Inhibit null-string composition component (Bug#6988).

4 files changed, 26 insertions, 6 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index ad25d537f2b..2ee709f62b2 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2012-02-01  Kenichi Handa  <handa@m17n.org>
+
+        * composite.el (compose-region, compose-string): Signal error for
+        a null string component (Bug#6988).
+
 2012-01-31  Chong Yidong  <cyd@gnu.org>
 
         * frame.el (set-frame-font): New arg ALL-FRAMES.
diff --git a/lisp/composite.el b/lisp/composite.el
index 72317ac470e..739ec8bbcbd 100644
--- a/lisp/composite.el
+++ b/lisp/composite.el
@@ -211,7 +211,7 @@ or a vector or list of integers and rules.
 If it is a character, it is an alternate character to display instead
 of the text in the region.
 
-If it is a string, the elements are alternate characters.  In
+If it is a string, the elements are one or more alternate characters.  In
 this case, TAB element has a special meaning.  If the first
 character is TAB, the glyphs are displayed with left padding space
 so that no pixel overlaps with the previous column.  If the last
@@ -234,7 +234,9 @@ text in the composition."
   (let ((modified-p (buffer-modified-p))
         (inhibit-read-only t))
     (if (or (vectorp components) (listp components))
-        (setq components (encode-composition-components components)))
+        (setq components (encode-composition-components components))
+      (if (= (length components) 0)
+          (error "Invalid composition component: %s" components)))
     (compose-region-internal start end components modification-func)
     (restore-buffer-modified-p modified-p)))
 
@@ -267,7 +269,9 @@ Optional 5th argument MODIFICATION-FUNC is a function to call to
 adjust the composition when it gets invalid because of a change of
 text in the composition."
   (if (or (vectorp components) (listp components))
-      (setq components (encode-composition-components components)))
+      (setq components (encode-composition-components components))
+    (if (= (length components) 0)
+        (error "Invalid composition component: %s" components)))
   (or start (setq start 0))
   (or end (setq end (length string)))
   (compose-string-internal string start end components modification-func)
diff --git a/src/ChangeLog b/src/ChangeLog
index d114f0897eb..c41202bcfee 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,10 @@
+2012-02-01  Kenichi Handa  <handa@m17n.org>
+
+        * xdisp.c (BUILD_COMPOSITE_GLYPH_STRING): Initialize first_s to
+        NULL (Bug#6988).
+        (x_produce_glyphs): If the component of a composition is a null
+        string, set it->pixel_width to 1 to avoid zero-width glyph.
+
 2012-01-31  Glenn Morris  <rgm@gnu.org>
 
         * nsterm.m (syms_of_nsterm) <x-toolkit-scroll-bars>:
diff --git a/src/xdisp.c b/src/xdisp.c
index c90184f4a4c..864517b950c 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -22738,7 +22738,7 @@ compute_overhangs_and_x (struct glyph_string *s, int x, int backward_p)
     ptrdiff_t cmp_id = (row)->glyphs[area][START].u.cmp.id;                 \
     struct composition *cmp = composition_table[cmp_id];                    \
     XChar2b *char2b;                                                        \
-    struct glyph_string *first_s IF_LINT (= NULL);                          \
+    struct glyph_string *first_s = NULL;                                    \
     int n;                                                                  \
                                                                             \
     char2b = (XChar2b *) alloca ((sizeof *char2b) * cmp->glyph_len);        \
@@ -24400,7 +24400,7 @@ x_produce_glyphs (struct it *it)
           /* Initialize the bounding box.  */
           if (pcm)
             {
-              width = pcm->width;
+              width = cmp->glyph_len > 0 ? pcm->width : 0;
               ascent = pcm->ascent;
               descent = pcm->descent;
               lbearing = pcm->lbearing;
@@ -24408,7 +24408,7 @@ x_produce_glyphs (struct it *it)
             }
           else
             {
-              width = font->space_width;
+              width = cmp->glyph_len > 0 ? font->space_width : 0;
               ascent = FONT_BASE (font);
               descent = FONT_DESCENT (font);
               lbearing = 0;
@@ -24595,6 +24595,10 @@ x_produce_glyphs (struct it *it)
         it->glyph_row->contains_overlapping_glyphs_p = 1;
 
       it->pixel_width = cmp->pixel_width;
+      if (it->pixel_width == 0)
+        /* We assure that all visible glyphs have at least 1-pixel
+           width.  */
+        it->pixel_width = 1;
       it->ascent = it->phys_ascent = cmp->ascent;
       it->descent = it->phys_descent = cmp->descent;
       if (face->box != FACE_NO_BOX)