bug#7214: sort --debug maps large old-style field number to 0 in diagnostic

[Jim Meyering]

Pádraig Brady wrote:
> On 14/10/10 11:06, Jim Meyering wrote:
>> I noticed that using a field number of SIZE_MAX or larger makes --debug
>> give an invalid diagnostic:
>>
>>   $ :|_POSIX2_VERSION=199209 src/sort --debug +$(echo 2^64-1|bc).4 -1.2
>>   src/sort: using simple byte comparison
>>   src/sort: obsolescent key `+0 -2' used; consider `-k 1,2' instead
>>   src/sort: leading blanks are significant in key 1; consider also 
>> specifying `b'
>
> I'd nearly call that corner case a feature,
> as it informs you the passed count has been wrapped.
> I.E. the obsolete syntax has a 1-less narrower range
> and this is informing you of that fact.
>
> printf "1 2\n" | src/sort -sb --debug +$((2**32-1)) -1
> src/sort: using `en_IE.UTF-8' sorting rules
> src/sort: obsolescent key `+0 -1' used; consider `-k 1,1' instead
> 1 2
> _
>
>
> It does mean though, that overflows on the start field
> for obsolete syntax do sort the data, while overflows
> with the -k syntax do not. We could detect that for
> the old syntax, and map overflows to SIZE_MAX-1?
>
> I suppose we could also add a debug warning for when
> we do overflow, something along the lines of:
>
> $ src/sort -sb --debug -k$((2**32)) /dev/null
> src/sort: 4294967296 is too large, using 4294967295
>
> @@ -3882,6 +3882,8 @@ parse_field_count (char const *string, size_t *val, 
> char const *msgid)
>      case LONGINT_OVERFLOW:
>      case LONGINT_OVERFLOW | LONGINT_INVALID_SUFFIX_CHAR:
>        *val = SIZE_MAX;
> +      if (debug) /* Note --debug must come before keys to diagnose this.  */
> +        error (0, 0, _("%" PRIuMAX " is too large, using %zu"), n, *val);

That does sound like an improvement (that would require comment changes),
but considering it's only with an outrageously large field number
and when using obsolescent key-specifying syntax, it's probably
not worth the trouble.  But if you want to add the above, that's
fine, too.

Note however, that would not change the mapping from a
field number of exactly SIZE_MAX to "0" in the diagnostic.