[luatex] Bug in tex.linebreak ?

[Frank Mittelbach]

Am 10.03.16 um 09:51 schrieb Hans Hagen:
> On 3/9/2016 8:48 PM, Frank Mittelbach wrote:
>> I think I found a bug in tex.linebreak.
>>
>> Consider the following code
>>
>>
>> function prelinebreak (head, groupnode)  --- for pre_linebreak_filter
>>                                           --- for example
>>    local n,t
>>
>>    n, t = tex.linebreak(node.copy_list(head), {looseness = -1})
>>    print("looseness=" .. t.looseness)
>>    n, t = tex.linebreak(node.copy_list(head), {looseness = 0})
>>    print("looseness=" .. t.looseness)
>>
>>    return true
>>
>> end
>>
>> and pass it in head a long enough hlist so that looseness -1 actually
>> works. The second line breaking with looseness=0 reports the previous
>> looseness ... same happens if you have looseness=+2 or +1 or so
>>
>> it seems that tex.linebreak always reports the looseness of the previous
>> linebreak action in case you pass it a "0"
>
> it helps if you also set some more (either explicit or at the tex
> level), like:
>
>    looseness=1,
>    tolerance=4500,
>    pretolerance=100,
>    emergencystretch=655360

not sure I understand Hans, on the TeX they are set (once) -- are you 
saying one needs to set them as part of the params table for 
tex.linebreak as in

   { looseness = 0, tolerance = tex.tolerance ....

just re-providing to tex.linebreak what is already set on the TeX level?

my thoughts without having seen the internal code of tex.linebreak is 
that if looseness = 0 the value that is reported at the end is actually 
never set so retains whatever the last time was put there (which is not 
making a problem while it is always 0 but shows the wrong value once you 
ever set it to non-zero and later back

frank