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

25 Dec 2021

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On 24 Dec 2021, at 18:34, Thomas Savary via ntg-context  wrote:
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 ?
Firstly, you have an extra } in the example above.

Secondly, rules need to come inside a data section. Thus (untested):

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

Regards,
—
Bruce Horrocks
Hampshire, UK