master cd88f6de4b: Adjust zero-width grapheme clusters so they are displayed (Bug#50951)

[YAMAMOTO Mitsuharu]

branch: master
commit cd88f6de4be1f8eba1db038b371d769f584be53b
Author: YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>
Commit: YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>

    Adjust zero-width grapheme clusters so they are displayed (Bug#50951)
    
    * src/composite.c (composition_gstring_adjust_zero_width): New function.
    * src/composite.h: Declare it.
    * src/font.c (Ffont_shape_gstring): Use it before putting gstring to cache.
---
 src/composite.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 src/composite.h |  1 +
 src/font.c      |  1 +
 3 files changed, 46 insertions(+)

diff --git a/src/composite.c b/src/composite.c
index 249d7587f6..0417bc866d 100644
--- a/src/composite.c
+++ b/src/composite.c
@@ -800,6 +800,50 @@ composition_gstring_width (Lisp_Object gstring, ptrdiff_t 
from, ptrdiff_t to,
   return width;
 }
 
+/* Adjust the width of each grapheme cluster of GSTRING because
+   zero-width grapheme clusters are not displayed.  If the width is
+   zero, then the width of the last glyph in the cluster is
+   incremented.  */
+
+void
+composition_gstring_adjust_zero_width (Lisp_Object gstring)
+{
+  ptrdiff_t from = 0;
+  int width = 0;
+
+  for (ptrdiff_t i = 0; ; i++)
+    {
+      Lisp_Object glyph;
+
+      if (i == LGSTRING_GLYPH_LEN (gstring)
+         || (glyph = LGSTRING_GLYPH (gstring, i),
+             (NILP (glyph) || from != LGLYPH_FROM (glyph))))
+       {
+         eassert (i > 0);
+         Lisp_Object last = LGSTRING_GLYPH (gstring, i - 1);
+
+         if (width == 0)
+           {
+             if (NILP (LGLYPH_ADJUSTMENT (last)))
+               LGLYPH_SET_ADJUSTMENT (last,
+                                      CALLN (Fvector,
+                                             make_fixnum (0), make_fixnum (0),
+                                             make_fixnum (LGLYPH_WIDTH (last)
+                                                          + 1)));
+             else
+               ASET (LGLYPH_ADJUSTMENT (last), 2,
+                     make_fixnum (LGLYPH_WADJUST (last) + 1));
+           }
+         if (i == LGSTRING_GLYPH_LEN (gstring) || NILP (glyph))
+           break;
+         from = LGLYPH_FROM (glyph);
+         width = 0;
+       }
+      width += (NILP (LGLYPH_ADJUSTMENT (glyph))
+               ? LGLYPH_WIDTH (glyph) : LGLYPH_WADJUST (glyph));
+    }
+}
+
 
 static Lisp_Object gstring_work;
 static Lisp_Object gstring_work_headers;
diff --git a/src/composite.h b/src/composite.h
index d77dd0d506..8a6fd203d0 100644
--- a/src/composite.h
+++ b/src/composite.h
@@ -340,6 +340,7 @@ extern Lisp_Object composition_gstring_from_id (ptrdiff_t);
 extern bool composition_gstring_p (Lisp_Object);
 extern int composition_gstring_width (Lisp_Object, ptrdiff_t, ptrdiff_t,
                                       struct font_metrics *);
+extern void composition_gstring_adjust_zero_width (Lisp_Object);
 
 extern bool find_automatic_composition (ptrdiff_t, ptrdiff_t, ptrdiff_t,
                                        ptrdiff_t *, ptrdiff_t *,
diff --git a/src/font.c b/src/font.c
index 413cb381ee..defbb5084b 100644
--- a/src/font.c
+++ b/src/font.c
@@ -4678,6 +4678,7 @@ GSTRING.  */)
       from = LGLYPH_FROM (glyph);
       to = LGLYPH_TO (glyph);
     }
+  composition_gstring_adjust_zero_width (gstring);
   return composition_gstring_put_cache (gstring, XFIXNUM (n));
 
  shaper_error: