Add new user option 'translate-upper-case-key-bindings'

* doc/lispref/commands.texi (Key Sequence Input): Document it.

* lisp/cus-start.el (standard): defcustom it.

* src/keyboard.c (read_key_sequence): Use it.
(syms_of_keyboard): New variable 'translate-upper-case-key-bindings'.

1 files changed, 20 insertions, 7 deletions

diff --git a/src/keyboard.c b/src/keyboard.c
index bc6f97586dd..4f3232dc46c 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -10168,7 +10168,8 @@ read_key_sequence (Lisp_Object *keybuf, Lisp_Object prompt,
          use the corresponding lower-case letter instead.  */
       if (NILP (current_binding)
           && /* indec.start >= t && fkey.start >= t && */ keytran.start >= t
-          && FIXNUMP (key))
+          && FIXNUMP (key)
+          && translate_upper_case_key_bindings)
         {
           Lisp_Object new_key;
           EMACS_INT k = XFIXNUM (key);
@@ -10220,12 +10221,14 @@ read_key_sequence (Lisp_Object *keybuf, Lisp_Object prompt,
           int modifiers
             = CONSP (breakdown) ? (XFIXNUM (XCAR (XCDR (breakdown)))) : 0;
 
-          if (modifiers & shift_modifier
-              /* Treat uppercase keys as shifted.  */
-              || (FIXNUMP (key)
-                  && (KEY_TO_CHAR (key)
-                      < XCHAR_TABLE (BVAR (current_buffer, downcase_table))->header.size)
-                  && uppercasep (KEY_TO_CHAR (key))))
+          if (translate_upper_case_key_bindings
+              && (modifiers & shift_modifier
+                  /* Treat uppercase keys as shifted.  */
+                  || (FIXNUMP (key)
+                      && (KEY_TO_CHAR (key)
+                          < XCHAR_TABLE (BVAR (current_buffer,
+                                               downcase_table))->header.size)
+                      && uppercasep (KEY_TO_CHAR (key)))))
             {
               Lisp_Object new_key
                 = (modifiers & shift_modifier
@@ -12495,6 +12498,16 @@ If nil, Emacs crashes immediately in response to fatal signals.  */);
                Vwhile_no_input_ignore_events,
                doc: /* Ignored events from while-no-input.  */);
 
+  DEFVAR_BOOL ("translate-upper-case-key-bindings",
+               translate_upper_case_key_bindings,
+               doc: /* If non-nil, interpret upper case keys as lower case (when applicable).
+Emacs allows binding both upper and lower case key sequences to
+commands.  However, if there is a lower case key sequence bound to a
+command, and the user enters an upper case key sequence that is not
+bound to a command, Emacs will use the lower case binding.  Setting
+this variable to nil inhibits this behaviour.  */);
+  translate_upper_case_key_bindings = true;
+
   pdumper_do_now_and_after_load (syms_of_keyboard_for_pdumper);
 }