[Dev-luatex] keeping in sync with pdftex changes

Hans Hagen j.hagen at xs4all.nl
Mon Jan 11 17:09:38 CET 2021

On 1/11/2021 4:15 PM, Ulrike Fischer wrote:
> Am Mon, 11 Jan 2021 16:01:09 +0100 schrieb luigi scarso:
>> I don't like the idea that something wrong now suddenly becomes right ---
> Well I never understood why this is a fatal error.  Why does pdftex
> or luatex care in my example about the boxing level? The worst that
> can happen is that pdftex calculates a wrong link area, so a warning
> makes sense. But the pdf is valid and there is imho (like with
> duplicated or missing destination names) no real reason to stop
> alltogether.
If that is the new criterium for error or no error, then what about

   invalid node of type ... in discretionary

(where the machinery can just ignore that node)

Other examples are: tex doesn't always error on overflow (dimensions can 
cycle) so why not silently recover in all cases.  And do we really care 
if a file ends inside an if? Or why make "a non-empty hbox expected" in 
margin kerns an error? Actually it makes sense to just ignore unknown 
parameters (keys) to some pdf related commands (probabbly less 
conceptual tricky than ignoring bad nesting). Errors in virtual fonts 
also are candidates. Invalid major or minor versions can be warnings 
instead of errors and invalid steps in expansion can be clipped to 
sensible values as can stack over- and underflow. Where does it end (in 
an engine that is supposed to be stable).

One can argue that it's up to the programmer (Knuth for the core engine, 
Thanh for pdftex extensions) which is quite valid but then we also must 
stress that luatex isn't compatible with pdftex in all aspects.

So, I agree with Luigi that it is kind of dubious (unless we make most 
non fatal looking backend errors optional i.e. turn them warning when 
some flag is set). The tex core has sometimes 'recovery' warnings (after 
error help) but that's too much work (and still it would be an error).

Anyway, we will ponder it.


                                           Hans Hagen | PRAGMA ADE
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