bug#77452: 31.0.50; Wide characters in left margin on ttys

[Eli Zaretskii]

> Cc: 77452@debbugs.gnu.org
> Date: Wed, 02 Apr 2025 17:47:47 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> 
> > I tried to read and understand display_line etc. this morning, but I'm 
> > afraid
> > there is too much going on there for me to find the cause of this in
> > reasonable time.
> 
> Does the below look right to you?

Sorry, please try the slightly more safe change below:

diff --git a/src/xdisp.c b/src/xdisp.c
index 2c676c0..33d7314 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -25685,7 +25685,7 @@ #define RECORD_MAX_MIN_POS(IT)                          
        \
 
       /* Now, get the metrics of what we want to display.  This also
         generates glyphs in `row' (which is IT->glyph_row).  */
-      n_glyphs_before = row->used[TEXT_AREA];
+      n_glyphs_before = row->used[it->area];
       x = it->current_x;
 
       /* Remember the line height so far in case the next element doesn't
@@ -25732,6 +25732,7 @@ #define RECORD_MAX_MIN_POS(IT)                          
        \
         the next one.  */
       if (it->area != TEXT_AREA)
        {
+         enum glyph_row_area area = it->area;
          row->ascent = max (row->ascent, it->max_ascent);
          row->height = max (row->height, it->max_ascent + it->max_descent);
          row->phys_ascent = max (row->phys_ascent, it->max_phys_ascent);
@@ -25740,6 +25741,15 @@ #define RECORD_MAX_MIN_POS(IT)                         
        \
          row->extra_line_spacing = max (row->extra_line_spacing,
                                         it->max_extra_line_spacing);
          set_iterator_to_next (it, true);
+         if (!FRAME_WINDOW_P (it->f)
+             /* If we exhausted the glyphs of the marginal area...      */
+             it->area != area
+             /* ...and the last character was multi-column...  */
+             && it->nglyphs > 1
+             /* ...and not all of its glyphs fit in the marginalk area... */
+             && row->used[area] < n_glyphs_before + it->nglyphs)
+             /* ...then reset back to the previous character.  */
+           row->used[area] = n_glyphs_before;
          /* If we didn't handle the line/wrap prefix above, and the
             call to set_iterator_to_next just switched to TEXT_AREA,
             process the prefix now.  */