(derived-mode-merge-keymaps): Recursively merge prefix key submaps also.

1 files changed, 23 insertions, 1 deletions

diff --git a/lisp/derived.el b/lisp/derived.el
index f48156a1010..a1cfe8485f8 100644
--- a/lisp/derived.el
+++ b/lisp/derived.el
@@ -297,8 +297,30 @@ Always merge its parent into it, since the merge is non-destructive."
 
 (defun derived-mode-merge-keymaps (old new)
   "Merge an old keymap into a new one.
-The old keymap is set to be the cdr of the new one, so that there will
+The old keymap is set to be the last cdr of the new one, so that there will
 be automatic inheritance."
+  (let ((tail new))
+    ;; Scan the NEW map for prefix keys.
+    (while (consp tail)
+      (and (consp (car tail))
+           (let* ((key (vector (car (car tail))))
+                  (subnew (lookup-key new key))
+                  (subold (lookup-key old key)))
+             ;; If KEY is a prefix key in both OLD and NEW, merge them.
+             (and (keymapp subnew) (keymapp subold)
+                  (derived-mode-merge-keymaps subold subnew))))
+      (and (vectorp (car tail))
+           ;; Search a vector of ASCII char bindings for prefix keys.
+           (let ((i (1- (length (car tail)))))
+             (while (>= i 0)
+               (let* ((key (vector i))
+                      (subnew (lookup-key new key))
+                      (subold (lookup-key old key)))
+                 ;; If KEY is a prefix key in both OLD and NEW, merge them.
+                 (and (keymapp subnew) (keymapp subold)
+                      (derived-mode-merge-keymaps subold subnew)))
+               (setq i (1- i)))))
+      (setq tail (cdr tail))))
   (setcdr (nthcdr (1- (length new)) new) old))
 
 (defun derived-mode-merge-syntax-tables (old new)