Re: [PATCH v3] blame: prevent error if range ends past end of file

[Isabella Stephens <istephens@atlassian.com>]

On 27/10/17 12:58 pm, Junio C Hamano wrote:
> Isabella Stephens <istephens@atlassian.com> writes:
> 
>> diff --git a/builtin/blame.c b/builtin/blame.c
>> index 67adaef4d..b5b9db147 100644
>> --- a/builtin/blame.c
>> +++ b/builtin/blame.c
>> @@ -878,13 +878,13 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
>>  				    nth_line_cb, &sb, lno, anchor,
>>  				    &bottom, &top, sb.path))
>>  			usage(blame_usage);
>> -		if (lno < top || ((lno || bottom) && lno < bottom))
>> +		if ((lno || bottom) && lno < bottom)
>>  			die(Q_("file %s has only %lu line",
>>  			       "file %s has only %lu lines",
>>  			       lno), path, lno);
>>  		if (bottom < 1)
>>  			bottom = 1;
>> -		if (top < 1)
>> +		if (top < 1 || lno < top)
>>  			top = lno;
> 
> This section sanity-checks first and then tweaks the values it
> allowed to pass the check.  Because it wants to later fix up an
> overly large "top" by capping to "lno" (i.e. total line number), the
> patch needs to loosen the early sanity-check.  And the "fixed up"
> values are never checked if they are sane.
> 
> For example, with an empty file (i.e. lno == 0), you can ask "git
> blame -L1,-4 ("i.e. "at most four lines, ending at line #1") and the
> code silently accepts the input without noticing that the request is
> an utter nonsense; "file X has only 0 lines" error is given a chance
> to kick in.
> 
> There should be an "is the range sensible?" check after all the
> tweaking to bottom and top are done, I think.

My mistake. I missed that case. I think this section of code is a little
hard to read because it avoids treating an empty file as a special case. 
Why not do something like this:

  for (range_i = 0; range_i < range_list.nr; ++range_i) {
          long bottom, top;
          if (!lno)
                  die(_("file is empty"));
          if (parse_range_arg(range_list.items[range_i].string,
                              nth_line_cb, &sb, lno, anchor,
                              &bottom, &top, sb.path))
                  usage(blame_usage);
          if (bottom < 1)
                  bottom = 1;
          if (lno < top)
                  top = lno;
          if (top < 0 || lno < bottom)
                   die(Q_("file %s has only %lu line",
                         "file %s has only %lu lines",
                         lno), path, lno);
          bottom--;
          range_set_append_unsafe(&ranges, bottom, top);
          anchor = top + 1;

We'd also need to change parse_range_arg to always make bottom less than top:

-       if (*begin && *end && *end < *begin) {
+       if (*end < *begin) {
                SWAP(*end, *begin);
        }

This also fixes the case where the given range is n,-(n+1) (e.g. -L1,-2). At
the moment that will blame from n to the end of the file. My suggested change
would instead blame the first n lines, which makes a lot more sense IMO.

Happy to leave as is if you aren't happy with this suggestion, however.