Improvements for curved quotes on Linux consule

This should help Emacs work better out-of-the-box on Linux consoles,
which have only limited support for displaying Unicode characters.
Also, undo the recent change that caused text-quoting-style to
affect quote display on terminals, so that the two features are
independent.  See Alan Mackenzie in:
http://lists.gnu.org/archive/html/emacs-devel/2015-09/msg00244.html
Finally, add a style parameter to startup--setup-quote-display,
so that this function can also be invoked after startup, with
different styles depending on user preference at the time.
* configure.ac: Check for linux/kd.h header.
* doc/emacs/display.texi (Text Display): Document quote display.
* doc/lispref/display.texi (Active Display Table):
* etc/NEWS:
* lisp/startup.el (startup--setup-quote-display, command-line):
text-quoting-style no longer affects quote display.
* doc/lispref/frames.texi (Terminal Parameters): Fix typo.
* lisp/international/mule-util.el (char-displayable-p):
* lisp/startup.el (startup--setup-quote-display):
On a text terminal supporting glyph codes, use the reported
glyph codes instead of the terminal coding system, as this
is more accurate on the Linux console.
* lisp/startup.el (startup--setup-quote-display):
New optional arg STYLE.
* src/fontset.c (Finternal_char_font):
Report glyph codes for a text terminal, if they are available.
Currently this is supported only for the Linux console.
* src/termhooks.h (struct terminal): New member glyph-code-table.
* src/terminal.c [HAVE_LINUX_KD_H]: Include <errno.h>, <linux/kd.h>.
(calculate_glyph_code_table) [HAVE_LINUX_KD_H]: New function.
(terminal_glyph_code): New function.

1 files changed, 65 insertions, 1 deletions

diff --git a/src/terminal.c b/src/terminal.c
index b48d0623e12..15d74f4e812 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -28,6 +28,11 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "coding.h"
 #include "keyboard.h"
 
+#ifdef HAVE_LINUX_KD_H
+# include <errno.h>
+# include <linux/kd.h>
+#endif
+
 /* Chain of all terminals currently in use.  */
 struct terminal *terminal_list;
 
@@ -193,7 +198,7 @@ ins_del_lines (struct frame *f, int vpos, int n)
 }
 
 /* Return the terminal object specified by TERMINAL.  TERMINAL may
-   be a terminal object, a frame, or nil for the terminal device of
+”   be a terminal object, a frame, or nil for the terminal device of
    the current frame.  If TERMINAL is neither from the above or the
    resulting terminal object is deleted, return NULL.  */
 
@@ -526,6 +531,65 @@ selected frame's terminal).  */)
   return store_terminal_param (decode_live_terminal (terminal), parameter, value);
 }
 
+#if HAVE_LINUX_KD_H
+
+/* Compute the glyph code table for T.  */
+
+static void
+calculate_glyph_code_table (struct terminal *t)
+{
+  Lisp_Object glyphtab = Qt;
+  enum { initial_unipairs = 1000 };
+  int entry_ct = initial_unipairs;
+  struct unipair unipair_buffer[initial_unipairs];
+  struct unipair *entries = unipair_buffer;
+  struct unipair *alloced = 0;
+
+  while (true)
+    {
+      int fd = fileno (t->display_info.tty->output);
+      struct unimapdesc unimapdesc = { entry_ct, entries };
+      if (ioctl (fd, GIO_UNIMAP, &unimapdesc) == 0)
+	{
+	  glyphtab = Fmake_char_table (Qnil, make_number (-1));
+	  for (int i = 0; i < unimapdesc.entry_ct; i++)
+	    char_table_set (glyphtab, entries[i].unicode,
+			    make_number (entries[i].fontpos));
+	  break;
+	}
+      if (errno != ENOMEM)
+	break;
+      entry_ct = unimapdesc.entry_ct;
+      entries = alloced = xrealloc (alloced, entry_ct * sizeof *alloced);
+    }
+
+  xfree (alloced);
+  t->glyph_code_table = glyphtab;
+}
+#endif
+
+/* Return the glyph code in T of character CH, or -1 if CH does not
+   have a font position in T, or nil if T does not report glyph codes.  */
+
+Lisp_Object
+terminal_glyph_code (struct terminal *t, int ch)
+{
+#if HAVE_LINUX_KD_H
+  if (t->type == output_termcap)
+    {
+      /* As a hack, recompute the table when CH is the maximum
+	 character.  */
+      if (NILP (t->glyph_code_table) || ch == MAX_CHAR)
+	calculate_glyph_code_table (t);
+
+      if (! EQ (t->glyph_code_table, Qt))
+	return char_table_ref (t->glyph_code_table, ch);
+    }
+#endif
+
+  return Qnil;
+}
+
 /* Initial frame has no device-dependent output data, but has
    face cache which should be freed when the frame is deleted.  */