"Where does Unity store its launch bar items?" or "Convincing Ubuntu's Unity 7.4.5 to run the newer version of PyCharm when starting from the launcer"

I have been driving a System76 Oryx-Pro for some time now. And I am running Ubuntu 16.04 on it.
I typically try to avoid polluting global name spaces, so any apps I install from source I tend to install under a versioned directory under ~/opt, for instance, PyCharm Community Edition 2016.3.1 is installed under ~/opt/pycharm-community-2016.3.1.

Today, after Pycharm suggested I install a newer version, I downloaded the current package, and ran it, as instructed in the embedded readme.txt, via the wrapper script:

~/opt/pycharm-community-2018.1.2/bin$ ./pycharm.sh

Everything looked OK, but when wanting to lock the icon on the launch bar I realized Unity did not display a separate Pycharm Community Edition icon for the 2018.1.2 version, but showed the existing icon as active.

"I guess it's the same filename, so maybe unity confuses the older version with the new one, so I have to replace the launcher to user the newer version by default", I said.

So I closed the interface, then removed the PyCharm Community Edition, then I restarted the newer Pycharm from the command line, then blocked the icon, then I closed PyCharm once more, then clicked on the launcher bar.

Surprise! Unity was launching the old version! What?!

Repeated the entire series of steps, suspecting some PEBKAC, but was surprised to see the same result.

"Damn! Unity is stupid! I guess is a good thing they decided to kill it!", I said to myself.

Well, it shouldn't be that hard to find the offending item, so I started to grep in ~/.config, then in ~/.* for the string "PyCharm Cummunity Edition" without success.
Hmm, I guess the Linux world copied a lot of bad ideas from the windows world, probably the configs are not in ~/.* in plain text, they're probably in that simulacrum of a Windows registry called dconf, so I installed dconf-editor and searched once more for the keyword "Community", but only found one entry in the gedit filebrowser context.

So where does Unity gets its items from the launchbar? Since there is no "Properties" entry context menu and didn't want to try to debug the starting of my graphic environment, but Unity is open source, I had to look at the sources.

After some fighting with dead links to unity.ubuntu.com subpages, then searching for "git repository Ubuntu Unity", I realized Ubuntu loves Bazaar, so searched for "bzr Ubuntu Unity repository", no luck. Luckly, Wikipedia usually has those kind of links, and found the damn thing.

BTW, am I the only one considering some strong hits with a clue bat the developers which name projects by some generic term that has no chance to override the typical term in common parlance such as "Unity" or "Repo"?

Finding the sources and looking a little at the repository did not make it clear which was the entry point. I was expecting at least the README or the INSTALL file would give some relevant hints on the config or the initalization. M patience was running dry.

Maybe looking on my own system would be a better approach?

eddy@feodora:~$ which unity
/usr/bin/unity
eddy@feodora:~$ ll $(which unity)
-rwxr-xr-x 1 root root 9907 feb 21 21:38 /usr/bin/unity*
eddy@feodora:~$ ^ll^file
file $(which unity)
/usr/bin/unity: Python script, ASCII text executable

BINGO! This looks like a python script executable, it's not a binary, in spite of the many .cpp sources in the Unity tree.

I opened the file with less, then found this interesting bit:

 def reset_launcher_icons ():
    '''Reset the default launcher icon and restart it.'''
    subprocess.Popen(["gsettings", "reset" ,"com.canonical.Unity.Launcher" , "favorites"])

Great! So it stores that stuff in the pseudo-registry, but have to look under com.canonical.Unity.Launcher.favorites. Firing dconf-editor again found the relevant bit in the value of that key:

'application://jetbrains-pycharm-ce.desktop'

So where is this .desktop file? I guess using find is going to bring it up:

find /home/eddy/.local/ -name jetbrains* -exec vi {} \;

It did, and the content made it obvious what was happening:

[Desktop Entry]
Version=1.0
Type=Application
Name=PyCharm Community Edition
Icon=/home/eddy/opt/pycharm-community-2016.3.1/bin/pycharm.png
Exec="/home/eddy/opt/pycharm-community-2016.3.1/bin/pycharm.sh" %f
Comment=The Drive to Develop
Categories=Development;IDE;
Terminal=false
StartupWMClass=jetbrains-pycharm-ce

Probably Unity did not create a new desktop file when locking the icon, it would simply check if the jetbrains-pycharm-ce.desktop file existed already in my.local directory, saw it was, so it skipped its recreation.

Just as somebody said, all difficult computer science problems are eiether caused by leaky abstractions or caching. I guess here we're having some sort of caching issue, but is easy to fix, just edit the file:

eddy@feodora:~$ cat /home/eddy/.local/share/applications/jetbrains-pycharm-ce.desktop

[Desktop Entry]
Version=1.0
Type=Application
Name=PyCharm Community Edition
Icon=/home/eddy/opt/pycharm-community-2018.1.2/bin/pycharm.png
Exec="/home/eddy/opt/pycharm-community-2018.1.2/bin/pycharm.sh" %f
Comment=The Drive to Develop
Categories=Development;IDE;
Terminal=false
StartupWMClass=jetbrains-pycharm-ce

Checked again the start, and now the expected slash screen appears. GREAT!

I wonder if this is a Unity issue or is it due to some broken library that could affect other desktop environments such as MATE, GNOME or XFCE?

"Only" lost 2 hours (including this post) with this stupid bug, so I can go back to what I was trying in the first place, but now is already to late, so I have to go to sleep.