[luatex] kerning/ligature callback problem with ltluatex

[Werner LEMBERG]

> It works as you expect with
> 
> \documentclass{article}
> \usepackage[OT1]{fontenc}
> \directlua{dofile('latex.lua')}
> 
> \begin{document}
> ffi
> \end{document}
> 
> which is, I guess, equivalent to your plain tex trial, using tfm
> fonts and "classic" tfm ligature data.
> 
> If you use OpenType fonts things appear to be different (not that
> the manual makes that clear:-)

Oooooh!  Thanks for this information.

I spent *two full days* to find out what's going on, walking over the
callback source code of `ltluatex` line by line, and I couldn't find
any hint why this would fail.  Ditto for the luatex source code, which
I inspected, too.  I also did a lot of internet research, completely
in vain.

That's *extremely* frustrating, sorry to say.  Why aren't there *any*
hints in either the 'luaotfload' or the 'ltluatex' documentation that
both the 'kerning' and the 'ligaturing' callbacks have zero influence
on both the kerning and the ligaturing of OTF fonts?[*]


    Werner


[*] In hindsight (but *only* in hindsight) I can see what's going on,
    and the 'luaotfload' manual explains it: it is necessary to
    activate 'mode=base' font handling (either font-wise or globally
    in `luaotfload.conf`).