bug#51011: [PATCH] sort: --debug: add warnings about radix and grouping chars

[Pádraig Brady]

On 09/10/2021 23:29, Paul Eggert wrote:
> On 10/9/21 5:00 AM, Pádraig Brady wrote:
> > On 09/10/2021 04:48, Paul Eggert wrote:
>
> > > 'sort' could determine the group sizes from the locale, and
> > > reject digit strings that are formatted improperly according to the
> > > group-size rules. (Not that I plan to write the code to do that....)
> >
> > Yes I agree that would be better, but not worth it I think
> > as there would still be ambiguity in what was a grouping char
> > and what was a field separator. Also that ambiguity would
> > now vary across locales.
>
> I don't see the ambiguity problem. The field separator is used to
> identify fields; once the fields are identified, the thousands
> separator, decimal point, etc. contribute to numeric comparison in the
> usual way. So it's OK (albeit confusing) for the field separator to be
> '.' or ',' or '-' or '0' or any another character that could be part of
> a number.
>
> For example, with 'sort -t 0 -k 2,2n', the digit 0 is not part of the
> numeric field that is compared, and there's no ambiguity about that even
> though 0 is allowed in numbers. The same idea applies to 'sort -t , -k
> 2,2n'.

Indeed. I dropped -t, from my later examples and confused myself.

Attached is the proposed change to add appropriate warnings in this area.
Examples now diagnosed are:

  $ printf '0,9\n1,a\n' | sort -nk1 --debug -t, -s
  sort: key 1 is numeric and spans multiple fields
  sort: field separator ‘,’ is treated as a group separator in numbers
  1,a
  _
  0,9
  ___

  $ printf '1,a\n0,9\n' | LC_ALL=fr_FR.utf8 sort -gk1 --debug -t, -s
  sort: key 1 is numeric and spans multiple fields
  sort: field separator ‘,’ is treated as a decimal point in numbers
  0,9
  ___
  1,a
  __

  $ printf '1.0\n0.9\n' | sort -s -k1,1g --debug
  sort: numbers use ‘.’ as a decimal point in this locale
  0.9
  ___
  1.0
  ___

  $ printf '1.0\n0.9\n' | LC_ALL=fr_FR.utf8 sort -s -k1,1g --debug
  sort: numbers use ‘,’ as a decimal point in this locale
  0.9
  _
  1.0
  _

cheers,
Pádraig

sort--debug-radix.patch
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