Re: Ctrl-[ ?

[Stefan Monnier <monnier@iro.umontreal.ca>]

> See also https://emacs.stackexchange.com/questions/17509 where I show
> some other possibility (tho in the context of `tab` vs `C-i` vs TAB, but
> which is exactly the same problem).

FWIW, the patch below introduces a much more clear separation between
C-i and TAB and other such things, by distinguishing "control modifier
plus a char" events from the 32 "ASCII control chars".

It introduces various questions about how to print and read
those control thingies in Elisp and in user interactions.

But at least, for a quick 30 seconds test, it seems to handle the
simple cases.


        Stefan


diff --git a/lisp/bindings.el b/lisp/bindings.el
index 36044ab65d..22af38aeef 100644
--- a/lisp/bindings.el
+++ b/lisp/bindings.el
@@ -822,7 +822,7 @@ right-char
 see."
   (interactive "^p")
   (if visual-order-cursor-movement
-      (dotimes (i (if (numberp n) (abs n) 1))
+      (dotimes (_ (if (numberp n) (abs n) 1))
 	(move-point-visually (if (and (numberp n) (< n 0)) -1 1)))
     (if (eq (current-bidi-paragraph-direction) 'left-to-right)
 	(forward-char n)
@@ -840,7 +840,7 @@ left-char
 see."
   (interactive "^p")
   (if visual-order-cursor-movement
-      (dotimes (i (if (numberp n) (abs n) 1))
+      (dotimes (_ (if (numberp n) (abs n) 1))
 	(move-point-visually (if (and (numberp n) (< n 0)) 1 -1)))
     (if (eq (current-bidi-paragraph-direction) 'left-to-right)
 	(backward-char n)
@@ -1430,6 +1430,14 @@ ctl-x-4-map
 (define-key special-event-map [sigusr1] 'ignore)
 (define-key special-event-map [sigusr2] 'ignore)
 
+;;;; For merge-ASCII-control-and-CTRL-modifier
+(dotimes (ascii-ctrl 32)
+  (let* ((PLAIN-ctrl (+ 64 ascii-ctrl (ash 1 26))))
+    (dolist (mod (list 0 (ash 1 27))) ;With or without meta
+      (dolist (off (list 0 32))             ;Upper and lowercase
+        (define-key function-key-map (vector (+ PLAIN-ctrl off mod))
+          (vector (+ ascii-ctrl mod)))))))
+
 ;; Don't look for autoload cookies in this file.
 ;; Local Variables:
 ;; no-update-autoloads: t
diff --git a/lisp/simple.el b/lisp/simple.el
index 35022efdf4..184927c928 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -8817,7 +8817,7 @@ event-apply-modifier
 LSHIFTBY is the numeric value of this modifier, in keyboard events.
 PREFIX is the string that represents this modifier in an event type symbol."
   (if (numberp event)
-      (cond ((eq symbol 'control)
+      (cond ((and (eq symbol 'control) merge-ASCII-control-and-CTRL-modifier)
 	     (if (<= 64 (upcase event) 95)
 		 (- (upcase event) 64)
 	       (logior (ash 1 lshiftby) event)))
diff --git a/src/keyboard.c b/src/keyboard.c
index 35557e226c..9c92a7ccfd 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -2009,7 +2009,7 @@ make_ctrl_char (int c)
   /* Save the upper bits here.  */
   int upper = c & ~0177;
 
-  if (! ASCII_CHAR_P (c))
+  if (! ASCII_CHAR_P (c) || !merge_ascii_control_and_ctrl_modifier)
     return c |= ctrl_modifier;
 
   c &= 0177;
@@ -11811,6 +11811,11 @@ This inhibits recording input events for the purposes of keyboard
 macros, dribble file, and `recent-keys'.
 Internal use only.  */);
 
+  DEFVAR_BOOL ("merge-ASCII-control-and-CTRL-modifier",
+               merge_ascii_control_and_ctrl_modifier,
+               doc: /* When non-nil, C-i is the same as TAB.  */);
+  merge_ascii_control_and_ctrl_modifier = false;
+
   pdumper_do_now_and_after_load (syms_of_keyboard_for_pdumper);
 }
 
diff --git a/src/keymap.c b/src/keymap.c
index 78cd7d2990..16afdefab0 100644
--- a/src/keymap.c
+++ b/src/keymap.c
@@ -2130,8 +2130,9 @@ push_key_description (EMACS_INT ch, char *p)
       c -= alt_modifier;
     }
   if ((c & ctrl_modifier) != 0
-      || (c2 < ' ' && c2 != 27 && c2 != '\t' && c2 != Ctl ('M'))
-      || tab_as_ci)
+      || (merge_ascii_control_and_ctrl_modifier
+          && ((c2 < ' ' && c2 != 27 && c2 != '\t' && c2 != Ctl ('M'))
+              || tab_as_ci)))
     {
       *p++ = 'C';
       *p++ = '-';
@@ -2169,11 +2170,7 @@ push_key_description (EMACS_INT ch, char *p)
 	  *p++ = 'S';
 	  *p++ = 'C';
 	}
-      else if (tab_as_ci)
-	{
-	  *p++ = 'i';
-	}
-      else if (c == '\t')
+      else if (c == '\t' && merge_ascii_control_and_ctrl_modifier)
 	{
 	  *p++ = 'T';
 	  *p++ = 'A';
@@ -2187,7 +2184,11 @@ push_key_description (EMACS_INT ch, char *p)
 	}
       else
 	{
-	  /* `C-' already added above.  */
+          if (!merge_ascii_control_and_ctrl_modifier)
+            {
+	      *p++ = '\\';
+	      *p++ = '^';
+            }
 	  if (c > 0 && c <= Ctl ('Z'))
 	    *p++ = c + 0140;
 	  else