Re: Bugfix for utf-8 XTerm/MinTTY and (set-input-meta-mode t)

[Max Mikhanosha <max.mikhanosha@protonmail.com>]

On Wednesday, June 2nd, 2021 at 8:16 AM, Andreas Schwab <schwab@linux-m68k.org> wrote:

> > If META is t, Emacs will accept 8-bit input, and interpret the 8th
> > bit as the Meta modifier.
> >
> > +If META is 'encoded', Emacs will decode the input with accordance
> > +to current coding system, and then examine decoded input 8th bit
> > +and interpret it as the Meta modifier
>
> in accordance to

Updated per above. Feel free to do any farther changes to wording or coding style if
you going to merge it, or let me know if you'd like me to improve this in any way.

diff --git a/src/keyboard.c b/src/keyboard.c
index aa3448439b..01f154ec04 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -2249,7 +2249,11 @@ read_decoded_event_from_main_queue (struct timespec *end_time,
 		  int i;
 		  if (meta_key != 2)
 		    for (i = 0; i < n; i++)
-		      events[i] = make_number (XINT (events[i]) & ~0x80);
+		      {
+			int c = XINT (events[i]);
+			int modifier = (meta_key == 3 && c < 0x100 && (c & 0x80)) ? meta_modifier : 0;
+			events[i] = make_number ((c & ~0x80) | modifier);
+		      }
 		}
 	      else
 		{
@@ -2258,7 +2262,7 @@ read_decoded_event_from_main_queue (struct timespec *end_time,
 		  int i;
 		  for (i = 0; i < n; i++)
 		    src[i] = XINT (events[i]);
-		  if (meta_key != 2)
+		  if (meta_key < 2) /* input-meta-mode T or NIL */
 		    for (i = 0; i < n; i++)
 		      src[i] &= ~0x80;
 		  coding->destination = dest;
@@ -2276,7 +2280,15 @@ read_decoded_event_from_main_queue (struct timespec *end_time,
 		      eassert (coding->carryover_bytes == 0);
 		      n = 0;
 		      while (n < coding->produced_char)
-			events[n++] = make_number (STRING_CHAR_ADVANCE (p));
+			{
+			  int c = STRING_CHAR_ADVANCE (p);
+			  if (meta_key == 3)
+			    {
+			      int modifier = (c < 0x100 && (c & 0x80)) ? meta_modifier : 0;
+			      c = (c & ~0x80) | modifier;
+			    }
+			  events[n++] = make_number (c);
+			}
 		    }
 		}
 	    }
@@ -7126,7 +7138,7 @@ tty_read_avail_input (struct terminal *terminal,
       buf.modifiers = 0;
       if (tty->meta_key == 1 && (cbuf[i] & 0x80))
         buf.modifiers = meta_modifier;
-      if (tty->meta_key != 2)
+      if (tty->meta_key < 2)
         cbuf[i] &= ~0x80;

       buf.code = cbuf[i];
@@ -10644,6 +10656,10 @@ DEFUN ("set-input-meta-mode", Fset_input_meta_mode, Sset_input_meta_mode, 1, 2,
 If META is t, Emacs will accept 8-bit input, and interpret the 8th
 bit as the Meta modifier.

+If META is 'encoded', Emacs will decode the input in accordance
+to current coding system, and then examine decoded input 8th bit
+and interpret it as the Meta modifier
+
 If META is nil, Emacs will ignore the top bit, on the assumption it is
 parity.

@@ -10671,8 +10687,10 @@ See also `current-input-mode'.  */)
     new_meta = 0;
   else if (EQ (meta, Qt))
     new_meta = 1;
-  else
+  else if (!EQ (meta, Qencoded))
     new_meta = 2;
+  else
+    new_meta = 3;

   if (tty->meta_key != new_meta)
     {
@@ -10754,6 +10772,7 @@ The value is a list of the form (INTERRUPT FLOW META QUIT), where
   FLOW is non-nil if Emacs uses ^S/^Q flow control for output to the
     terminal; this does not apply if Emacs uses interrupt-driven input.
   META is t if accepting 8-bit input with 8th bit as Meta flag.
+    META 'encoded' means the same but 8th bit is checked after coding system
     META nil means ignoring the top bit, on the assumption it is parity.
     META is neither t nor nil if accepting 8-bit input and using
     all 8 bits as the character code.
@@ -10771,7 +10790,8 @@ The elements of this list correspond to the arguments of
       flow = FRAME_TTY (sf)->flow_control ? Qt : Qnil;
       meta = (FRAME_TTY (sf)->meta_key == 2
 	      ? make_number (0)
-	      : (CURTTY ()->meta_key == 1 ? Qt : Qnil));
+	      : (CURTTY ()->meta_key == 1 ? Qt :
+		 (CURTTY ()->meta_key == 3 ? Qencoded : Qnil)));
     }
   else
     {
@@ -11210,6 +11230,9 @@ syms_of_keyboard (void)

   DEFSYM (Qecho_keystrokes, "echo-keystrokes");

+  /* input-meta-mode constant */
+  DEFSYM (Qencoded, "encoded");
+
   Fset (Qinput_method_exit_on_first_char, Qnil);
   Fset (Qinput_method_use_echo_area, Qnil);