Tried in different configurations, seems that line cursor works fine.
> b) format detection - I try to detect the header line - and I expect this > line has the most length of all lines. I use a line with the same length as > the column's type info (data, border).
I looked at pspg source, and here's what I found (please correct me if some/all of my assumptions are wrong):
1. Input handling and format detection happens in table.c readfile().
2. There's some variables in DataDesc - maxx and maxbytes - that store the longest line seen so far. But they are re-updated on each new row, so the fact that header is shorter shouldn't affect them.
3. Expanded header detection is handled by is_expanded_header function. It has ei_minx and ei_maxx return pointers, but when it is used from readfile() these pointers are set to NULL in both cases - so header length is simply ignored.
The problem can be in translate_headline in bad desc->headline_size
> Did you test the wrapped format? It is working > > \pset format wrapped > \x > select * from pg_class;
There's no difference in outputs in wrapped format, so pspg behavior is also unaffected.
By the way, it seems that pspg recommends setting \pset border 2 anyway, so in vast majority of cases there should be no possibility of difference at all - proposed patch doesn't change output for \pset border 2 (because there's no sane way of making it look okay in presence of long fields anyway).
Although pspg prefers border 2, it is working for all configurations now.
I think your proposal is not good, because it is breaking consistency and if people want similar output, then they can use a wrapped format.
