bug#60933: 30.0.50; ERC >5.5: Make buttonizing more extensible

["J.P." <jp@neverwas.me>]

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This feature added an internal interface that allows for creating
ephemeral "phantom" users, which help make nickname buttonizing possible
with protocol bridges and chat-history playback. Unfortunately, the
original design cut a major corner that it shouldn't have. Essentially,
I wanted to avoid adding an `erc-channel-user' to accompany every
phantom `erc-server-user' being spoofed, primarily because it's a waste
of space. However, I've come to believe this shortcut won't be worth the
added maintenance burden of having to check for missing objects when
performing related operations. Attached is a patch to fix this.


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From 784cdaeee6d9b5ca7138b0cde0e251b475414201 Mon Sep 17 00:00:00 2001
From: "F. Jason Park" <jp@neverwas.me>
Date: Wed, 6 Sep 2023 19:40:11 -0700
Subject: [PATCH] [5.6] Spoof channel users in erc-button--phantom-users-mode

* lisp/erc/erc-backend.el (erc--cmem-from-nick-function): Update
forward declaration.
(erc-server-PRIVMSG): Use new name for `erc--user-from-nick-function',
now `erc--cmem-from-nick-function'.
* lisp/erc/erc-button.el (erc-button--phantom-users,
erc-button--phantom-cmems): Rename former to latter.
(erc-button--fallback-user-function,
erc-button--fallback-cmem-function): Rename former to latter.
(erc--phantom-channel-user, erc--phantom-server-user): New superficial
`cl-struct' objects subclassing `erc-channel-user' and
`erc-server-user', respectively.
(erc-button--add-phantom-speaker): Look for channel member instead of
server user, creating one if necessary.  Return a made-up
`erc-channel-user' along with the made-up `erc-server-user'.
(erc-button--get-phantom-user, erc-button--get-phantom-cmem): Rename
former to latter.
(erc-button--phantom-users-mode, erc-button--phantom-users-enable,
erc-button--phantom-users-disable): Use updated names for
function-valued interface vars and their implementing functions.
Remove obsolete comment.
(erc-button-add-nickname-buttons): Attempt to query fallback
function, if non-nil, while populating channel member instead of
server user.
* lisp/erc/erc.el (erc--user-from-nick-function,
erc--cmem-from-nick-function): Rename former to latter.
(erc--examine-nick, erc--get-existing-channel-member): Rename former
to latter.  (Bug#60933)
---
 lisp/erc/erc-backend.el |  4 +--
 lisp/erc/erc-button.el  | 66 +++++++++++++++++++++++------------------
 lisp/erc/erc.el         | 13 ++++----
 3 files changed, 46 insertions(+), 37 deletions(-)

diff --git a/lisp/erc/erc-backend.el b/lisp/erc/erc-backend.el
index 9e121ec1e92..fb10ee31c78 100644
--- a/lisp/erc/erc-backend.el
+++ b/lisp/erc/erc-backend.el
@@ -104,7 +104,7 @@
 (defvar erc--called-as-input-p)
 (defvar erc--display-context)
 (defvar erc--target)
-(defvar erc--user-from-nick-function)
+(defvar erc--cmem-from-nick-function)
 (defvar erc-channel-list)
 (defvar erc-channel-users)
 (defvar erc-default-nicks)
@@ -1944,7 +1944,7 @@ erc--server-determine-join-display-context
             ;; at this point.
             (erc-update-channel-member (if privp nick tgt) nick nick
                                        privp nil nil nil nil nil host login nil nil t)
-            (let ((cdata (funcall erc--user-from-nick-function
+            (let ((cdata (funcall erc--cmem-from-nick-function
                                   (erc-downcase nick) sndr parsed)))
               (setq fnick (funcall erc-format-nick-function
                                    (car cdata) (cdr cdata))))))
diff --git a/lisp/erc/erc-button.el b/lisp/erc/erc-button.el
index 8c1188e64a2..620ee63fa39 100644
--- a/lisp/erc/erc-button.el
+++ b/lisp/erc/erc-button.el
@@ -380,32 +380,39 @@ erc-button--modify-nick-function
 all faces defined in `erc-button' are bound temporarily and can
 be updated at will.")
 
-(defvar-local erc-button--phantom-users nil)
+(defvar-local erc-button--phantom-cmems nil)
 
-(defvar erc-button--fallback-user-function #'ignore
-  "Function to determine `erc-server-user' if not found in the usual places.
+(defvar erc-button--fallback-cmem-function #'ignore
+  "Function to determine channel member if not found in the usual places.
 Called with DOWNCASED-NICK, NICK, and NICK-BOUNDS when
 `erc-button-add-nickname-buttons' cannot find a user object for
 DOWNCASED-NICK in `erc-channel-users' or `erc-server-users'.")
 
+;; Historical or fictitious users.  As long as these two structs
+;; remain superficial subclasses with the exact same slots and
+;; defaults, they can live here instead of in erc-common.el.  Modules
+;; can use the named getters for the superclasses when doing `setf'
+;; modifications without having to `require' this library.
+(cl-defstruct (erc--phantom-channel-user (:include erc-channel-user)))
+(cl-defstruct (erc--phantom-server-user (:include erc-server-user)))
+
 (defun erc-button--add-phantom-speaker (downcased nuh _parsed)
-  "Stash fictitious `erc-server-user' while processing \"PRIVMSG\".
-Expect DOWNCASED to be the downcased nickname, NUH to be a triple
-of (NICK LOGIN HOST), and parsed to be an `erc-response' object."
   (pcase-let* ((`(,nick ,login ,host) nuh)
-               (user (or (gethash downcased erc-button--phantom-users)
-                         (make-erc-server-user
+               (cmem (gethash downcased erc-button--phantom-cmems))
+               (user (or (car cmem)
+                         (make-erc--phantom-server-user
                           :nickname nick
                           :host (and (not (string-empty-p host)) host)
-                          :login (and (not (string-empty-p login)) login)))))
-    (list (puthash downcased user erc-button--phantom-users))))
+                          :login (and (not (string-empty-p login)) login))))
+               (cuser (or (cdr cmem)
+                          (make-erc--phantom-channel-user
+                           :last-message-time (current-time)))))
+    (puthash downcased (cons user cuser) erc-button--phantom-cmems)
+    (cons user cuser)))
 
-(defun erc-button--get-phantom-user (down _word _bounds)
-  (gethash down erc-button--phantom-users))
+(defun erc-button--get-phantom-cmem (down _word _bounds)
+  (gethash down erc-button--phantom-cmems))
 
-;; In the future, we'll most likely create temporary
-;; `erc-channel-users' tables during BATCH chathistory playback, thus
-;; obviating the need for this mode entirely.
 (define-minor-mode erc-button--phantom-users-mode
   "Minor mode to recognize unknown speakers.
 Expect to be used by module setup code for creating placeholder
@@ -415,22 +422,22 @@ erc-button--phantom-users-mode
 of the channel.  However, don't bother creating an actual
 `erc-channel-user' object because their status prefix is unknown.
 Instead, just spoof an `erc-server-user' and stash it during
-\"PRIVMSG\" handling via `erc--user-from-nick-function' and
+\"PRIVMSG\" handling via `erc--cmem-from-nick-function' and
 retrieve it during buttonizing via
 `erc-button--fallback-user-function'."
   :interactive nil
   (if erc-button--phantom-users-mode
       (progn
-        (add-function :after-until (local 'erc--user-from-nick-function)
-                      #'erc-button--add-phantom-speaker '((depth . -50)))
-        (add-function :after-until (local 'erc-button--fallback-user-function)
-                      #'erc-button--get-phantom-user '((depth . 50)))
-        (setq erc-button--phantom-users (make-hash-table :test #'equal)))
-    (remove-function (local 'erc--user-from-nick-function)
+        (add-function :after-until (local 'erc--cmem-from-nick-function)
+                      #'erc-button--add-phantom-speaker '((depth . 30)))
+        (add-function :after-until (local 'erc-button--fallback-cmem-function)
+                      #'erc-button--get-phantom-cmem '((depth . 50)))
+        (setq erc-button--phantom-cmems (make-hash-table :test #'equal)))
+    (remove-function (local 'erc--cmem-from-nick-function)
                      #'erc-button--add-phantom-speaker)
-    (remove-function (local 'erc-button--fallback-user-function)
-                     #'erc-button--get-phantom-user)
-    (kill-local-variable 'erc-nicks--phantom-users)))
+    (remove-function (local 'erc-button--fallback-cmem-function)
+                     #'erc-button--get-phantom-cmem)
+    (kill-local-variable 'erc-button--phantom-cmems)))
 
 (defun erc-button-add-nickname-buttons (entry)
   "Search through the buffer for nicknames, and add buttons."
@@ -451,11 +458,12 @@ erc-button-add-nickname-buttons
          (down (erc-downcase word)))
       (let* ((erc-button-mouse-face erc-button-mouse-face)
              (erc-button-nickname-face erc-button-nickname-face)
-             (cuser (and erc-channel-users (gethash down erc-channel-users)))
+             (cuser (and erc-channel-users
+                         (or (gethash down erc-channel-users)
+                             (funcall erc-button--fallback-cmem-function
+                                      down word bounds))))
              (user (or (and cuser (car cuser))
-                       (and erc-server-users (gethash down erc-server-users))
-                       (funcall erc-button--fallback-user-function
-                                down word bounds)))
+                       (and erc-server-users (gethash down erc-server-users))))
              (data (list word)))
         (when (or (not (functionp form))
                   (and-let* ((user)
diff --git a/lisp/erc/erc.el b/lisp/erc/erc.el
index 07ba32d1cca..ba0733f0ee5 100644
--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -5262,14 +5262,15 @@ erc--get-speaker-bounds
                  (next-single-property-change (point-min) 'erc-speaker))))
      (cons beg (next-single-property-change beg 'erc-speaker)))))
 
-(defvar erc--user-from-nick-function #'erc--examine-nick
-  "Function to possibly consider unknown user.
+(defvar erc--cmem-from-nick-function #'erc--get-existing-channel-member
+  "Function returning an `erc-channel-members' object from a nick.
 Must return either nil or a cons of an `erc-server-user' and a
-possibly nil `erc-channel-user' for formatting a server user's
-nick.  Called in the appropriate buffer with the downcased nick,
-the parsed NUH, and the original `erc-response' object.")
+`erc-channel-user' object for formatting a user's nick for
+insertion.  Called in the appropriate target buffer with the
+downcased nick, the parsed NUH, and the current `erc-response'
+object.")
 
-(defun erc--examine-nick (downcased _nuh _parsed)
+(defun erc--get-existing-channel-member (downcased _nuh _parsed)
   (and erc-channel-users (gethash downcased erc-channel-users)))
 
 (defun erc-format-privmessage (nick msg privp msgp)
-- 
2.41.0