[NTG-context] Contextual removal of some ligatures using fonts.handlers.otf.addfeature (LuaTeX 1.13.2)

24 Dec 2021

      Hello, dear list !

In order to fix a few bugs in some OpenType features included in EB Garamond font provided by 
Google Fonts, I am trying to remove some ligatures (erroneous in some contexts) with 
fonts.handlers.otf.addfeature.

I must be missing something, because I can't get it to work.

Here is a minimal —non working—example :-)
(The attempted removal (“f_i” → “fi” only before “o”) is of course irrelevant. I chose it just for the 
sole purpose of this test, to provide a simple example. What I am trying to achieve is more complex, 
with other ligatures.) 

fonts.handlers.otf.addfeature{
        name = "unfio",
        type = "chainsubstitution",
        lookups = {
            { type = "multiple",
            data = { [ "f_i" ] = { "f", "i" } }
            }
        }
        rules = {
            { after = { { "o" } },
            current = { { "f_i" } },
            lookups = { 1 } }
        }
    }
}

Could someone please explain to me what I did wrong ?

Thomas Savary
1 le Grand-Plessis
F-85340 L’Île-d’Olonne
Tél. 06 22 82 61 34
https://compo85.fr/