additionally it supports a bookmark set per git branch which I get a lot of use out of

without plugin system is impossible, but would be a simple task to bundle it to the code, when i have time i will try and post the git patch here just i case someone else wants to try

Here is a simple harpoon implementation for tmux users.

Usage
Keymap is adjustable in helix:

• Ctrl+h:
  • Add current file:cursor_position to harpoon list
• Ctrl+jkl:
  • Switch to 1st, 2nd, or 3rd entry in the harpoon list.
• Ctrl+n:
  • Edit harpoon list on floating helix instance

Installation
Add these files to your path:
helix_harpoon_add
helix_harpoon_switch
helix_harpoon_edit
helix_harpoon_update
helix_harpoon_parse
You may need to adjust parsing regex if you have a customized status line.
I use this regex.

Add your harpoon bindings

[keys.normal]
"C-h" = ":pipe-to helix_harpoon_add"
"C-n" = ":pipe-to helix_harpoon_edit"
"C-j" = [":pipe-to helix_harpoon_update",":pipe-to helix_harpoon_switch 1"]
"C-k" = [":pipe-to helix_harpoon_update",":pipe-to helix_harpoon_switch 2"]
"C-l" = [":pipe-to helix_harpoon_update",":pipe-to helix_harpoon_switch 3"]
... # Expand as you need (4,5,6...).

Note: If you want to return where you were, using harpoon shortcuts; anything that changes your current buffer has to call helix_harpoon_update first. So, you must prepend it to all of these commands:

[keys.normal.g]
"n" = [":pipe-to helix_harpoon_update","goto_next_buffer"]
"p" = [":pipe-to helix_harpoon_update","goto_previous_buffer"]
"d" = [":pipe-to helix_harpoon_update","goto_definition"]
"y" = [":pipe-to helix_harpoon_update","goto_type_definition"]
"r" = [":pipe-to helix_harpoon_update","goto_reference"]
# There are more. Expand as you need.

Also, harpoon config is saved to $HOME/.cache/helix_harpoon/<pwd_hash>.txt