Make Konsole follow Plasma's light/dark color scheme

Steps#

1. Back up konsolerc, kdeglobals and your profiles.

   $ mkdir -p ~/konsole-backup
   $ cp -p ~/.config/konsolerc ~/.config/kdeglobals ~/.local/share/konsole/*.profile ~/konsole-backup/
   $ ls -1 ~/konsole-backup
   kdeglobals
   konsolerc
   user-default.profile
   

   Expected: the two config files and every .profile file. kdeglobals is in the list because step 5 writes to it.

2. Make a light twin of the dark profile. Put your names in the second line (mine are shown), then copy the dark profile under the new name with the light scheme:

   $ cd ~/.local/share/konsole
   $ DARK=user-default LIGHT=user-light LIGHT_SCHEME=islands-light
   $ sed -e "s/^Name=.*/Name=$LIGHT/" -e "s/^ColorScheme=.*/ColorScheme=$LIGHT_SCHEME/" "$DARK.profile" > "$LIGHT.profile"
   $ diff "$DARK.profile" "$LIGHT.profile"
   2c2
   < ColorScheme=islands-dark
   ---
   > ColorScheme=islands-light
   7c7
   < Name=user-default
   ---
   > Name=user-light
   

   Expected: exactly two lines differ, ColorScheme= and Name=. If diff shows only the Name= line, both profiles use the same scheme: Failure modes, row 2.

3. Turn on the sync and name the two profiles.

   $ kwriteconfig6 --file konsolerc --group LightDarkTheme --key SyncProfileWithSystemTheme true
   $ kwriteconfig6 --file konsolerc --group LightDarkTheme --key LightThemeProfile "$LIGHT"
   $ kwriteconfig6 --file konsolerc --group LightDarkTheme --key DarkThemeProfile "$DARK"
   $ kreadconfig6 --file konsolerc --group LightDarkTheme --key SyncProfileWithSystemTheme
   true
   $ kreadconfig6 --file konsolerc --group LightDarkTheme --key LightThemeProfile
   user-light
   $ kreadconfig6 --file konsolerc --group LightDarkTheme --key DarkThemeProfile
   user-default
   

   Expected: true, then the light and the dark name, spelled exactly as the profiles' Name= lines. Konsole looks the profiles up by that name; a name that matches no profile gets Konsole's built-in profile instead, without a message (source: ProfileManager.cpp; not tried).

   NoteEvery tab gets the pair

   Whenever a window opens and on each switch, Konsole sets the light or the dark profile on every session of that Konsole process, so a tab you opened with another profile changes to the pair too (source: applyThemeProfile() in MainWindow.cpp; not tried).

4. Open a test window in a new Konsole process.

   konsole --separate &
   

   Don't pass --profile: the sync has to choose the profile. --separate starts a new process, which reads konsolerc when it starts, even where Konsole is set to run all windows in one process (source: main.cpp; that option, UseSingleInstance, is off by default). To see the ANSI palette as well as the background, you can run this loop in the test window:

   for i in 0 1 2 3 4 5 6 7; do printf '\e[3%sm normal%s \e[9%sm bright%s \e[2;3%sm faint%s\e[0m\n' $i $i $i $i $i $i; done
   

   It comes from the script I used for one of that afternoon's light-mode screenshots (13:49). The live-switch window in Verify printed a single color0–color7 row instead, with a command I didn't record.

   Expected: the colors of the profile for Plasma's current mode. Plasma was dark here and the window came up dark, background pixel 24,25,27.

5. Switch Plasma to the other scheme and back while the test window is open. First, the scheme the session is on:

   $ kreadconfig6 --file kdeglobals --group General --key ColorScheme
   BreezeDark
   

   Expected: the current scheme's name. Here ~/.config/kdeglobals itself has no ColorScheme= line; the value comes from ~/.config/kdedefaults/kdeglobals, which is first in XDG_CONFIG_DIRS in my session. Switch to the other scheme first: by its source, plasma-apply-colorscheme given the scheme that is already set only reports that and changes nothing (not tried). Mine was BreezeDark, so:

   plasma-apply-colorscheme BreezeLight
   

   Wait about 4 s and look at the test window, then switch back:

   plasma-apply-colorscheme BreezeDark
   

   By its source (plasma-workspace 6.7.5), each successful call prints Successfully applied the color scheme <name> to your current Plasma session. Expected: the open window turns light, then dark again.

   Screenshots, for the screen half of Verify (optional): save the test window before the first command and about 4 s after each, as ~/konsole-test/1-dark-start.png, 2-after-light.png and 3-after-dark.png (names for a start in dark mode; mkdir -p ~/konsole-test first). I found the window with xdotool search --pid <PID> --onlyvisible, where <PID> is the konsole --separate process ($! right after step 4), and saved it with ImageMagick's import -window <WINDOW_ID> <FILE>. The exact command lines weren't recorded, and my files went to a different directory; I copied them into ~/konsole-test/ for the re-run in Field notes.

   Run both directions. On my box a window that comes up dark proves little: DefaultProfile is my dark profile, so with the sync off a new window is dark in dark mode too. The switch to light shows that the sync works. The switch back shows that the dark profile is still dark; if both profiles carry the light scheme (Failure modes, row 2), a window in light mode looks right either way.

   These two scheme names are the only ones I tried. My session was dark, on the Breeze Dark global theme (LookAndFeelPackage=org.kde.breezedark.desktop), so the round trip ended in dark mode, where it started. If you start in light mode or on another scheme, end on the one you started from [UNVERIFIED: not tried].

   Gotchaplasma-apply-colorscheme writes to kdeglobals

   After the round trip, ~/.config/kdeglobals had its own ColorScheme=BreezeDark line under [General] (step 6). A key in that file takes precedence over the kdedefaults value, so the scheme was now set in ~/.config/kdeglobals itself. I put the copy back so the file is as it was. Whether the extra line would block Plasma's automatic switching, I didn't check.

6. Put kdeglobals back.

   $ diff ~/konsole-backup/kdeglobals ~/.config/kdeglobals
   135a136
   > ColorScheme=BreezeDark
   $ cp -p ~/konsole-backup/kdeglobals ~/.config/kdeglobals
   $ diff ~/konsole-backup/kdeglobals ~/.config/kdeglobals
   

   Expected: the first diff shows what the test added (one line here). After the copy, diff prints nothing. The copy brings back the whole file as it was at step 1: if the first diff shows more than the ColorScheme= line, delete that one line in an editor instead (not tried). Don't remove it with kwriteconfig6 --delete: that leaves a ColorScheme[$d] marker behind (Failure modes, row 4). I didn't check what copying the file back does to a running session, so finish step 5 on the scheme you want to keep.

7. Close the test window and restart Konsole. By its source, Konsole applies the sync when a window is created and when its settings change from inside Konsole (MainWindow.cpp), and I didn't check whether a running Konsole notices an outside edit of konsolerc. A new Konsole process has it, as the test window did.