I was in this situation recently: An application icon would not show up in GNOME shell, even after I double- and triple-checked that I did all the right things:
- Installed the desktop file with the right name in /usr/share/applications
- Installed the icon with the right name in the hicolor icon theme
- Make sure that Icon key in the desktop file has the right name
- Restart GNOME shell (this is necessary due to a bug where GNOME shell will not reliably pick up desktop file changes)
Still, I just get the generic executable icon: 
GNOME shell to the rescue
I asked GNOME shell maintainer Florian Müllner for help. He said: GNOME shell is probably picking up a stale desktop file from somewhere.
But from where ? I checked all the locations listed in XDG_DATA_DIRS to no avail. At this point, I was getting desperate, so I went back to Florian. He said: Just use looking glass to find out! If you don’t remember, looking glass is a pretty handy debugging console that is built right into GNOME shell. You open it by typing the command
lg
Into the Alt-F2 run dialog.
This brings up the looking glass. Here is how it helped me solve my problem:
I switched to the window tab, then clicked on the application in question, and hit the ‘Insert’ button. That binds the object to a variable named r(x) (for some number x) in the Javascript evaluator.
Going there, I then typed the command
r(3).app_info.get_filename()
And that showed the problematic desktop file:
I removed that file and restarted the shell once more, and now everything is working as it should:
Thanks, looking glass!
All I get is (I tried with all my open windows).
Do you know what may be causing this error?
“exception TypeError: r(…).app_info is undefined” (for some reason it treated the symbols as html tags or something.
Click on the application, not on the window
I see, thanks. Thing is I wanted to get some info about an “untracked” app (I guess it’s some binary with a embedded icon), to see if I could change its icon (Mathematica 11 in this case).
And my main question out of all of this is…”Gnome Recipes”? This is the first I’ve heard of such a thing what’s the status, I can’t seem to find anything on it. I’ve been looking for a good replacement for Gourmet Recipe Manager, and have even considered starting a project myself, but it hasn’t been a priority.
Please, ~please~, share GNOME Recipes with the community.
> Restart GNOME shell (this is necessary due to a bug where GNOME shell will not reliably pick up desktop file changes)
Out of interest, is there a BZ# for this? I ran into it recently, and figured it out, but doing this is somewhat disruptive, so it would be very nice to have a more targeted way to apply changes from .desktop files.
why are the headerbar corners not rounded though?
no gtk release with the fix yet, I believe
GNOME Recipes, seriously? I want it and I want it now! I was thinking about writing such an app to fill the need. 😮