Make some module toggles more resilient in ERC

* lisp/erc/erc-goodies.el (erc-scrolltobottom-mode,
erc-scrolltobottom-enable, erc-move-to-prompt-mode,
erc-move-to-prompt-enable): Guard setup procedure behind
`erc--updating-modules-p'.
* lisp/erc/erc-imenu.el (erc-imenu-mode, erc-imenu-enable,
erc-imenu-disable): Don't run setup when `erc--updating-modules-p' is
non-nil.  Also, don't restrict teardown to buffers of the same
process.
* lisp/erc/erc-match.el (erc-match-mode, erc-match-enable): Run
major-mode hook member immediately outside of `erc-update-modules' in
`erc-open'.
* lisp/erc/erc-spelling.el (erc-spelling-mode, erc-spelling-enable):
Only conditionally run setup immediately.
* lisp/erc/erc-stamp.el (erc-stamp-mode, erc-stamp-enable,
erc-stamp-disable): Run setup hook immediately.  Don't forget to
kill local vars in all ERC buffers during teardown.
* lisp/erc/erc.el (erc--updating-modules-p): New variable that global
modules can use to provide their `erc-mode-hook'-deferred code on
demand while shielding it from running during early ERC buffer
initialization.
(erc-open): Make `erc--updating-modules-p' non-nil while activating
global modules.  (Bug#60936)

lisp/erc/erc-goodies.el

@@ -53,9 +53,8 @@ argument to `recenter'."
   "This mode causes the prompt to stay at the end of the window."
   ((add-hook 'erc-mode-hook #'erc-add-scroll-to-bottom)
    (add-hook 'erc-insert-done-hook #'erc-possibly-scroll-to-bottom)
-   (dolist (buffer (erc-buffer-list))
-     (with-current-buffer buffer
-       (erc-add-scroll-to-bottom))))
+   (unless erc--updating-modules-p
+     (erc-buffer-filter #'erc-add-scroll-to-bottom)))
   ((remove-hook 'erc-mode-hook #'erc-add-scroll-to-bottom)
    (remove-hook 'erc-insert-done-hook #'erc-possibly-scroll-to-bottom)
    (dolist (buffer (erc-buffer-list))
@@ -120,9 +119,8 @@ Put this function on `erc-insert-post-hook' and/or `erc-send-post-hook'."
 (define-erc-module move-to-prompt nil
   "This mode causes the point to be moved to the prompt when typing text."
   ((add-hook 'erc-mode-hook #'erc-move-to-prompt-setup)
-   (dolist (buffer (erc-buffer-list))
-     (with-current-buffer buffer
-       (erc-move-to-prompt-setup))))
+   (unless erc--updating-modules-p
+     (erc-buffer-filter #'erc-move-to-prompt-setup)))
   ((remove-hook 'erc-mode-hook #'erc-move-to-prompt-setup)
    (dolist (buffer (erc-buffer-list))
      (with-current-buffer buffer

lisp/erc/erc-imenu.el

@@ -138,9 +138,10 @@ Don't rely on this function, read it first!"
 ;;;###autoload(autoload 'erc-imenu-mode "erc-imenu" nil t)
 (define-erc-module imenu nil
   "Simple Imenu integration for ERC."
-  ((add-hook 'erc-mode-hook #'erc-imenu-setup))
+  ((add-hook 'erc-mode-hook #'erc-imenu-setup)
+   (unless erc--updating-modules-p (erc-buffer-filter #'erc-imenu-setup)))
   ((remove-hook 'erc-mode-hook #'erc-imenu-setup)
-   (erc-with-all-buffers-of-server erc-server-process nil
+   (erc-with-all-buffers-of-server nil nil
      (when erc-imenu--create-index-function
        (setq imenu-create-index-function erc-imenu--create-index-function)
        (kill-local-variable 'erc-imenu--create-index-function)))))

lisp/erc/erc-match.el

@@ -54,6 +54,8 @@ you can decide whether the entire message or only the sending nick is
 highlighted."
   ((add-hook 'erc-insert-modify-hook #'erc-match-message 'append)
    (add-hook 'erc-mode-hook #'erc-match--modify-invisibility-spec)
+   (unless erc--updating-modules-p
+     (erc-buffer-filter #'erc-match--modify-invisibility-spec))
    (erc--modify-local-map t "C-c C-k" #'erc-go-to-log-matches-buffer))
   ((remove-hook 'erc-insert-modify-hook #'erc-match-message)
    (remove-hook 'erc-mode-hook #'erc-match--modify-invisibility-spec)

lisp/erc/erc-spelling.el

@@ -39,8 +39,9 @@
   ;; Use erc-connect-pre-hook instead of erc-mode-hook as pre-hook is
   ;; called AFTER the server buffer is initialized.
   ((add-hook 'erc-connect-pre-hook #'erc-spelling-init)
-   (dolist (buffer (erc-buffer-list))
-     (erc-spelling-init buffer)))
+   (unless erc--updating-modules-p
+     (erc-with-all-buffers-of-server nil nil
+       (erc-spelling-init (current-buffer)))))
   ((remove-hook 'erc-connect-pre-hook #'erc-spelling-init)
    (dolist (buffer (erc-buffer-list))
      (with-current-buffer buffer (flyspell-mode 0)))))

lisp/erc/erc-stamp.el

@@ -165,11 +165,17 @@ from entering them and instead jump over them."
   ((add-hook 'erc-mode-hook #'erc-munge-invisibility-spec)
    (add-hook 'erc-insert-modify-hook #'erc-add-timestamp t)
    (add-hook 'erc-send-modify-hook #'erc-add-timestamp t)
-   (add-hook 'erc-mode-hook #'erc-stamp--recover-on-reconnect))
+   (add-hook 'erc-mode-hook #'erc-stamp--recover-on-reconnect)
+   (unless erc--updating-modules-p
+     (erc-buffer-filter #'erc-munge-invisibility-spec)))
   ((remove-hook 'erc-mode-hook #'erc-munge-invisibility-spec)
    (remove-hook 'erc-insert-modify-hook #'erc-add-timestamp)
    (remove-hook 'erc-send-modify-hook #'erc-add-timestamp)
-   (remove-hook 'erc-mode-hook #'erc-stamp--recover-on-reconnect)))
+   (remove-hook 'erc-mode-hook #'erc-stamp--recover-on-reconnect)
+   (erc-with-all-buffers-of-server nil nil
+     (kill-local-variable 'erc-timestamp-last-inserted)
+     (kill-local-variable 'erc-timestamp-last-inserted-left)
+     (kill-local-variable 'erc-timestamp-last-inserted-right))))
 
 (defun erc-stamp--recover-on-reconnect ()
   (when-let ((priors (or erc--server-reconnecting erc--target-priors)))

lisp/erc/erc.el

@@ -2084,6 +2084,26 @@ Except ignore all local modules, which were introduced in ERC 5.5."
             (push mode local-modes))
         (error "`%s' is not a known ERC module" module)))))
 
+(defvar erc--updating-modules-p nil
+  "Non-nil when running `erc--update-modules' in `erc-open'.
+This allows global modules with known or likely dependents (or
+some other reason for activating after session initialization) to
+conditionally run setup code traditionally reserved for
+`erc-mode-hook' in the setup portion of their mode toggle.  Note
+that being \"global\", they'll likely want to do so in all ERC
+buffers and ensure the code is idempotent.  For example:
+
+  (add-hook \\='erc-mode-hook #\\='erc-foo-setup-fn)
+  (unless erc--updating-modules-p
+    (erc-with-all-buffers-of-server nil
+        (lambda () some-condition-p)
+      (erc-foo-setup-fn)))
+
+This means that when a dependent module is initializing and
+realizes it's missing some required module \"foo\", it can
+confidently call (erc-foo-mode 1) without having to learn
+anything about the dependency's implementation.")
+
 (defun erc--setup-buffer-first-window (frame a b)
   (catch 'found
     (walk-window-tree
@@ -2243,7 +2263,8 @@ Returns the buffer for the given server or channel."
     (set-buffer buffer)
     (setq old-point (point))
     (setq delayed-modules
-          (erc--merge-local-modes (erc--update-modules)
+          (erc--merge-local-modes (let ((erc--updating-modules-p t))
+                                    (erc--update-modules))
                                   (or erc--server-reconnecting
                                       erc--target-priors)))