[Dev-luatex] Recalculating tail of the list in ligaturing callback

Hans Hagen j.hagen at xs4all.nl
Wed Nov 14 14:14:36 CET 2018

On 11/14/2018 12:47 PM, Esger Renkema wrote:
> Dear list,
> Running the following one-liner:
> \directlua{callback.register('ligaturing', node.ligaturing)}ffi\bye
> results in:
> -------------------------------------------
> This is LuaTeX, Version 1.09.0 (TeX Live 2019/dev/Debian)
> restricted system commands enabled.
> **\directlua{callback.register('ligaturing', node.ligaturing)}ffi\bye
> ! error:  (linebreak): invalid list tail, probably missing glue
> !  ==> Fatal error occurred, no output PDF file produced!
> -------------------------------------------
> The problem seems to be that, when restoring the original ‘tail of the 
> list’ after applying the ligaturing callback (in this case consisting of 
> the parfillskip glue), it is appended to the tail of the /original/ 
> list-to-be-ligatured. The latter, of course, has been lost if the 
> paragraph ends in a ligature.

the user of a callback is responsible for returning the right result

you can locate the for your case proper end node and pass that one as 
second argument

> According to the manual, the first node of the list passed to the 
> callback is guaranteed not to be a glyph_node. Should the same not hold 
> for the last one, too? The manual states that it ‘normally’ is a glue, 
> but that is clearly not the case here.
contextual ligature building can be influences by glue nodes (i.e. 
spaces) so the whole list gets passed

we're not going to add overhead for checking the result


                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl

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