Better Syntax Highlighting Sway Configuration Files

I have been delving into the nuts and bolts of the Sway window manager lately and especially its fork SwayFX which adds a little eye candy in the style of Hyprland.

This has led to lots of sway config file editing and hence trying to work out the best way in emacs to work with them.

By default a typical sway/config file has its own configuration format and emacs tries its best to figure out which best mode to use and settles on conf-space-mode. This is a basic starter mode for a config that is space separated and gives me a rudimentary level of highlighting, for example :

I would like indentation to be a little more intelligent and currently this mode applies an ever increasing indent but I shall figure that out at a later date.

I was generally not unhappy with conf-space-mode as it gave me a rudimentary keyword form of highlighting and typically as a sway configuration file doesn’t need to be particularly structured I wasn’t ever really indenting anyway, but lets see if I can improve the syntax highlighting.

The first port of call is list-packages and searching for sway:

sway - Communication with the Sway window manager
sway-lang-mode - Major mode for sway

Unfortunately both don’t suit my use case and in fact the second is for the sway programming language of which this is not!.

Well how about treesitter?, a big hard nope for this as well.

Next up is a little ace up my sleeve and one that continues to prove advantageous when working with the Sway tiling manager. It is the fact that SwayWM is a drop in replacement for i3wm. Well if the sway config files are of the same format as i3 config files then surely I can use some kind of i3 emacs mode? and so it proved to be the case!

i3wm-config-mode - Better syntax highlighting for i3wm's config file

Explicitly running this mode gives me:

Much nicer! and comes with the following auto-mode-alist definition:

("i3/config\\'" . i3wm-config-mode)

which of course requires a little adjustment to auto associate this new i3 mode with my sway files. I came up with the following:

(add-to-list 'auto-mode-alist '("/sway/.*config.*/" . i3wm-config-mode))
(add-to-list 'auto-mode-alist '("/sway/config\\'" . i3wm-config-mode))

It took me a little while to figure out the regex as there are a few subtleties, for example it is recommended to always use \\’ rather than $ to eliminate the confusion around new lines.

Note that I put an extra directory slash at the regex start to stop the mode being applied to any other potential directories that might end in sway which I feel might be a more common future occurrence than a config directory containing i3.