User .XCompose file not loaded

[crater2150]

Describe the bug
Compose sequences defined in my user compose file (~/.XCompose) do not work in kitty for me. Other programs (e.g. my browser) recognize them. I tried with the following minimal ~/.XCompose, which should insert an α when typing Compose, *, a:

<Multi_key> <asterisk> <a>      : "α"  U03B1       # GREEK SMALL LETTER ALPHA

Compose sequences defined in the locale's XCompose on the other hand do work, e.g. Compose, s, s inserts ß.

I tried with kitty 0.21.1 from Voidlinux and current master built from git.

To Reproduce
Steps to reproduce the behavior:

1. Create above compose file in ~/.XCompose
2. Run kitty (I used kitty --debug-keyboard --config NONE
3. Press Compose, *, a
4. Kitty shows *a instead of α

Environment details

kitty 0.21.2 (3a322c5c6e) created by Kovid Goyal
Linux deskhorst 5.12.14_1 #1 SMP 1625102948 x86_64
Void \r (\n) (\l)
Running under:X11

Config options different from defaults:

Additional context
Output from kitty --debug-keyboard on launch:

Loading new XKB keymaps
Modifier indices alt: 0x3 super: 0x6 hyper: 0xffffffff meta: 0xffffffff numlock: 0x4 shift: 0x0 capslock: 0x1

Output from kitty --debug-keyboard, when typing Compose, s, s (working case, locale XCompose, outputs ß):

Press xkb_keycode: 0x5e clean_sym: Multi_key compose not complete, ignoring.
Release xkb_keycode: 0x5e clean_sym: Multi_key mods: none glfw_key: 0 (UNKNOWN) xkb_key: 65312 (Multi_key) alternate_key: 60 (<)
on_key_input: glfw key: 0x0 native_code: 0xff20 action: RELEASE mods: none text: '' state: 0 ignoring release event for previous press that was handled as shortcut
Press xkb_keycode: 0x27 clean_sym: s compose not complete, ignoring.
Release xkb_keycode: 0x27 clean_sym: s mods: none glfw_key: 115 (s) xkb_key: 115 (s)
Press xkb_keycode: 0x27 clean_sym: s composed_sym: ssharp composed_text: ß mods: none glfw_key: 223 (ß) xkb_key: 223 (ssharp) shifted_key: 115 (s) alternate_key: 115 (s)
on_key_input: glfw key: 0xdf native_code: 0xdf action: PRESS mods: none text: 'ß' state: 0 sent text to child
Release xkb_keycode: 0x27 clean_sym: s mods: none glfw_key: 115 (s) xkb_key: 115 (s)

Output from kitty --debug-keyboard, when typing Compose, *, a (non-working case, user XCompose, outputs *a):

Press xkb_keycode: 0x5e clean_sym: Multi_key compose not complete, ignoring.
Release xkb_keycode: 0x5e clean_sym: Multi_key mods: none glfw_key: 0 (UNKNOWN) xkb_key: 65312 (Multi_key) alternate_key: 60 (<)
on_key_input: glfw key: 0x0 native_code: 0xff20 action: RELEASE mods: none text: '' state: 0 ignoring release event for previous press that was handled as shortcut
Press xkb_keycode: 0x32 clean_sym: Shift_L composed_sym: Shift_L mods: none glfw_key: 57441 (LEFT_SHIFT) xkb_key: 65505 (Shift_L)
on_key_input: glfw key: 0xe061 native_code: 0xffe1 action: PRESS mods: none text: '' state: 0 ignoring as keyboard mode does not support encoding this event
Got XkbNewKeyboardNotify event with changes: key codes: 1 geometry: 1 device id: 0
Loading new XKB keymaps
Modifier indices alt: 0x3 super: 0x6 hyper: 0xffffffff meta: 0xffffffff numlock: 0x4 shift: 0x0 capslock: 0x1
Press xkb_keycode: 0x11 clean_sym: 8 composed_sym: asterisk text: * mods: shift glfw_key: 56 (8) xkb_key: 56 (8) shifted_key: 42 (*)
on_key_input: glfw key: 0x38 native_code: 0x38 action: PRESS mods: shift text: '*' state: 0 sent text to child
Release xkb_keycode: 0x11 clean_sym: 8 mods: shift glfw_key: 56 (8) xkb_key: 56 (8) shifted_key: 42 (*)
on_key_input: glfw key: 0x38 native_code: 0x38 action: RELEASE mods: shift text: '' state: 0 ignoring as keyboard mode does not support encoding this event
Got XkbNewKeyboardNotify event with changes: key codes: 1 geometry: 1 device id: 0
Loading new XKB keymaps
Modifier indices alt: 0x3 super: 0x6 hyper: 0xffffffff meta: 0xffffffff numlock: 0x4 shift: 0x0 capslock: 0x1
Release xkb_keycode: 0x32 clean_sym: Shift_L mods: none glfw_key: 57441 (LEFT_SHIFT) xkb_key: 65505 (Shift_L)
on_key_input: glfw key: 0xe061 native_code: 0xffe1 action: RELEASE mods: none text: '' state: 0 ignoring as keyboard mode does not support encoding this event
Press xkb_keycode: 0x26 clean_sym: a composed_sym: a text: a mods: none glfw_key: 97 (a) xkb_key: 97 (a)
on_key_input: glfw key: 0x61 native_code: 0x61 action: PRESS mods: none text: 'a' state: 0 sent text to child
Release xkb_keycode: 0x26 clean_sym: a mods: none glfw_key: 97 (a) xkb_key: 97 (a)

[kovidgoyal]

kitty uses libxkbcommon for loading compose files, you will need to ask
its maintainers why it doesn't like your ~/.XCompose If you run kitty
from another terminal you will likely see an error about it printed out.

[crater2150]

There is no error message regarding the compose file, if I just launch kitty without typing anything, there is no output besides

Loading new XKB keymaps
Modifier indices alt: 0x3 super: 0x6 hyper: 0xffffffff meta: 0xffffffff numlock: 0x4 shift: 0x0 capslock: 0x1

I don't think I have any other programs, which use libxkbcommon directly instead of through Qt/GTK, so I can't test, if they work. For anyone interested, I reported this as xkbcommon/libxkbcommon#254.