Fix rendering of composed caharacters on the mode line. (Bug#19435)

 src/xdisp.c (set_iterator_to_next) <GET_FROM_STRING>: Limit search in
 composition_compute_stop_pos to the number of characters in the
 string.
 <GET_FROM_BUFFER, GET_FROM_STRING>: Simplify code.
 src/composite.c (composition_compute_stop_pos): If no composition
 was found in a string before ENDPOS, and ENDPOS is the string end,
 no need to back up to a safe point.
 src/dispextern.h (struct it) <end_charpos>: Improve commentary.

4 files changed, 93 insertions, 99 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 2840109ac1c..2df83082fbd 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,16 @@
+2014-12-25  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (set_iterator_to_next) <GET_FROM_STRING>: Limit search in
+        composition_compute_stop_pos to the number of characters in the
+        string.  (Bug#19435)
+        <GET_FROM_BUFFER, GET_FROM_STRING>: Simplify code.
+
+        * composite.c (composition_compute_stop_pos): If no composition
+        was found in a string before ENDPOS, and ENDPOS is the string end,
+        no need to back up to a safe point.
+
+        * dispextern.h (struct it) <end_charpos>: Improve commentary.
+
 2014-12-24  Jan Djärv  <jan.h.d@swipnet.se>
 
         * nsimage.m (allocInitFromFile:): Initialize bmRep.
diff --git a/src/composite.c b/src/composite.c
index fa882141908..a1282103972 100644
--- a/src/composite.c
+++ b/src/composite.c
@@ -1036,7 +1036,8 @@ composition_compute_stop_pos (struct composition_it *cmp_it, ptrdiff_t charpos,
                 }
             }
         }
-      if (charpos == endpos)
+      if (charpos == endpos
+          && !(STRINGP (string) && endpos == SCHARS (string)))
         {
           /* We couldn't find a composition point before ENDPOS.  But,
              some character after ENDPOS may be composed with
diff --git a/src/dispextern.h b/src/dispextern.h
index 576f22870c2..0e5a73a929c 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -2222,7 +2222,10 @@ struct it
   ptrdiff_t base_level_stop;
 
   /* Maximum string or buffer position + 1.  ZV when iterating over
-     current_buffer.  */
+     current_buffer.  When iterating over a string in display_string,
+     this can be smaller or greater than the number of string
+     characters, depending on the values of PRECISION and FIELD_WIDTH
+     with which display_string was called.  */
   ptrdiff_t end_charpos;
 
   /* C string to iterate over.  Non-null means get characters from
diff --git a/src/xdisp.c b/src/xdisp.c
index e3e00357ed0..173df5d011b 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -7330,27 +7330,15 @@ set_iterator_to_next (struct it *it, int reseat_p)
       else if (it->cmp_it.id >= 0)
         {
           /* We are currently getting glyphs from a composition.  */
-          int i;
-
           if (! it->bidi_p)
             {
               IT_CHARPOS (*it) += it->cmp_it.nchars;
               IT_BYTEPOS (*it) += it->cmp_it.nbytes;
-              if (it->cmp_it.to < it->cmp_it.nglyphs)
-                {
-                  it->cmp_it.from = it->cmp_it.to;
-                }
-              else
-                {
-                  it->cmp_it.id = -1;
-                  composition_compute_stop_pos (&it->cmp_it, IT_CHARPOS (*it),
-                                                IT_BYTEPOS (*it),
-                                                it->end_charpos, Qnil);
-                }
             }
-          else if (! it->cmp_it.reversed_p)
+          else
             {
-              /* Composition created while scanning forward.  */
+              int i;
+
               /* Update IT's char/byte positions to point to the first
                  character of the next grapheme cluster, or to the
                  character visually after the current composition.  */
@@ -7358,52 +7346,34 @@ set_iterator_to_next (struct it *it, int reseat_p)
                 bidi_move_to_visually_next (&it->bidi_it);
               IT_BYTEPOS (*it) = it->bidi_it.bytepos;
               IT_CHARPOS (*it) = it->bidi_it.charpos;
+            }
 
-              if (it->cmp_it.to < it->cmp_it.nglyphs)
-                {
-                  /* Proceed to the next grapheme cluster.  */
-                  it->cmp_it.from = it->cmp_it.to;
-                }
-              else
-                {
-                  /* No more grapheme clusters in this composition.
-                     Find the next stop position.  */
-                  ptrdiff_t stop = it->end_charpos;
-                  if (it->bidi_it.scan_dir < 0)
-                    /* Now we are scanning backward and don't know
-                       where to stop.  */
-                    stop = -1;
-                  composition_compute_stop_pos (&it->cmp_it, IT_CHARPOS (*it),
-                                                IT_BYTEPOS (*it), stop, Qnil);
-                }
+          if ((! it->bidi_p || ! it->cmp_it.reversed_p)
+              && it->cmp_it.to < it->cmp_it.nglyphs)
+            {
+              /* Composition created while scanning forward.  Proceed
+                 to the next grapheme cluster.  */
+              it->cmp_it.from = it->cmp_it.to;
+            }
+          else if ((it->bidi_p && it->cmp_it.reversed_p)
+                   && it->cmp_it.from > 0)
+            {
+              /* Composition created while scanning backward.  Proceed
+                 to the previous grapheme cluster.  */
+              it->cmp_it.to = it->cmp_it.from;
             }
           else
             {
-              /* Composition created while scanning backward.  */
-              /* Update IT's char/byte positions to point to the last
-                 character of the previous grapheme cluster, or the
-                 character visually after the current composition.  */
-              for (i = 0; i < it->cmp_it.nchars; i++)
-                bidi_move_to_visually_next (&it->bidi_it);
-              IT_BYTEPOS (*it) = it->bidi_it.bytepos;
-              IT_CHARPOS (*it) = it->bidi_it.charpos;
-              if (it->cmp_it.from > 0)
-                {
-                  /* Proceed to the previous grapheme cluster.  */
-                  it->cmp_it.to = it->cmp_it.from;
-                }
-              else
-                {
-                  /* No more grapheme clusters in this composition.
-                     Find the next stop position.  */
-                  ptrdiff_t stop = it->end_charpos;
-                  if (it->bidi_it.scan_dir < 0)
-                    /* Now we are scanning backward and don't know
-                       where to stop.  */
-                    stop = -1;
-                  composition_compute_stop_pos (&it->cmp_it, IT_CHARPOS (*it),
-                                                IT_BYTEPOS (*it), stop, Qnil);
-                }
+              /* No more grapheme clusters in this composition.
+                 Find the next stop position.  */
+              ptrdiff_t stop = it->end_charpos;
+
+              if (it->bidi_it.scan_dir < 0)
+                /* Now we are scanning backward and don't know
+                   where to stop.  */
+                stop = -1;
+              composition_compute_stop_pos (&it->cmp_it, IT_CHARPOS (*it),
+                                            IT_BYTEPOS (*it), stop, Qnil);
             }
         }
       else
@@ -7532,61 +7502,63 @@ set_iterator_to_next (struct it *it, int reseat_p)
         }
       if (it->cmp_it.id >= 0)
         {
-          int i;
-
+          /* We are delivering display elements from a composition.
+             Update the string position past the grapheme cluster
+             we've just processed.  */
           if (! it->bidi_p)
             {
               IT_STRING_CHARPOS (*it) += it->cmp_it.nchars;
               IT_STRING_BYTEPOS (*it) += it->cmp_it.nbytes;
-              if (it->cmp_it.to < it->cmp_it.nglyphs)
-                it->cmp_it.from = it->cmp_it.to;
-              else
-                {
-                  it->cmp_it.id = -1;
-                  composition_compute_stop_pos (&it->cmp_it,
-                                                IT_STRING_CHARPOS (*it),
-                                                IT_STRING_BYTEPOS (*it),
-                                                it->end_charpos, it->string);
-                }
             }
-          else if (! it->cmp_it.reversed_p)
+          else
             {
+              int i;
+
               for (i = 0; i < it->cmp_it.nchars; i++)
                 bidi_move_to_visually_next (&it->bidi_it);
               IT_STRING_BYTEPOS (*it) = it->bidi_it.bytepos;
               IT_STRING_CHARPOS (*it) = it->bidi_it.charpos;
+            }
 
-              if (it->cmp_it.to < it->cmp_it.nglyphs)
-                it->cmp_it.from = it->cmp_it.to;
-              else
-                {
-                  ptrdiff_t stop = it->end_charpos;
-                  if (it->bidi_it.scan_dir < 0)
-                    stop = -1;
-                  composition_compute_stop_pos (&it->cmp_it,
-                                                IT_STRING_CHARPOS (*it),
-                                                IT_STRING_BYTEPOS (*it), stop,
-                                                it->string);
-                }
+          /* Did we exhaust all the grapheme clusters of this
+             composition?  */
+          if ((! it->bidi_p || ! it->cmp_it.reversed_p)
+              && (it->cmp_it.to < it->cmp_it.nglyphs))
+            {
+              /* Not all the grapheme clusters were processed yet;
+                 advance to the next cluster.  */
+              it->cmp_it.from = it->cmp_it.to;
+            }
+          else if ((it->bidi_p && it->cmp_it.reversed_p)
+                   && it->cmp_it.from > 0)
+            {
+              /* Likewise: advance to the next cluster, but going in
+                 the reverse direction.  */
+              it->cmp_it.to = it->cmp_it.from;
             }
           else
             {
-              for (i = 0; i < it->cmp_it.nchars; i++)
-                bidi_move_to_visually_next (&it->bidi_it);
-              IT_STRING_BYTEPOS (*it) = it->bidi_it.bytepos;
-              IT_STRING_CHARPOS (*it) = it->bidi_it.charpos;
-              if (it->cmp_it.from > 0)
-                it->cmp_it.to = it->cmp_it.from;
-              else
+              /* This composition was fully processed; find the next
+                 candidate place for checking for composed
+                 characters.  */
+              /* Always limit string searches to the string length;
+                 any padding spaces are not part of the string, and
+                 there cannot be any compositions in that padding.  */
+              ptrdiff_t stop = SCHARS (it->string);
+
+              if (it->bidi_p && it->bidi_it.scan_dir < 0)
+                stop = -1;
+              else if (it->end_charpos < stop)
                 {
-                  ptrdiff_t stop = it->end_charpos;
-                  if (it->bidi_it.scan_dir < 0)
-                    stop = -1;
-                  composition_compute_stop_pos (&it->cmp_it,
-                                                IT_STRING_CHARPOS (*it),
-                                                IT_STRING_BYTEPOS (*it), stop,
-                                                it->string);
+                  /* Cf. PRECISION in reseat_to_string: we might be
+                     limited in how many of the string characters we
+                     need to deliver.  */
+                  stop = it->end_charpos;
                 }
+              composition_compute_stop_pos (&it->cmp_it,
+                                            IT_STRING_CHARPOS (*it),
+                                            IT_STRING_BYTEPOS (*it), stop,
+                                            it->string);
             }
         }
       else
@@ -7609,12 +7581,17 @@ set_iterator_to_next (struct it *it, int reseat_p)
               bidi_move_to_visually_next (&it->bidi_it);
               IT_STRING_BYTEPOS (*it) = it->bidi_it.bytepos;
               IT_STRING_CHARPOS (*it) = it->bidi_it.charpos;
+              /* If the scan direction changes, we may need to update
+                 the place where to check for composed characters.  */
               if (prev_scan_dir != it->bidi_it.scan_dir)
                 {
-                  ptrdiff_t stop = it->end_charpos;
+                  ptrdiff_t stop = SCHARS (it->string);
 
                   if (it->bidi_it.scan_dir < 0)
                     stop = -1;
+                  else if (it->end_charpos < stop)
+                    stop = it->end_charpos;
+
                   composition_compute_stop_pos (&it->cmp_it,
                                                 IT_STRING_CHARPOS (*it),
                                                 IT_STRING_BYTEPOS (*it), stop,