Add erc-timestamp property to invisible messages

* lisp/erc/erc-fill.el (erc-fill--wrap-beginning-of-line): Pretend
nicks with an empty string as a `display' prop are `invisible-p' and
break out of hidden "merged" nicks after moving.  (Bug#60936.)
* lisp/erc/erc-match.el (erc-hide-fools): Add comment.
* lisp/erc/erc-stamp.el (erc-add-timestamp): Always add
`erc-timestamp' and `cursor-sensor-functions' properties but respect
tradition and don't actually stamp any invisible messages.

3 files changed, 18 insertions, 6 deletions

diff --git a/lisp/erc/erc-fill.el b/lisp/erc/erc-fill.el
index 7b6495f9f3f..a56134d8188 100644
--- a/lisp/erc/erc-fill.el
+++ b/lisp/erc/erc-fill.el
@@ -221,8 +221,13 @@ messages less than a day apart."
   (let ((inhibit-field-text-motion t))
     (erc-fill--wrap-move #'move-beginning-of-line
                          #'beginning-of-visual-line arg))
-  (when (get-text-property (point) 'erc-prompt)
-    (goto-char erc-input-marker)))
+  (if (get-text-property (point) 'erc-prompt)
+      (goto-char erc-input-marker)
+    ;; Mimic what `move-beginning-of-line' does with invisible text.
+    (when-let ((erc-fill-wrap-merge)
+               (empty (get-text-property (point) 'display))
+               ((string-empty-p empty)))
+      (goto-char (text-property-not-all (point) (pos-eol) 'display empty)))))
 
 (defun erc-fill--wrap-end-of-line (arg)
   "Defer to `move-end-of-line' or `end-of-visual-line'."
@@ -389,6 +394,9 @@ See `erc-fill-wrap-mode' for details."
                    (progn
                      (skip-syntax-forward "^-")
                      (forward-char)
+                     ;; Using the `invisible' property might make more
+                     ;; sense, but that would require coordination
+                     ;; with other modules, like `erc-match'.
                      (cond ((and erc-fill-wrap-merge
                                  (erc-fill--wrap-continued-message-p))
                             (put-text-property (point-min) (point)
diff --git a/lisp/erc/erc-match.el b/lisp/erc/erc-match.el
index 82b821503a8..c08a640260c 100644
--- a/lisp/erc/erc-match.el
+++ b/lisp/erc/erc-match.el
@@ -654,6 +654,8 @@ See `erc-log-match-format'."
 
 (defvar-local erc-match--hide-fools-offset-bounds nil)
 
+;; FIXME this should merge with instead of overwrite existing
+;; `invisible' values.
 (defun erc-hide-fools (match-type _nickuserhost _message)
  "Hide foolish comments.
 This function should be called from `erc-text-matched-hook'."
diff --git a/lisp/erc/erc-stamp.el b/lisp/erc/erc-stamp.el
index 61f289a8753..f90a8fc50b1 100644
--- a/lisp/erc/erc-stamp.el
+++ b/lisp/erc/erc-stamp.el
@@ -198,13 +198,15 @@ may not be unique, `equal'-wise."
 
 This function is meant to be called from `erc-insert-modify-hook'
 or `erc-send-modify-hook'."
-  (unless (get-text-property (point-min) 'invisible)
+  (progn ; remove this `progn' on next major refactor
     (let* ((ct (erc-stamp--current-time))
+           (invisible (get-text-property (point-min) 'invisible))
            (erc-stamp--current-time ct))
-      (funcall erc-insert-timestamp-function
-               (erc-format-timestamp ct erc-timestamp-format))
+      (unless invisible
+        (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)
+      (when (and (not invisible) (fboundp erc-insert-away-timestamp-function)
 		 erc-away-timestamp-format
 		 (erc-away-time)
 		 (not erc-timestamp-format))