after adding more than 1601 ligatures, I am unable to compile the features and I get the following error message. below 1601 ligatures, everything works fine and I am able to compile and export the font.
is there a solution for this? (I tried use extension kerning parameter, but it did not work)
Lookups can only have a certain size. There are some things you can do to avoid that limit like outing the ligatures into several lookups and using extension lookups to fit them in.
To have a subtable overflow in GSUB features is quite rare. Can you send me the file that I can find the best was to fit it in?
one question though, will reducing the name of ligature itself (the text that comes after by, so in this example is ‘xxxyyy’) make a difference as well?
Hyphens, underscores, etc. are part of the glyph name and glyph names are not used in the font file for OpenType features. So, all the glyph names that you write in the feature code are converted to glyph indices (glyph ids, numbers) in the exported font file. Thus, the length of names in feature code does not matter for the file size of the exported font file.
There is no way to tell a number of entries. The internal structure is more complicated and it depends on many different bits and pieces how the data is stored and compressed.