Re: keymap inheritance for non-sparse keymaps

[Stefan Monnier]

> You sent a patch to test for explicit-nil-binding in keymap elements,
> but it seems to be an uninterned symbol and nothing in the patch could
> ever store it in a keymap element.  Could I see the whole patch?

You saw the whole patch.  The only place where the `explicit-nil-binding'
is introduced is in `store_in_keymap' where we turn a nil binding
into an `explicit-nil-binding'.

> I tend to think that this issue is not very important, and not worth
> paying much price for.

I agree that it's not worth paying much price for, but the patch seems
simple enough and eliminates this special case of dense-keymaps not
doing inheritance properly.


        Stefan


--- keymap.c.~1.243.~   Fri Nov  2 18:29:29 2001
+++ keymap.c    Sat Nov  3 13:27:00 2001
@@ -103,6 +103,11 @@
 /* Which keymaps are reverse-stored in the cache.  */
 static Lisp_Object where_is_cache_keymaps;
 
+/* An Qexplicit_nil_binding in a dense keymap means that this is
+   an explicit nil binding which should shadow any parent binding.
+   It's only used internally.  */
+static Lisp_Object Qexplicit_nil_binding;
+
 static Lisp_Object store_in_keymap P_ ((Lisp_Object, Lisp_Object, 
Lisp_Object));
 static void fix_submap_inheritance P_ ((Lisp_Object, Lisp_Object, 
Lisp_Object));
 
@@ -579,9 +584,17 @@
            /* Character codes with modifiers
               are not included in a char-table.
               All character codes without modifiers are included.  */
-           if (NATNUMP (idx)
-               && (XFASTINT (idx) & CHAR_MODIFIER_MASK) == 0)
+           if (NATNUMP (idx) && (XFASTINT (idx) & CHAR_MODIFIER_MASK) == 0)
+             {
              val = Faref (binding, idx);
+               /* `nil' has a special meaning for char-tables, so
+                  we use something else to record an explicitly
+                  unbound entry.  */
+               if (NILP (val))
+                 val = Qunbound;
+               else if (EQ (val, Qexplicit_nil_binding))
+                 val = Qnil;
+             }
          }
 
        /* If we found a binding, clean it up and return it.  */
@@ -755,12 +768,13 @@
            /* Character codes with modifiers
               are not included in a char-table.
               All character codes without modifiers are included.  */
-           if (NATNUMP (idx)
-               && ! (XFASTINT (idx)
-                     & (CHAR_ALT | CHAR_SUPER | CHAR_HYPER
-                        | CHAR_SHIFT | CHAR_CTL | CHAR_META)))
+           if (NATNUMP (idx) && !(XFASTINT (idx) & CHAR_MODIFIER_MASK))
              {
-               Faset (elt, idx, def);
+               Faset (elt, idx,
+                      /* `nil' has a special meaning for char-tables, so
+                         we use something else to record an explicitly
+                         unbound entry.  */
+                      NILP (def) ? Qexplicit_nil_binding : def);
                return def;
              }
            insertion_point = tail;
@@ -3427,6 +3441,9 @@
 
   Qmenu_item = intern ("menu-item");
   staticpro (&Qmenu_item);
+
+  Qexplicit_nil_binding = Fmake_symbol (build_string ("explicit-nil-binding"));
+  staticpro (&Qexplicit_nil_binding);
 
   where_is_cache_keymaps = Qt;
   where_is_cache = Qnil;