Improve new connections in erc-handle-irc-url

* doc/misc/erc.texi: Add new Integrations section to the info manual
under Advanced Usage.
* etc/ERC-NEWS: Add new section mentioning improved UX when clicking
on irc:// links.

* lisp/erc/erc.el (erc-handle-irc-url): Add optional "scheme"
parameter.  Fix `erc-open' invocation so that the server buffer is
named correctly by deferring to a new customizable opener.  Arrange
for JOINing a channel in a manner similar to ERC's autojoin module.
(erc-url-connect-function): Add new option for creating a new ERC
connection based on info parsed from a URL.
(erc--url-default-connect-function): New function to serve as an
interactive-only fallback when a user hasn't specified a URL connect
function.
* lisp/erc/erc-compat.el (erc-compat--29-browse-url--irc): Add new
compatibility function for `browse-url-irc' and include it in
`browse-url-default-handlers' on Emacs versions below 29.

* test/lisp/erc/erc-tests.el (erc-tests--make-server-buf,
erc-tests--make-client-buf): Add helpers for creating dummy ERC
buffers.
(erc-handle-irc-url): Add test.
* test/lisp/erc/erc-scenarios-misc.el (erc-scenarios-handle-irc-url):
Add new test.
* test/lisp/erc/resources/join/legacy/foonet.eld: Relax
timeout.  (Bug#56514.)

3 files changed, 123 insertions, 1 deletions

diff --git a/test/lisp/erc/erc-scenarios-misc.el b/test/lisp/erc/erc-scenarios-misc.el
index ded620ccc1d..8557a779069 100644
--- a/test/lisp/erc/erc-scenarios-misc.el
+++ b/test/lisp/erc/erc-scenarios-misc.el
@@ -177,4 +177,32 @@
         (erc-scenarios-common-say "Hi")
         (funcall expect 10 "Hola")))))
 
+(defvar url-irc-function)
+
+(ert-deftest erc-scenarios-handle-irc-url ()
+  :tags '(:expensive-test)
+  (erc-scenarios-common-with-cleanup
+      ((erc-scenarios-common-dialog "join/legacy")
+       (dumb-server (erc-d-run "localhost" t 'foonet))
+       (port (process-contact dumb-server :service))
+       (expect (erc-d-t-make-expecter))
+       (url-irc-function 'url-irc-erc)
+       (erc-url-connect-function
+        (lambda (scheme &rest r)
+          (ert-info ("Connect to foonet")
+            (should (equal scheme "irc"))
+            (with-current-buffer (apply #'erc `(:full-name "tester" ,@r))
+              (should (string= (buffer-name)
+                               (format "127.0.0.1:%d" port)))
+              (current-buffer))))))
+
+    (with-temp-buffer
+      (insert (format ";; irc://tester:changeme@127.0.0.1:%d/#chan" port))
+      (goto-char 10)
+      (browse-url-at-point))
+
+    (ert-info ("Connected")
+      (with-current-buffer (erc-d-t-wait-for 10 (get-buffer "#chan"))
+        (funcall expect 10 "welcome")))))
+
 ;;; erc-scenarios-misc.el ends here
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index db54cb4889f..a5100ec1556 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -1084,4 +1084,98 @@
                        '(nil 7000 nil "Bob's Name" t
                              "bob:changeme" nil nil nil nil "bobo" nil)))))))
 
+(defun erc-tests--make-server-buf (name)
+  (with-current-buffer (get-buffer-create name)
+    (erc-mode)
+    (setq erc-server-process (start-process "sleep" (current-buffer)
+                                            "sleep" "1")
+          erc-session-server (concat "irc." name ".org")
+          erc-session-port 6667
+          erc-network (intern name))
+    (set-process-query-on-exit-flag erc-server-process nil)
+    (current-buffer)))
+
+(defun erc-tests--make-client-buf (server name)
+  (unless (bufferp server)
+    (setq server (get-buffer server)))
+  (with-current-buffer (get-buffer-create name)
+    (erc-mode)
+    (setq erc--target (erc--target-from-string name))
+    (dolist (v '(erc-server-process
+                 erc-session-server
+                 erc-session-port
+                 erc-network))
+      (set v (buffer-local-value v server)))
+    (current-buffer)))
+
+(ert-deftest erc-handle-irc-url ()
+  (let* (calls
+         rvbuf
+         erc-networks-alist
+         erc-kill-channel-hook erc-kill-server-hook erc-kill-buffer-hook
+         (erc-url-connect-function
+          (lambda (&rest r)
+            (push r calls)
+            (if (functionp rvbuf) (funcall rvbuf) rvbuf))))
+
+    (cl-letf (((symbol-function 'erc-cmd-JOIN)
+               (lambda (&rest r) (push r calls))))
+
+      (with-current-buffer (erc-tests--make-server-buf "foonet")
+        (setq rvbuf (current-buffer)))
+      (erc-tests--make-server-buf "barnet")
+      (erc-tests--make-server-buf "baznet")
+
+      (ert-info ("Unknown network")
+        (erc-handle-irc-url "irc.foonet.org" 6667 "#chan" nil nil "irc")
+        (should (equal '("#chan" nil) (pop calls)))
+        (should-not calls))
+
+      (ert-info ("Unknown network, no port")
+        (erc-handle-irc-url "irc.foonet.org" nil "#chan" nil nil "irc")
+        (should (equal '("#chan" nil) (pop calls)))
+        (should-not calls))
+
+      (ert-info ("Known network, no port")
+        (setq erc-networks-alist '((foonet "irc.foonet.org")))
+        (erc-handle-irc-url "irc.foonet.org" nil "#chan" nil nil "irc")
+        (should (equal '("#chan" nil) (pop calls)))
+        (should-not calls))
+
+      (ert-info ("Known network, different port")
+        (erc-handle-irc-url "irc.foonet.org" 6697 "#chan" nil nil "irc")
+        (should (equal '("#chan" nil) (pop calls)))
+        (should-not calls))
+
+      (ert-info ("Known network, existing chan with key")
+        (erc-tests--make-client-buf "foonet" "#chan")
+        (erc-handle-irc-url "irc.foonet.org" nil "#chan?sec" nil nil "irc")
+        (should (equal '("#chan" "sec") (pop calls)))
+        (should-not calls))
+
+      (ert-info ("Unknown network, connect, no chan")
+        (erc-handle-irc-url "irc.gnu.org" nil nil nil nil "irc")
+        (should (equal '("irc" :server "irc.gnu.org") (pop calls)))
+        (should-not calls))
+
+      (ert-info ("Unknown network, connect, chan")
+        (with-current-buffer "foonet"
+          (should-not (local-variable-p 'erc-after-connect)))
+        (setq rvbuf (lambda () (erc-tests--make-server-buf "gnu")))
+        (erc-handle-irc-url "irc.gnu.org" nil "#spam" nil nil "irc")
+        (should (equal '("irc" :server "irc.gnu.org") (pop calls)))
+        (should-not calls)
+        (with-current-buffer "gnu"
+          (should (local-variable-p 'erc-after-connect))
+          (funcall (car erc-after-connect))
+          (should (equal '("#spam" nil) (pop calls)))
+          (should-not (local-variable-p 'erc-after-connect)))
+        (should-not calls))))
+
+  (when noninteractive
+    (kill-buffer "foonet")
+    (kill-buffer "barnet")
+    (kill-buffer "baznet")
+    (kill-buffer "#chan")))
+
 ;;; erc-tests.el ends here
diff --git a/test/lisp/erc/resources/join/legacy/foonet.eld b/test/lisp/erc/resources/join/legacy/foonet.eld
index 344ba7c1daf..4025094a59c 100644
--- a/test/lisp/erc/resources/join/legacy/foonet.eld
+++ b/test/lisp/erc/resources/join/legacy/foonet.eld
@@ -1,5 +1,5 @@
 ;; -*- mode: lisp-data; -*-
-((pass 1 "PASS :changeme"))
+((pass 10 "PASS :changeme"))
 ((nick 1 "NICK tester"))
 ((user 1 "USER user 0 * :tester")
  (0 ":irc.foonet.org 001 tester :Welcome to the foonet IRC Network tester")