Allow ERC's module toggles access to the prefix arg

* lisp/erc/erc-common.el (erc--module-toggle-prefix-arg): Add internal
variable for preserving the `arg' passed to a module's minor-mode
toggle, which was previously discarded.  Doing this lets modules that
are more interactive in nature overload their mode toggles with
alternate behaviors.
(define-erc-module): Bind `erc--module-toggle-prefix-arg' to the `arg'
parameter, which is normally defined inside a `define-minor-mode' body
form.
* test/lisp/erc/erc-tests.el (define-erc-module--global,
define-erc-module--local): Expect activation body to be wrapped by a
let form binding `erc--module-toggle-prefix-arg'.  (Bug#63595)

1 files changed, 11 insertions, 3 deletions

diff --git a/lisp/erc/erc-common.el b/lisp/erc/erc-common.el
index 7bd549abfc1..08c11d518a8 100644
--- a/lisp/erc/erc-common.el
+++ b/lisp/erc/erc-common.el
@@ -289,6 +289,15 @@ instead of a `set' state, which precludes any actual saving."
              (intern (file-name-base file))))
      (v v)))
 
+(defvar erc--module-toggle-prefix-arg nil
+  "The interpreted prefix arg of the minor-mode toggle.
+Non-nil inside an ERC module's activation (or deactivation)
+command, such as `erc-spelling-enable', when it's been called
+indirectly via the module's minor-mode toggle, i.e.,
+`erc-spelling-mode'.  Nil otherwise.  Its value is either the
+symbol `toggle' or an integer produced by `prefix-numeric-value'.
+See Info node `(elisp) Defining Minor Modes' for more.")
+
 (defmacro define-erc-module (name alias doc enable-body disable-body
                                   &optional local-p)
   "Define a new minor mode using ERC conventions.
@@ -337,9 +346,8 @@ if ARG is omitted or nil.
          :group (erc--find-group ',name ,(and alias (list 'quote alias)))
          ,@(unless local-p `(:require ',(erc--find-feature name alias)))
          ,@(unless local-p `(:type ,(erc--prepare-custom-module-type name)))
-         (if ,mode
-             (,enable)
-           (,disable)))
+         (let ((erc--module-toggle-prefix-arg arg))
+           (if ,mode (,enable) (,disable))))
        ,(erc--assemble-toggle local-p name enable mode t enable-body)
        ,(erc--assemble-toggle local-p name disable mode nil disable-body)
        ,@(and-let* ((alias)