emacs-28 d791cd5: Fix '(space :relative-width N)' display spec w/non-ASCII chars

[Eli Zaretskii]

branch: emacs-28
commit d791cd556d622accb935e4dd230023c485d1e07a
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Fix '(space :relative-width N)' display spec w/non-ASCII chars
    
    * src/xdisp.c (produce_stretch_glyph): Use the correct face for
    non-ASCII characters.  Support :relative-width display spec on
    Lisp strings, not just on buffer text.
---
 src/xdisp.c | 30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index 0316408..b3647f7 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -29810,7 +29810,7 @@ append_stretch_glyph (struct it *it, Lisp_Object object,
 #endif /* HAVE_WINDOW_SYSTEM */
 
 /* Produce a stretch glyph for iterator IT.  IT->object is the value
-   of the glyph property displayed.  The value must be a list
+   of the display property.  The value must be a list of the form
    `(space KEYWORD VALUE ...)' with the following KEYWORD/VALUE pairs
    being recognized:
 
@@ -29820,7 +29820,7 @@ append_stretch_glyph (struct it *it, Lisp_Object object,
 
    2. `:relative-width FACTOR' specifies that the width of the stretch
    should be computed from the width of the first character having the
-   `glyph' property, and should be FACTOR times that width.
+   `display' property, and should be FACTOR times that width.
 
    3. `:align-to HPOS' specifies that the space should be wide enough
    to reach HPOS, a value in canonical character units.
@@ -29832,7 +29832,7 @@ append_stretch_glyph (struct it *it, Lisp_Object object,
 
    5. `:relative-height FACTOR' specifies that the height of the
    stretch should be FACTOR times the height of the characters having
-   the glyph property.
+   the display property.
 
    Either none or exactly one of 4 or 5 must be present.
 
@@ -29853,10 +29853,11 @@ produce_stretch_glyph (struct it *it)
 #ifdef HAVE_WINDOW_SYSTEM
   int ascent = 0;
   bool zero_height_ok_p = false;
+  struct face *face;
 
   if (FRAME_WINDOW_P (it->f))
     {
-      struct face *face = FACE_FROM_ID (it->f, it->face_id);
+      face = FACE_FROM_ID (it->f, it->face_id);
       font = face->font ? face->font : FRAME_FONT (it->f);
       prepare_face_for_display (it->f, face);
     }
@@ -29877,14 +29878,27 @@ produce_stretch_glyph (struct it *it)
   else if (prop = Fplist_get (plist, QCrelative_width), NUMVAL (prop) > 0)
     {
       /* Relative width `:relative-width FACTOR' specified and valid.
-        Compute the width of the characters having the `glyph'
+        Compute the width of the characters having this `display'
         property.  */
       struct it it2;
-      unsigned char *p = BYTE_POS_ADDR (IT_BYTEPOS (*it));
+      Lisp_Object object = it->stack[it->sp - 1].string;
+      unsigned char *p = (STRINGP (object)
+                         ? SDATA (object) + IT_STRING_BYTEPOS (*it)
+                         : BYTE_POS_ADDR (IT_BYTEPOS (*it)));
+      bool multibyte_p =
+       STRINGP (object) ? STRING_MULTIBYTE (object) : it->multibyte_p;
 
       it2 = *it;
-      if (it->multibyte_p)
-       it2.c = it2.char_to_display = string_char_and_length (p, &it2.len);
+      if (multibyte_p)
+       {
+         it2.c = it2.char_to_display = string_char_and_length (p, &it2.len);
+#ifdef HAVE_WINDOW_SYSTEM
+         if (FRAME_WINDOW_P (it->f) && ! ASCII_CHAR_P (it2.c))
+           it2.face_id = FACE_FOR_CHAR (it->f, face, it2.c,
+                                        IT_CHARPOS (*it),
+                                        STRINGP (object)? object : Qnil);
+#endif
+       }
       else
        {
          it2.c = it2.char_to_display = *p, it2.len = 1;