kitty keyboard protocol: AltGr+plus should produce a tilde, but produces a plus instead

[neurocyte]

On Linux with the DE keyboard layout the AltGr modifier is interpreted differently in Ghostty to Kitty.

Here is kitty's interpretation:

ENTER RELEASE 
CSI 13 ; 1 : 3 u

ISO_LEVEL3_SHIFT PRESS 
CSI 57453 u

~ PRESS ~
CSI 126 :  : 93 ;  ; 126 u
Alternate key: ] 

~ RELEASE 
CSI 126 :  : 93 ; 1 : 3 u
Alternate key: ] 

ISO_LEVEL3_SHIFT RELEASE 
CSI 57453 ; 1 : 3 u

And here is Ghostty:

ENTER RELEASE
CSI 13 ; 1 : 3 u

RIGHT_ALT PRESS
CSI 57449 u

+ PRESS ~
CSI 43 ;  ; 126 u

+ RELEASE
CSI 43 ; 1 : 3 u

RIGHT_ALT RELEASE
CSI 57449 ; 1 : 3 u

[neurocyte]

Foot is a little different, but much closer to kitty:

ENTER RELEASE 
CSI 13 ; 1 : 3 u

ISO_LEVEL3_SHIFT PRESS 
CSI 57453 ; 1 : 1 u

~ PRESS ~
CSI 126 :  : 43 ; 1 : 1 ; 126 u
Alternate key: + 

~ RELEASE 
CSI 126 :  : 43 ; 1 : 3 u
Alternate key: + 

ISO_LEVEL3_SHIFT RELEASE 
CSI 57453 ; 1 : 3 u

[mitchellh]

You said foot so I assume this is Linux. The input stacks across operating systems are dramatically different so that's an important detail. Can you confirm?

[mitchellh]

Also, can you share perhaps a picture of the keyboard layout and exactly which key you're pressing?

[neurocyte]

Yes, Linux.

On the german keyboard layout AltGr is the regular right Alt key and + is the key two keys to the right of P. It's ] (left square bracket) on a US keyboard.

Note: This behavior applies to all AltGr (aka ISO_LEVEL3_SHIFT) modified key presses. It's not just ~.

[neurocyte]

This shows all the AltGr modifyable keys on a german keyboard. They are the lower right symbols.

[mitchellh]

As a note, here is macOS with a German standard layout, which is completely different and Ghostty does much better here (but still not 100% correct).

Kitty

alt+RIGHT_ALT PRESS 
CSI 57449 ; 3 u

alt++ PRESS ~
CSI 43 :  : 93 ; 3 ; 126 u
Alternate key: ] 

alt++ RELEASE 
CSI 43 :  : 93 ; 3 : 3 u
Alternate key: ] 

RIGHT_ALT RELEASE 
CSI 57449 ; 1 : 3 u

Ghostty

alt+RIGHT_ALT PRESS
CSI 57449 ; 3 u

alt++ PRESS ~
CSI 43 ; 3 ; 126 u

alt++ RELEASE
CSI 43 ; 3 : 3 u

RIGHT_ALT RELEASE
CSI 57449 ; 1 : 3 u

[neurocyte]

Here are the inspector events. Doesn't look like there is any ISO_LEVEL3_SHIFT info, so I guess it's at a lower level?

[mitchellh]

I've confirmed this with Linux.

This is a bug in the sense that we aren't matching Kitty here (and there is the minor alternate key issue on macOS too). But, I kind of want to open a discussion with Kovid and ask if this is a bug more generally in the Kitty keyboard protocol one way or the other (whether it should match Linux on macOS or vice versa).

One of the benefits of the keyboard protocol is that it tries to avoid the input-stack-specific quirks and provide a cross-platform input layer on top. If there are different key codes being sent for the same logical action on macOS and Linux, that's pretty annoying.

cc @gpanders @rockorager What do you think?

[mitchellh]

Also, just for notes: I confirmed this isn't related -- on macOS -- to macos_option_as_alt. I didn't think it would be since that has a minimal effect on the Kitty protocol (primarily impacts the legacy protocol) but I just wanted to check to be sure. I verified with Kitty on this.

[gpanders]

One of the benefits of the keyboard protocol is that it tries to avoid the input-stack-specific quirks and provide a cross-platform input layer on top. If there are different key codes being sent for the same logical action on macOS and Linux, that's pretty annoying.

+1 to discussing with Kovid. This consistency is important both for terminal developers and for applications.

[rockorager]

+1 to discussing with Kovid. This consistency is important both for terminal developers and for applications.

I agree.

If I were to derive the encoding from my understanding of the protocol, the key is '+', the text is '~', and the alternate key is ']'. This would be unmodified because the AltGr was consumed to produce the text (similar to option key in mac).

So it should be CSI 43 : : 93 ; ; 126 u

EDIT: I can see a case for having this as alt-modified.