Those flags are ignored on emacs-mac and on other platforms if running emacs 28+ with harfbuzz feature. In those cases, ligatures are handled without needing the extra configuration provided by those flags.
For ligatures to work, you must either have a recent enough version of emacs which will compose ligatures automatically, or use the font specific configurations.
Ligatures are handled without needing additional configuration. If this doesn't work, report a bug with your current version of emacs and the ligatures which aren't working.
This module includes configuration to compose combinations like =->= or =::= into prettier glyphs (called a ligature). Depending on the current version of emacs, this is implemented in two different ways :
- prettify-symbols-mode method :: this is the "legacy" method. It uses a font which haves the ligatures as separate unicode symbols, and using prettify-symbols-mode, =->=-like combinations are manually listed and replaced with the correct symbol. The mapping between =->=-like sequences and unicode values in the font are font-specific ; therefore =+fira=, =+iosevka=... files and specific fonts are necessary for it to work.
- composition-function-table method :: regexes are used to match all the usual sequences which are composed into ligatures. These regexes are passed to emacs directly, which asks Harfbuzz to shape it. Ligatures are obtained automatically depending on the capabilities of the font, and no font-specific configuration is necessary.
Emacs-mac port implements the /composition-function-table/ method in its code, nothing is necessary on Doom side ; otherwise, Doom implements the /composition-function-table/ for emacs 28+ built with Harfbuzz support, and the /prettify-symbols-mode/ method otherwise.
Even though harfbuzz has been included in emacs 27, there is currently a [[https://lists.gnu.org/archive/html/bug-gnu-emacs/2020-04/msg01121.html][bug (#40864)]] which prevents a safe usage of /composition-function-table/ method in emacs 27.
