Fix use of ':align-to' in 'wrap-prefix'

* src/dispextern.h (struct it): New flag 'align_visually_p'.
* src/xdisp.c (handle_line_prefix): Set the 'align_visually_p'
flag for 'wrap-prefix'.
(produce_stretch_glyph): If 'align_visually_p' flag is set, count
the :align-to offset from the beginning of the screen line, not
from BOL.  (Bug#71605)

* doc/lispref/display.texi (Truncation, Specified Space): Document
the special handling of ':align-to' in 'wrap-prefix'.

2 files changed, 13 insertions, 1 deletions

diff --git a/src/dispextern.h b/src/dispextern.h
index 85012130689..51dc354d37c 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -2629,6 +2629,11 @@ struct it
      the current row.  */
   bool_bf line_number_produced_p : 1;
 
+  /* If true, the :align-to argument should be counted relative to the
+     beginning of the screen line, not the logical line.  Used by
+     'wrap-prefix'.  */
+  bool_bf align_visually_p : 1;
+
   enum line_wrap_method line_wrap;
 
   /* The ID of the default face to use.  One of DEFAULT_FACE_ID,
diff --git a/src/xdisp.c b/src/xdisp.c
index 0148cd76ada..5987813cd28 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -24494,6 +24494,11 @@ handle_line_prefix (struct it *it)
       prefix = get_line_prefix_it_property (it, Qwrap_prefix);
       if (NILP (prefix))
         prefix = Vwrap_prefix;
+      /* Interpreting :align-to relative to the beginning of the logical
+         line effectively renders this feature unusable, so we make an
+         exception for this use of :align-to.  */
+      if (!NILP (prefix))
+        it->align_visually_p = true;
     }
   else
     {
@@ -31972,7 +31977,9 @@ produce_stretch_glyph (struct it *it)
            && calc_pixel_width_or_height (&tem, it, prop, font, true,
                                           &align_to))
     {
-      int x = it->current_x + it->continuation_lines_width;
+      int x = it->current_x + (it->align_visually_p
+                               ? 0
+                               : it->continuation_lines_width);
       int x0 = x;
       /* Adjust for line numbers, if needed.   */
       if (!NILP (Vdisplay_line_numbers) && it->line_number_produced_p)