[XeTeX] problem with discretionary

[jfbu]

Hi,

the problem is already fixed at XeTeX 0.99996 but it shows
with 0.99992 (TL2015), I tried to browse the commit history
at sourceforge to check which commit fixed that,
but I am not familiar enough with the repository, and besides
it could have been fixed as a collateral and perhaps a test
file needs to be added. So here we go:

% succeeds with:
% This is XeTeX, Version 3.14159265-2.6-0.99996 (TeX Live 2016) (preloaded
% format=xetex 2017.2.16)

% fails with:
% This is XeTeX, Version 3.14159265-2.6-0.99992 (TeX Live 2015) (preloaded
% format=xetex)
% ! Improper discretionary list.
% <recently read> }
                 
% ;->\discretionary {\char `\;}
%                              {}{\char `\;}
% l.12 a;
%        b

\catcode`@ 11
\XeTeXinterchartokenstate=1
\newXeTeXintercharclass\french at punctthin 
\XeTeXcharclass `\; \french at punctthin
      \XeTeXinterchartoks 255 \french at punctthin = {\nobreak\thinspace}%
\catcode`;\active
\def;{\discretionary{\char`\;}{}{\char`\;}}
a;b
\bye
% Local variables:
% TeX-engine: xetex
% End:

as you see from the notation this originated in use of polyglossia+french

the problem depends on the contents of the {\nobreak\thinspace} data,
with other data it does not show.

don't be alarmed by my strange \discretionary, it is here for
demonstration, original differs a bit.

So my query is which version of XeTeX fixed that issue ? (was it fixed
at initial TL2016 ? I only have a mature TL2016)

Best,

Jean-François