Don't clobber docstrings of explicitly-defined mode hook variables

* lisp/emacs-lisp/derived.el (define-derived-mode):
* lisp/emacs-lisp/easy-mmode.el (define-minor-mode): When defining the
mode hook variable, do not clobber pre-existing docstrings.

2 files changed, 10 insertions, 6 deletions

diff --git a/lisp/emacs-lisp/derived.el b/lisp/emacs-lisp/derived.el
index 3fa3818526c..751291afa88 100644
--- a/lisp/emacs-lisp/derived.el
+++ b/lisp/emacs-lisp/derived.el
@@ -203,11 +203,13 @@ See Info node `(elisp)Derived Modes' for more details."
                      parent child docstring syntax abbrev))
 
     `(progn
-       (defvar ,hook nil
-         ,(format "Hook run after entering %s mode.
+       (defvar ,hook nil)
+       (unless (get ',hook 'variable-documentation)
+         (put ',hook 'variable-documentation
+              ,(format "Hook run after entering %s mode.
 No problems result if this variable is not bound.
 `add-hook' automatically binds it.  (This is true for all hook variables.)"
-                  name))
+                       name)))
        (unless (boundp ',map)
          (put ',map 'definition-name ',child))
        (with-no-warnings (defvar ,map (make-sparse-keymap)))
diff --git a/lisp/emacs-lisp/easy-mmode.el b/lisp/emacs-lisp/easy-mmode.el
index bf087fc2e9a..ac8dcc69d21 100644
--- a/lisp/emacs-lisp/easy-mmode.el
+++ b/lisp/emacs-lisp/easy-mmode.el
@@ -309,11 +309,13 @@ the mode if ARG is omitted or nil, and toggle it if ARG is `toggle'.
        ;; up-to-here.
        :autoload-end
 
-       (defvar ,hook nil
-         ,(format "Hook run after entering or leaving `%s'.
+       (defvar ,hook nil)
+       (unless (get ',hook 'variable-documentation)
+         (put ',hook 'variable-documentation
+              ,(format "Hook run after entering or leaving `%s'.
 No problems result if this variable is not bound.
 `add-hook' automatically binds it.  (This is true for all hook variables.)"
-                  modefun))
+                       modefun)))
 
        ;; Define the minor-mode keymap.
        ,(unless (symbolp keymap)        ;nil is also a symbol.