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.)

1 files changed, 30 insertions, 2 deletions

diff --git a/lisp/erc/erc-compat.el b/lisp/erc/erc-compat.el
index 5b54a0587a1..d23703394be 100644
--- a/lisp/erc/erc-compat.el
+++ b/lisp/erc/erc-compat.el
@@ -32,8 +32,7 @@
 ;;; Code:
 
 (require 'compat nil 'noerror)
-(eval-when-compile (require 'cl-lib))
-
+(eval-when-compile (require 'cl-lib) (require 'url-parse))
 
 ;;;###autoload(autoload 'erc-define-minor-mode "erc-compat")
 (define-obsolete-function-alias 'erc-define-minor-mode
@@ -285,6 +284,35 @@ If START or END is negative, it counts from the end."
     `(cl--generic-with-memoization ,table ,@forms))
    (t `(progn ,@forms))))
 
+(defvar url-irc-function)
+
+(defun erc-compat--29-browse-url-irc (string &rest _)
+  (require 'url-irc)
+  (let* ((url (url-generic-parse-url string))
+         (url-irc-function
+          (if (function-equal url-irc-function 'url-irc-erc)
+              (lambda (host port chan user pass)
+                (erc-handle-irc-url host port chan user pass (url-type url)))
+            url-irc-function)))
+    (url-irc url)))
+
+(cond ((fboundp 'browse-url-irc)) ; 29
+      ((boundp 'browse-url-default-handlers) ; 28
+       (cl-pushnew '("\\`irc6?s?://" . erc-compat--29-browse-url-irc)
+                   browse-url-default-handlers))
+      ((boundp 'browse-url-browser-function) ; 27
+       (require 'browse-url)
+       (let ((existing browse-url-browser-function))
+         (setq browse-url-browser-function
+               (if (functionp existing)
+                   (lambda (u &rest r)
+                     (apply (if (string-match-p "\\`irc6?s?://" u)
+                                #'erc-compat--29-browse-url-irc
+                              existing)
+                            u r))
+                 (cons '("\\`irc6?s?://" . erc-compat--29-browse-url-irc)
+                       existing))))))
+
 (provide 'erc-compat)
 
 ;;; erc-compat.el ends here