feature/derived-mode-add-parents 1245ce40293 5/7: subr.el: Add multiple inheritance to `derived-mode-p`

[Stefan Monnier]

branch: feature/derived-mode-add-parents
commit 1245ce4029364da6294b026062063864c13f363c
Author: Stefan Monnier <monnier@iro.umontreal.ca>
Commit: Stefan Monnier <monnier@iro.umontreal.ca>

    subr.el: Add multiple inheritance to `derived-mode-p`
    
    Add the ability for a major mode to declare "extra parents" in
    addition to the one from which it inherits.
    
    * lisp/subr.el (derived-mode-add-parents): New function.
    (derived-mode-all-parents): Adjust accordingly.
---
 lisp/subr.el | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lisp/subr.el b/lisp/subr.el
index e5ea0351934..b000787a5d6 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -2709,8 +2709,8 @@ The returned list is not fresh, don't modify it.
                          (let ((alias (symbol-function mode)))
                            (and (symbolp alias) alias))))
              (parents (cons mode (if parent (funcall all-parents parent))))
-             (extras (get mode 'derived-mode-extra-parent)))
-        (put mode 'derived-mode-all-parents
+             (extras (get mode 'derived-mode-extra-parents)))
+        (put mode 'derived-mode--all-parents
              (if (null extras) ;; Common case.
                  parents
                (delete-dups