[NTG-context] Bidi-related register problem

24 Jan 2019

      Recent betas have introduced a bidi-related problem with register 
processing.

In the following example, compilation generates a recoverable error when 
register processing has to trim an entry to fit maxwidth. The error is:

luatex warning  > node filter: error: ...eXt/tex/texmf-context/tex/context/base/mkiv/typo-dub.lua:496: attempt to index local 'stacktop' (a nil value)

Removing the maxwidth constraint, or setting it to a much wider value, 
allows error-free compilation.

Without \setupdirections[bidi=on,method=two] there is no problem, but 
without it RTL texts are not handled properly. This is a recent change; 
bidi=global worked a few months ago. (I have not tried with LTR text in 
a default-RTL document).

    % macros=mkvi
    \defineregister[Mindex]
    \setupregister [Mindex]
                    [n=2,
                     maxwidth=4cm,
                     balance=no]

    \starttexdefinition unexpanded MIndex
       \dosinglegroupempty\doMIndex
    \stoptexdefinition

    \starttexdefinition unexpanded doMIndex #MARKER
       \def\Marker{#MARKER}%
       \dosinglegroupempty\doMIndexFull
    \stoptexdefinition

    \starttexdefinition doMIndexFull #ITEM
       \doifelse{#ITEM}{}
         {\expanded{\Mindex{\Marker}}}
         {\expanded{\Mindex{\Marker+#ITEM}}}
    \stoptexdefinition

    \setupdirections [bidi=on,method=two]

    \setupbodyfont   [libertinus,11pt]

    \starttext

    \startparagraph
       \MIndex{One}{Mairzy doats and dozy doats and liddle lamzy divey}

       \input jojomayer

    \stopparagraph

    \startparagraph
    סלאם שלום
    \stopparagraph

    \placeregister[Mindex]
    \stoptext

-- 
Rik Kabel