character decorations such as bar/hat not showing

[daviehh]

Describe the bug
With some programming languages, it is common to see unicode characters such as characters with bar or hats, e.g. in julia

θ̂ = 1; θ̄ = 2; θ̂ - θ̄

To Reproduce
Steps to reproduce the behavior:

1. copy/paste the code above
2. (or, if you have julia repl, type in \theta tab \hat tab
3. hat/over bar not showing

Screenshots
See screenshot, both iterm(right) and kitty(left) configured to use FiraCode Nerd Font Mono

Environment details

kitty 0.31.0 (b247fda672) created by Kovid Goyal
Darwin david-MacbookPro.local 23.1.0 Darwin Kernel Version 23.1.0: Mon Oct  9 21:27:24 PDT 2023; root:xnu-10002.41.9~6/RELEASE_ARM64_T6000 arm64
ProductName:		macOS ProductVersion:		14.1.2 BuildVersion:		23B92
Frozen: True
Paths:
  kitty: /Applications/kitty.app/Contents/MacOS/kitty
  base dir: /Applications/kitty.app/Contents/Resources/kitty
  extensions dir: /Applications/kitty.app/Contents/Resources/Python/lib/kitty-extensions
  system shell: /opt/homebrew/bin/zsh
Loaded config files:
  /Users/david/.config/kitty/kitty.conf

Config options different from defaults:
bold_font                  FiraCode Nerd Font Mono
bold_italic_font           FiraCode Nerd Font Mono
copy_on_select             clipboard
cursor_blink_interval      0.9
cursor_shape               2
cursor_stop_blinking_after 0
font_family                FiraCode Nerd Font Mono
font_size                  12.0
italic_font                FiraCode Nerd Font Mono
tab_bar_edge               1
tab_bar_style              powerline
tab_powerline_style        round
Colors:
	active_border_color        #b7bdf8   
	active_tab_background      #c6a0f6   
	active_tab_foreground      #181926   
	background                 #24273a   
	bell_border_color          #eed49f   
	color0                     #494d64   
	color1                     #ed8796   
	color10                    #a6da95   
	color11                    #eed49f   
	color12                    #8aadf4   
	color13                    #f5bde6   
	color14                    #8bd5ca   
	color15                    #a5adcb   
	color2                     #a6da95   
	color3                     #eed49f   
	color4                     #8aadf4   
	color5                     #f5bde6   
	color6                     #8bd5ca   
	color7                     #b8c0e0   
	color8                     #5b6078   
	color9                     #ed8796   
	cursor                     #f4dbd6   
	cursor_text_color          #24273a   
	foreground                 #cad3f5   
	inactive_border_color      #6e738d   
	inactive_tab_background    #1e2030   
	inactive_tab_foreground    #cad3f5   
	mark1_background           #b7bdf8   
	mark1_foreground           #24273a   
	mark2_background           #c6a0f6   
	mark2_foreground           #24273a   
	mark3_background           #7dc4e4   
	mark3_foreground           #24273a   
	selection_background       #f4dbd6   
	selection_foreground       #24273a   
	tab_bar_background         #181926   
	url_color                  #f4dbd6   

Important environment variables seen by the kitty process:
	PATH                                /Applications/kitty.app/Contents/MacOS:/usr/bin:/bin:/usr/sbin:/sbin
	LANG                                en_US.UTF-8
	SHELL                               /opt/homebrew/bin/zsh
	USER                                david

Thanks!

[kovidgoyal]

this is something specific to macOS for whatever reason CoreText doesn't
seem to want to draw these specific combining chars as best as I can
tell. They render fine on my Linux system. Not sure what to do to
convince it to draw them. I will investigate in more depth when I have
some time.

[kovidgoyal]

Yeah we can see that its the combination of the theta and the combinging char. Probably because of the font the theta comes from. â renders correctly, but θ̂ does not. Sigh, more of my life burnt on reverse engineering apple's nonsense.

[kovidgoyal]

minimal reproducer:

kitty --hold --debug-font-fallback --config NONE kitty +runpy 'print("\u03b8\u0302 a\u0302")'

[kovidgoyal]

Issue seems to be with advances not being reset for glyphs to be rendered as a combined group. Even more minimal reproducer:

kitty --hold --config NONE kitty +runpy print("Q\u0302")

[daviehh]

thanks for the quick update!