>From 454023b0aaf43a68adc2709e57b1d647d5a96374 Mon Sep 17 00:00:00 2001
From: "F. Jason Park" <jp@neverwas.me>
Date: Wed, 24 Nov 2021 05:35:35 -0800
Subject: [PATCH 4/8] [5.6] Make some erc-stamp functions more limber

TODO: update ERC-NEWS announcing deprecation.

* lisp/erc/erc-stamp.el (erc-timestamp-format-right): Deprecate option
and change meaning of its nil value to fall through to
`erc-timestamp-format'.  Do this to allow modules to predict what the
right-hand stamp's final width will be.  This also saves
`erc-insert-timestamp-left-and-right' from calling
`erc-format-timestamp' again for no reason.
(erc-stamp--current-time): Add new generic function and method to
return current time.  Default to calling `current-time'.
(erc-stamp--current-time): New internal variable to hold time value
used to construct time formatted stamp passed to
`erc-insert-timestamp-function'.
(erc-add-timestamp): Bind `erc-stamp--current-time' when calling
`erc-insert-timestamp-function'.
(erc-insert-timestamp-left-and-right): Use STRING parameter and favor
it over the now deprecated `erc-timestamp-format-right' to avoid
formatting twice.  Also extract current time from the variable
`erc-stamp--current-time' for similar reasons.  (Bug#60936.)
---
 lisp/erc/erc-stamp.el | 36 +++++++++++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/lisp/erc/erc-stamp.el b/lisp/erc/erc-stamp.el
index 08cdc1c8518..b9ad61aaf3e 100644
--- a/lisp/erc/erc-stamp.el
+++ b/lisp/erc/erc-stamp.el
@@ -55,6 +55,9 @@ erc-timestamp-format
   :type '(choice (const nil)
 		 (string)))
 
+;; FIXME remove surrounding whitespace from default value and have
+;; `erc-insert-timestamp-left-and-right' add it before insertion.
+
 (defcustom erc-timestamp-format-left "\n[%a %b %e %Y]\n"
   "If set to a string, messages will be timestamped.
 This string is processed using `format-time-string'.
@@ -68,7 +71,7 @@ erc-timestamp-format-left
   :type '(choice (const nil)
 		 (string)))
 
-(defcustom erc-timestamp-format-right " [%H:%M]"
+(defcustom erc-timestamp-format-right nil
   "If set to a string, messages will be timestamped.
 This string is processed using `format-time-string'.
 Good examples are \"%T\" and \"%H:%M\".
@@ -77,9 +80,14 @@ erc-timestamp-format-right
 screen when `erc-insert-timestamp-function' is set to
 `erc-insert-timestamp-left-and-right'.
 
-If nil, timestamping is turned off."
+Unlike `erc-timestamp-format' and `erc-timestamp-format-left', if
+the value of this option is nil, it falls back to using the value
+of `erc-timestamp-format'."
+  :package-version '(ERC . "5.6") ; FIXME sync on release
   :type '(choice (const nil)
 		 (string)))
+(make-obsolete-variable 'erc-timestamp-format-right
+                        'erc-timestamp-format "30.1")
 
 (defcustom erc-insert-timestamp-function 'erc-insert-timestamp-left-and-right
   "Function to use to insert timestamps.
@@ -157,17 +165,31 @@ stamp
    (remove-hook 'erc-insert-modify-hook #'erc-add-timestamp)
    (remove-hook 'erc-send-modify-hook #'erc-add-timestamp)))
 
+(defvar erc-stamp--current-time nil
+  "The current time when calling `erc-insert-timestamp-function'.
+Specifically, this is the same lisp time object used to create
+the stamp passed to `erc-insert-timestamp-function'.")
+
+(cl-defgeneric erc-stamp--current-time ()
+  "Return a lisp time object to associate with an IRC message.
+This becomes the message's `erc-timestamp' text property, which
+may not be unique."
+  (current-time))
+
+(cl-defmethod erc-stamp--current-time :around ()
+  (or erc-stamp--current-time (cl-call-next-method)))
+
 (defun erc-add-timestamp ()
   "Add timestamp and text-properties to message.
 
 This function is meant to be called from `erc-insert-modify-hook'
 or `erc-send-modify-hook'."
   (unless (get-text-property (point-min) 'invisible)
-    (let ((ct (current-time)))
-      (if (fboundp erc-insert-timestamp-function)
-	  (funcall erc-insert-timestamp-function
-		   (erc-format-timestamp ct erc-timestamp-format))
-	(error "Timestamp function unbound"))
+    (let* ((ct (erc-stamp--current-time))
+           (erc-stamp--current-time ct))
+      (funcall erc-insert-timestamp-function
+               (erc-format-timestamp ct erc-timestamp-format))
+      ;; FIXME this will error when advice has been applied.
       (when (and (fboundp erc-insert-away-timestamp-function)
 		 erc-away-timestamp-format
 		 (erc-away-time)
-- 
2.39.1