content: Add post: "Understanding recent files on KDE Plasma 6"

1 files changed, 131 insertions, 0 deletions

diff --git a/content/25/index.md b/content/25/index.md
new file mode 100644
index 0000000..b17f3fe
--- /dev/null
+++ b/content/25/index.md
@@ -0,0 +1,131 @@
++++
+date = 2024-10-18T17:46:30+02:00
+title = "Understanding recent files on KDE Plasma 6"
+
+[taxonomies]
+tags = ["TIL", "kde"]
+
+[extra]
+related = []
++++
+
+Today, prompted by a question on the `#kde` channel on
+[libera](https://libera.chat/), 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](https://okular.kde.org/) recently opened documents, so
+that's where I started looking. I was already aware that some apps like Okular
+and [Gwenview](https://apps.kde.org/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.
+
+{{ img(path="recent-okular.png", format="png", alt="A screenshot of Okular,
+KDE's PDF document viewer. The application shows its welcome page, with a button
+to open a new document beside a list of recently opened documents. The latter
+contains an entry for a PDF of the POSIX Base Specifications.",
+caption="Okular's welcome page, with recent documents listed.") }}
+
+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](https://www.freedesktop.org/wiki/Specifications/desktop-bookmark-spec/)
+. 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:
+
+```xml
+<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](https://apps.kde.org/dolphin/) "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](https://pointieststick.com/2024/02/06/whats-going-on-with-activities-in-plasma-6/)
+[ill-defined](https://invent.kde.org/plasma/kactivitymanagerd/-/issues/6)
+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`](https://invent.kde.org/plasma/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](https://api.kde.org/frameworks/kconfigwidgets/html/classKRecentFilesAction.html)
+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](https://invent.kde.org/frameworks/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](https://www.sqlite.org/) 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](https://invent.kde.org/frameworks/kio/-/merge_requests/1670)
+[work](https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/4560) to
+streamline management of entries in `recently-used.xbel`, spurred by [this
+bug](https://bugs.kde.org/show_bug.cgi?id=480276). You may also use the
+undocumented `UseRecent`, `MaxEntries`, and `IgnoreHidden`
+[options](https://invent.kde.org/frameworks/kio/-/blob/57342c46bf3789cd6f7b07ec33086a24f26223ad/src/core/krecentdocument.cpp#L512-515)
+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.