Warn of absent networks module in ERC

* doc/misc/erc.texi: Add linkable note in Modules chapter about some
modules being required.  Also tweak markup in auth-source section.
* etc/ERC-NEWS: Mention the special role of `networks'.
* lisp/erc/erc-backend.el (erc--server-post-connect-hook): Add
internal hook for core modules to perform post-network-process,
pre-protocol config validation even when they haven't been loaded.
(erc--register-connection): Run `erc--server-post-connect-hook'.
* lisp/erc/erc-networks.el (erc-networks--bouncer-targets,
erc-networks-on-MOTD-end): Fix comments and doc strings.  Also change
former from constant to internal variable in case adjustment needed
between releases.
(erc-networks--warn-on-connect): New function to warn about the
`networks' module being absent from `erc-modules'.  This could
probably run at any time up to and including when the logical IRC
connection is established, but doing so at the process/protocol
boundary seems ideal.
* lisp/erc/erc-sasl.el (erc--register-connection): Defer to base
method instead of calling `erc-login' explicitly.
* lisp/erc/erc.el (erc-generate-new-buffer-name): Don't reconcile
buffer names when networks module not in play.
(erc-format-target-and/or-network): Don't assume networks module
loaded.
* test/lisp/erc/erc-scenarios-base-unstable.el:
(erc-scenarios-networks-no-module): New test.
* test/lisp/erc/resources/networks/no-module/basic.eld: New test data
file.  (Bug#60331.)

4 files changed, 35 insertions, 9 deletions

diff --git a/lisp/erc/erc-backend.el b/lisp/erc/erc-backend.el
index 43c5faad638..6820bf0d1a3 100644
--- a/lisp/erc/erc-backend.el
+++ b/lisp/erc/erc-backend.el
@@ -320,6 +320,15 @@ session when reconnecting.  Once `erc-reuse-buffers' is retired
 and fully removed, modules can switch to leveraging the
 `permanent-local' property instead.")
 
+(defvar erc--server-post-connect-hook '(erc-networks--warn-on-connect)
+  "Functions to run when a network connection is successfully opened.
+Though internal, this complements `erc-connect-pre-hook' in that
+it bookends the process rather than the logical connection, which
+is the domain of `erc-before-connect' and `erc-after-connect'.
+Note that unlike `erc-connect-pre-hook', this only runs in server
+buffers, and it does so immediately before the first protocol
+exchange.")
+
 (defvar-local erc-server-timed-out nil
   "Non-nil if the IRC server failed to respond to a ping.")
 
@@ -646,6 +655,7 @@ The current buffer is given by BUFFER."
 
 (cl-defmethod erc--register-connection ()
   "Perform opening IRC protocol exchange with server."
+  (run-hooks 'erc--server-post-connect-hook)
   (erc-login))
 
 (defvar erc--server-connect-dumb-ipv6-regexp
diff --git a/lisp/erc/erc-networks.el b/lisp/erc/erc-networks.el
index 2e2d0930118..f05a98be16d 100644
--- a/lisp/erc/erc-networks.el
+++ b/lisp/erc/erc-networks.el
@@ -1472,14 +1472,16 @@ to be a false alarm.  If `erc-reuse-buffers' is nil, let
           (t (rename-buffer (generate-new-buffer-name name)))))
   nil)
 
-;; Soju v0.4.0 only sends ISUPPORT on upstream reconnect, so this
-;; doesn't apply.  ZNC 1.8.2, however, still sends the entire burst.
-(defconst erc-networks--bouncer-targets '(*status bouncerserv)
-  "Case-mapped symbols matching known bouncer service-bot targets.")
+;; Soju v0.4.0 sends ISUPPORT and nothing else on upstream reconnect,
+;; so this actually doesn't apply.  ZNC 1.8.2, however, still sends
+;; the entire burst.
+(defvar erc-networks--bouncer-targets '(*status bouncerserv)
+  "Symbols matching proxy-bot targets.")
 
 (defun erc-networks-on-MOTD-end (proc parsed)
-  "Call on-connect functions with server PROC and PARSED message.
-This must run before `erc-server-connected' is set."
+  "Call on-connect functions with server PROC and PARSED message."
+  ;; This should normally run before `erc-server-connected' is set.
+  ;; However, bouncers and other proxies may interfere with that.
   (when erc-server-connected
     (unless (erc-buffer-filter (lambda ()
                                  (and erc--target
@@ -1502,6 +1504,18 @@ This must run before `erc-server-connected' is set."
   ((remove-hook 'erc-server-376-functions #'erc-networks-on-MOTD-end)
    (remove-hook 'erc-server-422-functions #'erc-networks-on-MOTD-end)))
 
+(defun erc-networks--warn-on-connect ()
+  "Emit warning when the `networks' module hasn't been loaded.
+Ideally, do so upon opening the network process."
+  (unless (or erc--target erc-networks-mode)
+    (require 'info nil t)
+    (let ((m (concat "Required module `networks' not loaded.  If this "
+                     " was unexpected, please add it to `erc-modules'.")))
+      ;; Assume the server buffer has been marked as active.
+      (erc-display-error-notice
+       nil (concat m "  See Info:\"(erc) Required Modules\" for more."))
+      (lwarn 'erc :warning m))))
+
 (defun erc-ports-list (ports)
   "Return a list of PORTS.
 
diff --git a/lisp/erc/erc-sasl.el b/lisp/erc/erc-sasl.el
index 78d02a46381..23110d74b5e 100644
--- a/lisp/erc/erc-sasl.el
+++ b/lisp/erc/erc-sasl.el
@@ -435,7 +435,7 @@ Otherwise, expect it to disappear in subsequent versions.")
                (if (eq :user (alist-get 'user erc-sasl--options))
                    (erc-current-nick)
                  erc-session-username)))
-          (erc-login))
+          (cl-call-next-method))
         (when erc-sasl--send-cap-ls
           (erc-server-send "CAP REQ :sasl"))
         (erc-server-send (format "AUTHENTICATE %s" m)))
diff --git a/lisp/erc/erc.el b/lisp/erc/erc.el
index 6a5e0018964..16a0aba77b1 100644
--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -1607,7 +1607,8 @@ same manner."
   (when target ; compat
     (setq tgt-info (erc--target-from-string target)))
   (if tgt-info
-      (let* ((esid (erc-networks--id-symbol erc-networks--id))
+      (let* ((esid (and erc-networks--id
+                        (erc-networks--id-symbol erc-networks--id)))
              (name (if esid
                        (erc-networks--reconcile-buffer-names tgt-info
                                                              erc-networks--id)
@@ -6760,7 +6761,8 @@ This should be a string with substitution variables recognized by
 If the name of the network is not available, then use the
 shortened server name instead."
   (if-let ((erc--target)
-           (name (if-let ((esid (erc-networks--id-symbol erc-networks--id)))
+           (name (if-let ((erc-networks--id)
+                          (esid (erc-networks--id-symbol erc-networks--id)))
                      (symbol-name esid)
                    (erc-shorten-server-name (or erc-server-announced-name
                                                 erc-session-server)))))