bug#45748: 28.0.50; fit-frame-to-buffer ignores leading spaces

[Aaron Jensen]

On Sat, Jan 9, 2021 at 9:57 AM Aaron Jensen <aaronjensen@gmail.com> wrote:
>
> I believe the problem is with:
>
> (window-text-pixel-size nil t)
>
> The FROM of t causes window-text-pixel-size to ignore leading spaces.
> A TO of t, causes it to ignore trailing spaces. fit-frame-to-buffer
> passes both as t. This is hardcoded unless you use
> fit-frame-to-buffer-1
>
> I can't say if window-text-pixel-size is behaving as expected or not.

The problematic code appears to be here in window-text-pixel-size:

else if (EQ (from, Qt))
  {
    start = BEGV;
    bpos = BEGV_BYTE;
    while (bpos < ZV_BYTE)
      {
c = fetch_char_advance (&start, &bpos);
if (!(c == ' ' || c == '\t' || c == '\n' || c == '\r'))
  break;
      }
    while (bpos > BEGV_BYTE)
      {
dec_both (&start, &bpos);
c = FETCH_BYTE (bpos);
if (!(c == ' ' || c == '\t'))
  break;
      }
  }

The second loop looks like it's attempting to backtrack to the
beginning of the line, but FETCH_BYTE (bpos) after a dec_both returns
the same character that the first loop ended on. In other words, start
and bpos are not in sync, or the way that FETCH_BYTE works is
different. If I subtract 1 from bpos when calling FETCH_BYTE, it works
as expected.