a well-known file $XDG_DATA_DIR/recently-used.xbel. Indeed that file existed and it even contained the relevant entry:

<bookmark href="IEEE%20Standard%20-%20POSIX%20Base%20Specifications,%20Issue%208,%202024.pdf">
<info>
  <metadata owner="http://freedesktop.org">
    <mime:mime-type type="application/pdf"/>
    <bookmark:applications>
      <bookmark:application name="org.kde.okular" exec="okular %u" count="1"/>
    </bookmark:applications>
  </metadata>
</info>
</bookmark>

Okular then seemed to write to both recently-used.xbel and okularrc when instead it could simply access the former directly and keep all history entries out of its configuration file. What’s more, having Okular forget its history would only clear the entry in okularrc.

The most prominent place in which system history is displayed is in Dolphin’s “Recent Files” panel. After clearing Okular’s history entry I still found the document there, so it seemed obvious to assume that it uses recently-used.xbel. Dolphin lets you forget specific entries from history, so I confidently deleted the entry there and re-checked the file. Weirdly, the entry was still there even though Dolphin didn’t show it anymore…

It was time to delve into the code. Untangling all the interconnected parts took a while, but after a good 10 minutes, I finally knew what was going on: There was another history provider.

The Other “Standard”

This is where I have to mention KDE’s activities. Activities are a somewhat ill-defined concept but they basically boil down to the idea of providing a different computing space depending on what you are doing at the moment. In reality the most obvious user-facing activity feature in Plasma 6 is that you can customize your task bar and wallpaper per activity so you could consider it an extension of virtual desktops - applications open on one activity won’t be shown once you switch to another.

Crucially, however, the activity subsystem kactivitymanagerd is also used to manage recently opened files. I imagine the plan is (or was) to enable tracking file history per activity, but in all my testing I could not get this to work - history seems to be global. So what this essentially means is that an application might, and most probably will:

1. Keep its own history, most of the time through KRecentFilesAction and a simplistic history implementation. The data here is exclusively accessed by the application itself.

2. Keep its history in the desktop-agnostic recently-used.xbel file. In KDE’s case this usually does not happen in the application itself but instead through its KIO framework. Other desktop systems might read and display this data, but KDE seems to be write-only: history is appended, but never shown to the user.

3. Keep its history in an SQLite database under ~/.local/share/kactivitymanagerd, managed by a daemon. This is what you see in Dolphin and what you can manage under “Recent Files” in the system settings.

It also means that if you want to tweak history management, forget documents or folders, or turn the thing(s) off, you have to look in a multitude of places:

1. If the application provides a setting to manage or disable its own history, use that. If that’s not available (like in Okular) you’re out of luck. Disabling an application’s own history will not impact the other two history providers - you will still see recent files in Dolphin and elsewhere in the system.

2. There’s been ongoing work to streamline management of entries in recently-used.xbel, spurred by this bug. You may also use the undocumented UseRecent, MaxEntries, and IgnoreHidden options read from ~/.config/kdeglobals.

3. Tweak kactivitymanagerd history in system settings under “Recent Files”.

Forgetting History

With all this in mind my immediate reaction is to shy away from the whole endeavour to have Okular interface with the system history - there’s too many moving parts, some of which aren’t even yet well-defined on KDE’s side.

For whatever reason I’ve been uncovering software bugs at an unprecedented rate in the past 10 days. This is by no means a bad thing, I enjoy hunting down and fixing bugs, but it does mean that the additional overhead of drafting a post about each bug becomes a bit too much. So instead here’s a quick overview - the linked patches and merge requests will have more information, if you are interested.

Trash size calculation in KIO

I noticed this one pretty much right after starting to use Dolphin but did not end up looking into it until quite a bit later: when displaying the size of the items in the trash, the application would always show 0 bytes. This would also cause the automated cleanup of items to fail - Dolphin simply believed that the trash was empty.

KDE uses the KIO framework to provide management of the trash. A recent commit had changed the construction of a QDirIterator in a way that would make it ignore all items when iterating over the trash directory. Thankfully the fix was straightforward and it was merged quickly.

git-shortlog(1) segfaults outside of a git repository

This one I uncovered as I was writing a small script to give me an overview of commit authors in all the git repositories I had cloned locally. I was happily scanning through my source directory using the --author flag for git-shortlog(1) to generate this, fully expecting git to complain about the few non-git directories I had. Instead of complaints, however, I got a segfault.

Turns out that a change back in May stopped setting SHA1 as the default object hash. This was done to progress the slow-moving transition to stronger hash functions but inadvertently broke git-shortlog(1) whose argument parsing machinery expected a default hash algorithm to be set. I sent a patch upstream.

An infinite loop in plasmashell

I regularly use the Activities functionality in Plasma 6 and switch through my activities using Plasma’s built-in activity manager. A couple of days ago I managed to make plasmashell, the provider for Plasma’s desktop and task bar, freeze - I had hit the “up arrow” key in the activity filter text box when there were no results visible. This was perfectly reproducible, so I went to investigate.

The cause of the issue was a do-while construct not handling a specific sentinel value, making it loop infinitely. For this one I also opened a merge request upstream.

For the last couple of months I have been running sway on my main desktop system after having been forced away from hikari because of its practically halted development and incompatibility with newer wlroots versions.

I never felt completely satisfied with it and the whole experience was rather joyless, so about a week ago I decided to give KDE Plasma 6 a try after a surprisingly decent experience on the KDE Neon live image.

Whilst undoubtedly greater in its complexity and code size than sway, to me Plasma 6 seems like one of the last decent desktop environments still remaining. It’s incredibly customisable (but still comes with good defaults), looks nice out of the box, and most importantly seems to care about providing a nicely integrated and featureful experience. This even includes a companion app on Android, KDE Connect. It remains to be seen whether it will fully convince me in the long run, but for now I am very satisfied with it.

This last week was mostly spent learning about the desktop environment and setting everything up exactly how I want it to be, but there were two notable bugs to squash as well.

The first one reared its ugly head once I enabled backwards-compatibility with Qt5-based apps. I have a couple of such apps still, most prominently Mumble and Quassel IRC. Once the latter was built against the KFramework libraries, no more notifications were shown…

Fixing this ended up taking about two days, most of which were spent discovering exactly how KNotifications work. KDE provides apps with a tighter integration to the notification service, allowing users to specify which types of notifications to show, and how. Applications specify their notifications by shipping an <app>.notifyrc file. KDE ties this file to the application by matching its base name to the name given to the application (usually through a call to QCoreApplication::applicationName or when creating KAboutData).

It turns out that Quassel had recently been patched to fix an issue where desktop environments did not show its icon correctly. This required a call to setDesktopFileName in KAboutData to make environments aware of the connection. However, Quassel’s application name was changed in the same commit, severing its link with the name given through its quassel.notifyrc file. This seems to have been done in addition to the setDesktopFileName call and was not necessary to solve the issue the commit was trying to address.

I prepared a pull request fixing this issue by reverting part of the offending commit.

The second bug I randomly came across whilst perusing journalctl and seeing the following error from Dolphin, KDE’s file manager:

QString(View)::contains(): called on an invalid QRegularExpression object
(pattern is '\A(?:file:///home/wolf/[Z-A]/?)\z')

Seeing this immediately made me wonder whether Dolphin plugs a URL straight into a regular expression without escaping it, and the answer, of course, is yes. I spent most of today’s afternoon hunting this issue down and preparing a merge request that fixes it in an elegant way.