bug#22637: 25.1.50; `mode-line` face `:height` incompatible with `scroll-conservatively 101`.

[Eli Zaretskii]

> Date:  Sat, 13 Feb 2016 19:40:34 -0800
> From:  Keith David Bershatsky <esq@lawlist.com>
> Cc:  22637@debbugs.gnu.org
> 
> In addition to the fix that you implemented yesterday near the section of 
> "optimization 3", another similar fix would be needed near the following 
> "recenter" section that affects cursor visibility when using isearch where 
> sometimes point is below the bottom of the screen and remains there 
> subsequent to redisplay.  I have not yet been able to figure out how to use 
> `cursor_row_fully_visible_p`, so I used something a little easier for me to 
> understand that basically tests the same thing (I think).
> 
> If I can come up with a small test that demonstrates the problem when 
> searching, I'll send over an example.  The following code, however, does seem 
> to fix the problem in all of my tests.

Please do come up with a test case.  I don't want to make any change
that doesn't have a test which fails before and succeeds after the
change.  Having such test cases allows us to make sure later changes
don't reintroduce the same bug.

>   /* Added a check/fix for a problem similar/same as bug #22637.  */
>   if (1 == try_window (window, it.current.pos, TRY_WINDOW_CHECK_MARGINS))
>     {
>       bool fully_p = false;
>       EMACS_INT posint = PT;
>       struct buffer *buf;
>       int x, y, rtop, rbot, rowh, vpos;
>       buf = XBUFFER (w->contents);
>       if ((posint >= CHARPOS (startp) && posint <= BUF_ZV (buf))
>           && CHARPOS (startp) >= BUF_BEGV (buf)
>           && CHARPOS (startp) <= BUF_ZV (buf)
>           && pos_visible_p (w, posint, &x, &y, &rtop, &rbot, &rowh, &vpos))
>         fully_p = !rtop && !rbot;
>       if (!fully_p)
>         {
> #ifdef GLYPH_DEBUG
>           debug_method_add (w, "!fully_p -- goto try_to_scroll");
> #endif
>           goto try_to_scroll;
>         }
>         else
>           {
> #ifdef GLYPH_DEBUG
>             debug_method_add (w, "fully_p -- goto done");
> #endif
>             goto done;
>           }

I don't think this is correct.  try_window is called in many more
places in the display engine, so if this problem is due to what it
does, the fix should be inside try_window, not in its callers.

But I could be wrong -- I need to see the problem to be sure.

Thanks.