`C-SPC` bindings do not work on macOS as it conflicts with the input source switching shortcut

[skkzsh]

Problem

On macOS, Control + Space is reserved by the system as a shortcut for switching input sources (IME).
This affects users who type in languages that require an IME, such as Japanese, Chinese, and Korean.
Because this key combination is intercepted at the OS level, it never reaches Emacs, making all of Doom's C-SPC bindings inaccessible.

Affected bindings

Doom Emacs maps C-SPC in several places , including:

doomemacs/modules/completion/vertico/config.el

Line 46 in 4f4911f

"C-SPC" #'+vertico/embark-preview

doomemacs/modules/completion/vertico/config.el

Lines 141 to 145 in 4f4911f

	(consult-customize
	consult-ripgrep consult-git-grep consult-grep
	consult-bookmark consult-recent-file
	consult-source-recent-file consult-source-project-recent-file consult-source-bookmark
	:preview-key "C-SPC")

doomemacs/modules/lang/org/config.el

Line 965 in 4f4911f

:m "C-SPC" #'org-agenda-show-and-scroll-up

Question

Is there an officially recommended way to work around this conflict,
or would it be possible to provide an alternative default binding for macOS users?

As a stopgap, I found that adding the following to the config remaps another key to C-SPC:

(when (featurep :system 'macos)
  (keymap-set key-translation-map "C-:" [?\C-\ ])
  )

Steps to reproduce

1. On macOS, enable a CJK input source (e.g. Japanese, Chinese, or Korean) in System Settings → Keyboard → Input Sources.
2. Confirm that Control + Space is assigned as the input source switching shortcut in System Settings → Keyboard → Keyboard Shortcuts → Input Sources.
3. Open Doom Emacs and try pressing C-SPC (e.g. in a vertico buffer to preview).
4. The key combination is intercepted by macOS and never reaches Emacs.

System information

https://pastebin.com/D91vKSzA

Disclosures

• This issue was written with/by AI.

[4wardx]

IMO, you should use a different keybinding like C-S-SPC instead of C-SPC.
Mapping C-: to C-SPC isn't a great idea, as it will break other functions bound to this map.

[hlissner]

C-SPC is such a staple for code completion across text editors. What do other editors do about this on MacOS?

EDIT: Seems to be an known issue with VSCode and IntelliJ IDEs. A quick google search suggests most folks disable the input source shortcut.

[skkzsh]

IMO, you should use a different keybinding like C-S-SPC instead of C-SPC. Mapping C-: to C-SPC isn't a great idea, as it will break other functions bound to this map.

Thanks for the suggestion. I agree that remapping C-: to C-SPC is not a great solution.

EDIT: Is C-: already used for something, by the way?

C-S-SPC was actually one of the first alternatives I tried, but on macOS it does not seem to reach Emacs either, just like C-SPC. If I disable the macOS input source shortcut for C-SPC, then C-S-SPC starts working too, so it looks like the same OS-level interception is involved.

So I’m wondering if there’s a better alternative for macOS here.

EDIT: Seems to be an known issue with VSCode and IntelliJ IDEs. A quick google search suggests most folks disable the input source shortcut.

Thanks for the additional info. Oh, I see — that seems pretty inconvenient for macOS users with multiple input sources enabled, since C-SPC is still part of their day-to-day workflow.

So disabling the macOS shortcut entirely would affect the whole OS and other applications as well, and I’d prefer to find a solution that stays entirely on the Emacs side if possible.

[4wardx]

EDIT: Is C-: already used for something, by the way?

No, it seems to be free for now. However, remapping it like this messes with the global keymap logic.

Anyway, you can always manually bind any key to whatever you prefer, just be mindful of potential conflicts.