Fight for Your Hotkeys

20 Aug, 2022 · #dev #macos #xcode

Today I've been overhauling my Xcode setup, including hotkeys. When I attempted to assign ⌘ ⌃ D to the “Show code review” action, I got a warning that the operating system already uses this combination, hence it wouldn't work. I checked, and indeed it was used to show the definition of the selected word.

I navigated to the System Preferences > Keyboard > Shortcuts to reassign or disable this shortcut, but there was no such entry. Doh!

I felt like insisting on using this hotkey for the diff view in the Xcode, so I started digging. After some googling, I found a com.apple.symbolichotkeys.plist property list that holds a subset of system shortcuts.

Since plist files are binaries, it requires special tooling to inspect them. It can be Xcode or PlistBuddy cli utility.

sh
/usr/libexec/PlistBuddy -c "Print" ~/Library/Preferences/com.apple.symbolichotkeys.plist

The output was puzzling.

Dict {
    AppleSymbolicHotKeys = Dict {
        12 = Dict {
            enabled = true
            value = Dict {
                type = standard
                parameters = Array {
                    65535
                    122
                    8650752
                }
            }
        }
        21 = Dict {
            enabled = false
            value = Dict {
                type = standard
                parameters = Array {
                    56
                    28
                    1835008
                }
            }
        }
		// many more...
    }
}

Further investigation revealed that the entry of AppleSymbolicHotKeys dict contains:

key: an int identifier of an action performed on the provided keybinding.
Value struct:
- enabled: a bool flag that enables/disables a shortcut.
- type: no idea what it is, but I didn't care.
- parameters: an array that encodes a keybinding:
  - #1: ASCII code of the character (or 65535 for non-ASCII characters).
  - #2: the keyboard key code for the character.
  - #3: the sum of the codes of the modifier keys (⌘, ⌃, ⇧ and ⌥):

0: No modifier
1048576: Command
262144: Control
131072: Shift
524288: Option
393216: Shift + Control
655360: Shift + Option
1179648: Shift + Command
786432: Control + Option
1310720: Control + Command
1572864: Option + Command
917504: Shift + Control + Option
1441792: Shift + Control + Command
1703936: Shift + Option + Command
1835008: Control + Option + Command
1966080: Shift + Control + Option + Command

The following gist helps a lot with decoding parameters array.

I hoped that if I find the entry with the parameters set to Array {100 2 1310720} which corresponds to ⌘ ⌃ D hotkey and flip its enabled flag, it will do the trick. But nope, such entry didn't exist in this dict. Doh!

Apparently, this hotkey comes from somewhere else, and at this point, I was supposed to give up, but one more idea crossed my mind. What if it is possible to add the corresponding action id to this plist and disable it? All I need is an identifier of this action. It was the hardest part. I still have no idea where these identifiers come from, but there is only one place on the internet where I found the mapping: a forum post that is long gone but stored in the web archive. Someone posted a source of such plist with comments on what action corresponds to a specific id.

So after inspecting it very closely, I found something similar:

// Dictionary MouseOver - Command, Shift, E
70 = { enabled = 1; value = { parameters = ( 101, 2, 1179648 ); type = standard; }; };

And it was exactly what I was looking for. Running this command, I disabled the system shortcut.

sh
defaults write com.apple.symbolichotkeys AppleSymbolicHotKeys -dict-add 70 '<dict><key>enabled</key><false/></dict>'

The last note is that changes to this file don't apply immediately. It would require a restart. But there is a command that applies changes right here right now:

sh
/System/Library/PrivateFrameworks/SystemAdministration.framework/Resources/activateSettings -u

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