On 12/18/2015 10:27 PM, David Carlisle wrote:
The idiom
\mathchardef\foo=\mathcode`\x
is commonly used to save a mathcode of some character while you
temporarily change it for some reason.
Notably it's used (4 times) during the loading of the AMS package
amsmath, the main math support in latex.
this breaks in 0.87 as \mathcode returns a number suitable for
\Umathcharnumdef which is too large for \mathchardef.
I'm not (necessarily) suggesting that the luatex behaviour change but
if anyone is wanting to test latex math support with the new engine
they may want to patch a local copy of amsmath.sty for testing as at
the end of this message.
Since \mathchardef is mainly for legacy use anyway, I wonder if luatex
could keep this working, specifically \mathchardef if given a number
bigger than hex 8000 could perhaps (instead of giving an error) act
like \Umathcharnumdef.. An alternative would be to try to do the same
test via a macro redefinition of \mathchardef probably using the lua
token scanner to get the integer) but emulating all the primitive
behaviour in a compatible way might be hard.
changing the meaning of \mathchardef is also kind of incompatible (who
knows who depends on the error message for whatever reason)
anyway, i'll add that fallback but there is no way back and it will not
be under some 'option' control
Hans
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