refuse launching kitty-only kittens outside kitty

[RiedleroD]

Is your feature request related to a problem? Please describe.

I've gotten stuck in kitty's diff inside the tty a couple times because I forget that that doesn't work occasionally. Instead of just not launching, it doesn't recognize the exit keys, making me unable to exit the program so I have to open another tty just to kill the process.

Describe the solution you'd like
Making kitty diff exit when being launched outside a kitty environment would solve this problem. Same for any other kitten that makes you get stuck inside it.

Describe alternatives you've considered
Launching normal diff instead would also be a solution, but I feel like that'd be bad practice since people could start relying on that behaviour.

[kovidgoyal]

While kittens in general are designed to work only in kitty there is in
principle no reason they cannot work outside it. Your issue likely comes
from running it in a terminal emulator that does not support the kitty
keyboard protocol or inside a multiplexer that doesnt. I do not want to
artificially limit their usefulness to only kitty. Already several
terminal emulators support the protocol so hopefully this is a temporary
and fading issue.

[RiedleroD]

…yes, I was using the tty. Can we at least check if the current terminal supports the protocol and throw an error if it doesn't?

[kovidgoyal]

Sure, that's easy to do, feel free to send a PR relevant code is in
kittens/diff and how to detect support for the keyboard protocol is in
the spec at https://sw.kovidgoyal.net/kitty/graphics-protocol/#querying-support-and-available-transmission-mediums
You can add the query escape code to lp.OnInitialize and you will need
to add some code to parse the response escape codes, probably move that
into a method in Loop so other kittens can use it in the future.

When implementing it note that the kitten should not wait for the query
response, i.e. querying must not delay any processing, instead run
normally and when the response arrives exit or continue accordingly.

[kovidgoyal]

Sorry wrong spec link: https://sw.kovidgoyal.net/kitty/keyboard-protocol/#detection-of-support-for-this-protocol

[kovidgoyal]

Also remember to wait for the response before quitting the kitten if it hasnt arrived yet, otherwise the response could arrive at the shell as garbage.