bug#46422: [PATCH] Re: bug#46422: 'pr' screws up tabstops in multicolumn outpt?

[Leonard Janis Robert König]

Hi,

first:  Thank you very much for the work, I really owe you one!

On Sat, 2021-02-13 at 17:58 +0100, Erik Auerswald wrote:
> On 13.02.21 15:17, Erik Auerswald wrote:
> > On 11.02.21 20:20, Erik Auerswald wrote:
> > > On Thu, Feb 11, 2021 at 06:09:28PM +0100, Leonard Janis Robert
> > > König 
> > > wrote:
> > > > On Thu, 2021-02-11 at 16:45 +0100, Erik Auerswald wrote:
> > > > > On Thu, Feb 11, 2021 at 04:12:54PM +0100, Leonard Janis
> > > > > Robert
> > > > > König wrote:
> > > > > > On Thu, 2021-02-11 at 13:00 +0100, Erik Auerswald wrote:
> > > > > > > On Wed, Feb 10, 2021 at 01:42:29PM +0100, Leonard Janis
> > > > > > > Robert
> > > > > > > König wrote:
> > > > > > > > I'm sorry if I this is not a bug but to be expected,
> > > > > > > > but I thnk
> > > > > > > > pr doesn't get the alignment of tabs in multicolumn
> > > > > > > > output
> > > > > > > > right.  [...]  This seems *kind* of related to multi-
> > > > > > > > column
> > > > > > > > merged output, as was discussed some years ago here:
> > > > > > > > https://lists.gnu.org/archive/html/bug-coreutils/2007-03/msg00121.html
> > > > > > > >  
> > > > > > > > 
> > > > > > > 
> > > > > > > This thread contains the bug-introducing patch in message
> > > > > > > https://lists.gnu.org/archive/html/bug-coreutils/2007-03/msg00160.html
> > > > > > >  
> > > > > > > 
> > > > > > > 
> > > > > > > This is commit 553d347d3e08e00ee4f9df520b37c964c3f26e28.
> > > > > > 
> > > > > > ah, thanks for digging, I read the message but must have
> > > > > > missed
> > > > > > the patch.
> > > > > > 
> > > > > > > That commit removed the 'assume -e' part of the POSIX
> > > > > > > description
> > > > > > > of the -COLUMN option from GNU pr.
> > > > > > [...]
> > > > > Your test case requires expanding tabs during input, which is
> > > > > the reason that "expand | pr" could be used as a workaround
> > > > > (with
> > > > > "expand | pr | unexpand", pr would not need to mess with tabs
> > > > > at all,
> > > > > but I do think that GNU pr is currently buggy and should be
> > > > > fixed).
> > > > 
> > > > Absolutely, expand would be a workaround (I happen to use `pr -
> > > > e | pr`
> > > > in my script, for other reasons).
> > > > [...]
> > > I have found a fix to the problem described by you.  I am quite
> > > sure that
> > > this is not *correct*, but I did not find a way to make 
> > > print_sep_string()
> > > account for tabs that did not break quite a few existing tests,
> > > even if
> > > the merged files problem from 2007 and this columnating bug were
> > > both
> > > fixed.  Thus I just tighten the 2007 bug fix to apply in less
> > > cases.
> > > This way all existing tests pass, and a new one pertaining to
> > > this bug
> > > report passes, too.  I do think this is in the same spirit as the
> > > "fix"
> > > from 2007 (commit 553d347d3e08e00ee4f9df520b37c964c3f26e28).
> > 
> > I think the attached patch is a better fix than my previous one,
> > because it applies the special treatment of TAB as separator more
> > consistently.  It may still not be complete (the code seems quite
> > convoluted to me) but I do think it improves the situation
> > significantly, and does not make it worse.

Hm, I'm not sure whether I understand this special case.  When we have
a tab as column separator, doesn't this imply that the second column is
starting on a position n*8, (effectively equivalent to the first
column), thus guaranteeing that the alignment is honored?  So, if my
brain isn't completely off the track, with -s'\t' there shouldn't be a
difference whether we do -e -i or not, thus there needs not to be a
special case.

That being said, I don't see this exact distinction reflected in the
code, so perhaps I just misunderstood.

> 
> It seems to me as if "untabify_input = true;" should be re-introduced
> in one additional place to fix the regression from commit 553d347,
> please see the attached patch version 3.
> 
> > I'd like to ask the GNU Coreutils maintainers to consider merging
> > the attached patch.
> 
> The latest version, i.e., v3 for now.

I can only second this, with the patch my rather obscure (and complex)
use case of printing thousands of lines of code works properly now!

~leo