Fix and document display of glyphless characters.

 src/xdisp.c (set_cursor_from_row): Fix cursor positioning on
 zero-width characters.
 (syms_of_xdisp) <glyphless-char-display>: Doc fix.
 src/.gdbinit (pgx): Adapt to latest changes in `struct glyph'.
 src/w32term.c (x_draw_glyphless_glyph_string_foreground): Draw the
 box before drawing the glyphs inside it.
 src/dispextern.h (enum glyphless_display_method): Rename
 GLYPHLESS_DISPLAY_HEXA_CODE to GLYPHLESS_DISPLAY_HEX_CODE.  All
 users changed.
 src/term.c (append_glyphless_glyph, produce_glyphless_glyph): Fix
 comments.
 (produce_glyphless_glyph): Enclose "U+nnnn" and "empty box"
 whitespace in "[]", to simulate a box.  Don't use uninitialized
 variable `width'.
 lisp/international/characters.el (glyphless-char-display-control):
 Renamed from glyphless-char-control; all users changed.  Doc fix.
 Signal an error if display method is not one of the recognized
 symbols.
 doc/emacs/rmail.texi (Rmail Coding): Characters with no fonts are not
 necessarily displayed as empty boxes.
 doc/emacs/mule.texi (Language Environments, Fontsets): Characters with no
 fonts are not necessarily displayed as empty boxes.
 doc/emacs/display.texi (Text Display): Document display of glyphless
 characters.
 doc/lispref/display.texi (Usual Display): Characters with no fonts are not
 necessarily displayed as empty boxes.
 etc/NEWS: Document display of glyphless characters.

1 files changed, 18 insertions, 15 deletions

diff --git a/src/term.c b/src/term.c
index dbbdc03f190..71df92822ac 100644
--- a/src/term.c
+++ b/src/term.c
@@ -1850,9 +1850,9 @@ produce_composite_glyph (struct it *it)
 
 
 /* Append a glyph for a glyphless character to IT->glyph_row.  FACE_ID
-   is a face ID to be used for the glyph.  What actually appended are
-   glyphs of type CHAR_GLYPH of which characters are in STR
-   (it->nglyphs bytes).  */
+   is a face ID to be used for the glyph.  What is actually appended
+   are glyphs of type CHAR_GLYPH whose characters are in STR (which
+   comes from it->nglyphs bytes).  */
 
 static void
 append_glyphless_glyph (struct it *it, int face_id, char *str)
@@ -1923,7 +1923,7 @@ extern Lisp_Object Qglyphless_char;
 /* Produce glyphs for a glyphless character for iterator IT.
    IT->glyphless_method specifies which method to use for displaying
    the character.  See the description of enum
-   glyphless_display_method in dispextern.h for the detail.
+   glyphless_display_method in dispextern.h for the details.
 
    FOR_NO_FONT is nonzero if and only if this is for a character that
    is not supproted by the coding system of the terminal.  ACRONYM, if
@@ -1935,11 +1935,11 @@ static void
 produce_glyphless_glyph (struct it *it, int for_no_font, Lisp_Object acronym)
 {
   int face_id;
-  int width, len;
-  char buf[9], *str = "    ";
+  int len;
+  char buf[11], *str = "    ";
 
   /* Get a face ID for the glyph by utilizing a cache (the same way as
-     doen for `escape-glyph' in get_next_display_element).  */
+     done for `escape-glyph' in get_next_display_element).  */
   if (it->f == last_glyphless_glyph_frame
       && it->face_id == last_glyphless_glyph_face_id)
     {
@@ -1956,8 +1956,8 @@ produce_glyphless_glyph (struct it *it, int for_no_font, Lisp_Object acronym)
 
   if (it->glyphless_method == GLYPHLESS_DISPLAY_THIN_SPACE)
     {
-      /* As there's no way to produce a thin space, we produce
-         a space of canonical width..  */
+      /* As there's no way to produce a thin space, we produce a space
+         of canonical width.  */
       len = 1;
     }
   else if (it->glyphless_method == GLYPHLESS_DISPLAY_EMPTY_BOX)
@@ -1965,8 +1965,11 @@ produce_glyphless_glyph (struct it *it, int for_no_font, Lisp_Object acronym)
       len = CHAR_WIDTH (it->c);
       if (len == 0)
         len = 1;
-      else if (width > 4)
+      else if (len > 4)
         len = 4;
+      sprintf (buf, "[%.*s]", len, str);
+      len += 2;
+      str = buf;
     }
   else
     {
@@ -1983,11 +1986,11 @@ produce_glyphless_glyph (struct it *it, int for_no_font, Lisp_Object acronym)
         }
       else
         {
-          xassert (it->glyphless_method == GLYPHLESS_DISPLAY_HEXA_CODE);
-          len = (it->c < 0x100 ? sprintf (buf, "U+%02X", it->c)
-                 : it->c < 0x10000 ? sprintf (buf, "U+%04X", it->c)
-                 : it->c <= MAX_UNICODE_CHAR ? sprintf (buf, "U+%06X", it->c)
-                 : sprintf (buf, "E+%06X", it->c));
+          xassert (it->glyphless_method == GLYPHLESS_DISPLAY_HEX_CODE);
+          len = (it->c < 0x100 ? sprintf (buf, "[U+%02X]", it->c)
+                 : it->c < 0x10000 ? sprintf (buf, "[U+%04X]", it->c)
+                 : it->c <= MAX_UNICODE_CHAR ? sprintf (buf, "[U+%06X]", it->c)
+                 : sprintf (buf, "[E+%06X]", it->c));
         }
       str = buf;
     }