I have managed to create a few ligatures in some font editing software such as birdfont. However after I have installed my font into windows and I load PhpStorm, I select my font with the ligatures I have created but PhpStorm can't seem to display them.
My question is, can I make ligatures for letter sequences like f u n c t i o n or c l a s s for example? These are non standard ligatures that don't come included with FiraCode but I would really like to be able to make ligatures for these sequences, I have made them externally but how do I get PhpStorm or any JetBrains software to recognize them?
The answer is yes! You can make extra ligatures inside of a font and jetbrains will render them without any extra configuration. See the response from Nikita Prokopov below.
https://github.com/tonsky/FiraCode/issues/341
I believe it requires using a font editor like Glyphs.app or FontForge for example, so you should be able to configure a ligature character sequence in the font and the corresponding character/glyph in the font and jetbrains will be able to support it out of the box.