Make minor mode ARG work as documented

* lisp/emacs-lisp/easy-mmode.el (easy-mmode--arg-docstring):
Clarify when minor modes are switched on/off when called from lisp
(bug#44341).
(define-minor-mode): Make calls from Lisp switch the mode on/off
as documented.

2 files changed, 40 insertions, 9 deletions

diff --git a/lisp/emacs-lisp/easy-mmode.el b/lisp/emacs-lisp/easy-mmode.el
index a707d204f8b..a5a971a6981 100644
--- a/lisp/emacs-lisp/easy-mmode.el
+++ b/lisp/emacs-lisp/easy-mmode.el
@@ -84,10 +84,13 @@ replacing its case-insensitive matches with the literal string in LIGHTER."
 (defconst easy-mmode--arg-docstring
   "
 
-If called interactively, enable %s if ARG is positive, and
-disable it if ARG is zero or negative.  If called from Lisp,
-also enable the mode if ARG is omitted or nil, and toggle it
-if ARG is `toggle'; disable the mode otherwise.
+If called interactively, toggle `%s'.  If the prefix argument is
+positive, enable the mode, and if it is zero or negative, disable
+the mode.
+
+If called from Lisp, toggle the mode if if ARG is `toggle'.
+Enable the mode if ARG is nil, omitted, or is a positive number.
+All other values will disable the mode.
 
 The mode's hook is called both when the mode is enabled and when
 it is disabled.")
@@ -301,13 +304,20 @@ or call the function `%s'."))))
          ,(easy-mmode--mode-docstring doc pretty-name keymap-sym)
 	 ;; Use `toggle' rather than (if ,mode 0 1) so that using
 	 ;; repeat-command still does the toggling correctly.
-	 (interactive (list (or current-prefix-arg 'toggle)))
+	 (interactive (list (if current-prefix-arg
+                                (prefix-numeric-value current-prefix-arg)
+                              'toggle)))
 	 (let ((,last-message (current-message)))
            (,@setter
-            (if (eq arg 'toggle)
-                (not ,getter)
-              ;; A nil argument also means ON now.
-              (> (prefix-numeric-value arg) 0)))
+            (cond ((eq arg 'toggle)
+                   (not ,getter))
+                  ((and (numberp arg)
+                        (> arg 0))
+                   t)
+                  ((eq arg nil)
+                   t)
+                  (t
+                   nil)))
            ,@body
            ;; The on/off hooks are here for backward compatibility only.
            (run-hooks ',hook (if ,getter ',hook-on ',hook-off))
diff --git a/test/lisp/emacs-lisp/easy-mmode-tests.el b/test/lisp/emacs-lisp/easy-mmode-tests.el
index 4d7fe9444fb..4a448200a2b 100644
--- a/test/lisp/emacs-lisp/easy-mmode-tests.el
+++ b/test/lisp/emacs-lisp/easy-mmode-tests.el
@@ -44,6 +44,27 @@
                  '(c-mode (not message-mode mail-mode) text-mode))
                 t))))
 
+(ert-deftest easy-mmode--minor-mode ()
+  (with-temp-buffer
+    (define-minor-mode test-mode "A test.")
+    (should (eq test-mode nil))
+    (test-mode t)
+    (should (eq test-mode nil))
+    (test-mode nil)
+    (should (eq test-mode t))
+    (test-mode -33)
+    (should (eq test-mode nil))
+    (test-mode 33)
+    (should (eq test-mode t))
+    (test-mode 0)
+    (should (eq test-mode nil))
+    (test-mode 'toggle)
+    (should (eq test-mode t))
+    (test-mode 'toggle)
+    (should (eq test-mode nil))
+    (test-mode "what")
+    (should (eq test-mode nil))))
+
 (provide 'easy-mmode-tests)
 
 ;;; easy-mmode-tests.el ends here