master 7ffc79690ad 4/8: Restore missing metadata props in erc-display-line

[F. Jason Park]

branch: master
commit 7ffc79690ad63a09bc5baf99cbbe56654302dc72
Author: F. Jason Park <jp@neverwas.me>
Commit: F. Jason Park <jp@neverwas.me>

    Restore missing metadata props in erc-display-line
    
    * etc/ERC-NEWS: Designate `erc-display-message' as the favored means
    of inserting messages.
    * lisp/erc/erc-fill.el (erc-fill-wrap): Skip any `unknown' `erc-msg'.
    * lisp/erc/erc-stamp.el (erc-stamp--current-time): Use an existing
    `erc-ts' text property, when present, for the current message time.
    * lisp/erc/erc.el (erc-display-line-1, erc-insert-line): Update doc
    string and declare the former an obsolete alias for the latter,
    `erc-insert-line'.  Have `erc-log' label say `erc-display-message'
    even though this function is actually `erc-insert-line'.
    (erc-display-line): Convert to a thin wrapper around
    `erc-display-message', and move its existing body to a new internal
    function, `erc--route-insertion'.
    (erc--route-insertion): Adopt former body of `erc-display-line', now a
    convenience wrapper around `erc-display-message'.  Copy
    `erc--msg-props' hash table when inserting a message in multiple
    buffers.  At present, only `erc-server-QUIT' uses this facility, so
    such a move shouldn't impact performance in any measurable way.  Also,
    improve readability with at most one recursive call for the
    fall-through case.
    (erc--compose-text-properties, erc--merge-text-properties-p): Rename
    former to latter to avoid confusion with `composition' property.
    (erc-display-message): Update doc string.  Attempt to adapt a non-nil
    TYPE parameter for use as the value of the `erc-msg' text property
    before resorting to a value of `unknown'.  But only do this when
    PARSED is nil, and MSG is a string.  Call `erc--route-insertion'
    instead of `erc-display-line'.  Use new name for
    `erc--compose-text-properties'.
    (erc-put-text-property): Update name of variable
    `erc--compose-text-properties'.
    * test/lisp/erc/erc-networks-tests.el (erc-networks--set-name): Mock
    `erc--route-insertion' instead of `erc-display-line'.
    * test/lisp/erc/erc-scenarios-display-message.el: New file.
    * test/lisp/erc/erc-tests.el (erc--route-insertion): New test.
    * test/lisp/erc/resources/base/display-message/multibuf.eld: New test
    data.
    ; * test/lisp/erc/resources/fill/snapshots/merge-01-start.eld: Update.
    ; * test/lisp/erc/resources/fill/snapshots/merge-02-right.eld: Update.
    ; * test/lisp/erc/resources/fill/snapshots/merge-wrap-01.eld: Update.
    ; * test/lisp/erc/resources/fill/snapshots/monospace-01-start.eld: Update.
    ; * test/lisp/erc/resources/fill/snapshots/monospace-02-right.eld: Update.
    ; * test/lisp/erc/resources/fill/snapshots/monospace-03-left.eld: Update.
    ; * test/lisp/erc/resources/fill/snapshots/monospace-04-reset.eld: Update.
    ; * test/lisp/erc/resources/fill/snapshots/spacing-01-mono.eld: Update.
    ; * test/lisp/erc/resources/fill/snapshots/stamps-left-01.eld: Update.
    (Bug#60936)
---
 etc/ERC-NEWS                                       |  23 ++++
 lisp/erc/erc-fill.el                               |   3 +-
 lisp/erc/erc-stamp.el                              |   4 +-
 lisp/erc/erc.el                                    | 146 +++++++++++++--------
 test/lisp/erc/erc-networks-tests.el                |   2 +-
 test/lisp/erc/erc-scenarios-display-message.el     |  64 +++++++++
 test/lisp/erc/erc-tests.el                         |  63 +++++++++
 .../resources/base/display-message/multibuf.eld    |  45 +++++++
 .../resources/fill/snapshots/merge-01-start.eld    |   2 +-
 .../resources/fill/snapshots/merge-02-right.eld    |   2 +-
 .../erc/resources/fill/snapshots/merge-wrap-01.eld |   2 +-
 .../fill/snapshots/monospace-01-start.eld          |   2 +-
 .../fill/snapshots/monospace-02-right.eld          |   2 +-
 .../resources/fill/snapshots/monospace-03-left.eld |   2 +-
 .../fill/snapshots/monospace-04-reset.eld          |   2 +-
 .../resources/fill/snapshots/spacing-01-mono.eld   |   2 +-
 .../resources/fill/snapshots/stamps-left-01.eld    |   2 +-
 17 files changed, 301 insertions(+), 67 deletions(-)

diff --git a/etc/ERC-NEWS b/etc/ERC-NEWS
index 2e56539f210..e47c42a51a6 100644
--- a/etc/ERC-NEWS
+++ b/etc/ERC-NEWS
@@ -288,6 +288,29 @@ ERC also provisionally reserves the same depth interval for
 continue to modify non-ERC hooks locally whenever possible, especially
 in new code.
 
+*** A singular entry point for inserting messages.
+Displaying "local" messages, like help text and interactive-command
+feedback, in ERC buffers has never been straightforward.  As such,
+ancient patterns, like the pairing of preformatted "notice" text with
+ERC's oldest insertion function, 'erc-display-line', still appear
+quite frequently in the wild despite having been largely phased out of
+ERC's own code base in 2002.  That this example has endured makes some
+sense because it's probably seen as less cumbersome than fiddling with
+the more powerful and complicated 'erc-display-message'.
+
+The latest twist in this saga comes with this release, in which a
+healthy bit of "pre-insertion" business has taken up residence in
+'erc-display-message'.  While this would seem to put antiquated
+patterns, like the above mentioned 'erc-make-notice' combo, at risk of
+having messages ignored or subject to degraded treatment by built-in
+modules, an adaptive measure has been introduced that recasts
+'erc-display-line' as a thin wrapper around 'erc-display-message'.
+And though nothing of the sort has been done for the lower-level
+'erc-display-line-1' (now an obsolete alias for 'erc-insert-line'),
+some last-ditch fallback code is in place to ensure baseline
+functionality.  As always, if you find these developments disturbing,
+please say so on the tracker.
+
 *** ERC now manages timestamp-related properties a bit differently.
 For starters, the 'cursor-sensor-functions' text property is absent by
 default unless the option 'erc-echo-timestamps' is already enabled on
diff --git a/lisp/erc/erc-fill.el b/lisp/erc/erc-fill.el
index 0048956e075..e28c3563ebf 100644
--- a/lisp/erc/erc-fill.el
+++ b/lisp/erc/erc-fill.el
@@ -539,7 +539,8 @@ See `erc-fill-wrap-mode' for details."
     (goto-char (point-min))
     (let ((len (or (and erc-fill--wrap-length-function
                         (funcall erc-fill--wrap-length-function))
-                   (and-let* ((msg-prop (erc--check-msg-prop 'erc-msg)))
+                   (and-let* ((msg-prop (erc--check-msg-prop 'erc-msg))
+                              ((not (eq msg-prop 'unknown))))
                      (when-let ((e (erc--get-speaker-bounds))
                                 (b (pop e))
                                 ((or erc-fill--wrap-action-dedent-p
diff --git a/lisp/erc/erc-stamp.el b/lisp/erc/erc-stamp.el
index 394643c03cb..57fd7f39e50 100644
--- a/lisp/erc/erc-stamp.el
+++ b/lisp/erc/erc-stamp.el
@@ -219,7 +219,9 @@ This becomes the message's `erc-ts' text property."
   (erc-compat--current-lisp-time))
 
 (cl-defmethod erc-stamp--current-time :around ()
-  (or erc-stamp--current-time (cl-call-next-method)))
+  (or erc-stamp--current-time
+      (and erc--msg-props (gethash 'erc-ts erc--msg-props))
+      (cl-call-next-method)))
 
 (defvar erc-stamp--skip nil
   "Non-nil means inhibit `erc-add-timestamp' completely.")
diff --git a/lisp/erc/erc.el b/lisp/erc/erc.el
index a4c52389367..f2c93d29d5c 100644
--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -3015,13 +3015,26 @@ Expect callers to know that this doesn't wrap BODY in
 (defvar erc--insert-marker nil
   "Internal override for `erc-insert-marker'.")
 
-(defun erc-display-line-1 (string buffer)
-  "Display STRING in `erc-mode' BUFFER.
-Auxiliary function used in `erc-display-line'.  The line gets filtered to
-interpret the control characters.  Then, `erc-insert-pre-hook' gets called.
-If `erc-insert-this' is still t, STRING gets inserted into the buffer.
-Afterwards, `erc-insert-modify' and `erc-insert-post-hook' get called.
-If STRING is nil, the function does nothing."
+(define-obsolete-function-alias 'erc-display-line-1 'erc-insert-line "30.1")
+(defun erc-insert-line (string buffer)
+  "Insert STRING in an `erc-mode' BUFFER.
+When STRING is nil, do nothing.  Otherwise, start off by running
+`erc-insert-pre-hook' in BUFFER with `erc-insert-this' bound to
+t.  If the latter remains non-nil afterward, insert STRING into
+BUFFER, ensuring a trailing newline.  After that, narrow BUFFER
+around STRING, along with its final line ending, and run
+`erc-insert-modify' and `erc-insert-post-hook', respectively.  In
+all cases, run `erc-insert-done-hook' unnarrowed before exiting,
+and update positions in `buffer-undo-list'.
+
+In general, expect to be called from a higher-level insertion
+function, like `erc-display-message', especially when modules
+should consider STRING as a candidate for formatting with
+enhancements like indentation, fontification, timestamping, etc.
+Otherwise, when called directly, allow built-in modules to ignore
+STRING, which may make it appear incongruous in situ (unless
+preformatted or anticipated by third-party members of the various
+modification hooks)."
   (when string
     (with-current-buffer (or buffer (process-buffer erc-server-process))
       (let ((insert-position (marker-position erc-insert-marker)))
@@ -3033,7 +3046,7 @@ If STRING is nil, the function does nothing."
             (when (erc-string-invisible-p string)
               (erc-put-text-properties 0 (length string)
                                        '(invisible intangible) string)))
-          (erc-log (concat "erc-display-line: " string
+          (erc-log (concat "erc-display-message: " string
                            (format "(%S)" string) " in buffer "
                            (format "%s" buffer)))
           (setq erc-insert-this t)
@@ -3103,39 +3116,45 @@ If STRING is nil, the function does nothing."
   "Check if NICK is a valid IRC nickname."
   (string-match (concat "\\`" erc-valid-nick-regexp "\\'") nick))
 
-(defun erc-display-line (string &optional buffer)
-  "Display STRING in the ERC BUFFER.
-All screen output must be done through this function.  If BUFFER is nil
-or omitted, the default ERC buffer for the `erc-session-server' is used.
-The BUFFER can be an actual buffer, a list of buffers, `all' or `active'.
-If BUFFER = `all', the string is displayed in all the ERC buffers for the
-current session.  `active' means the current active buffer
-\(`erc-active-buffer').  If the buffer can't be resolved, the current
-buffer is used.  `erc-display-line-1' is used to display STRING.
-
-If STRING is nil, the function does nothing."
-  (let (new-bufs)
+(defun erc--route-insertion (string buffer)
+  "Insert STRING in BUFFER.
+See `erc-display-message' for acceptable BUFFER types."
+  (let (seen msg-props)
     (dolist (buf (cond
                   ((bufferp buffer) (list buffer))
-                  ((listp buffer) buffer)
+                  ((consp buffer)
+                   (setq msg-props erc--msg-props)
+                   buffer)
                   ((processp buffer) (list (process-buffer buffer)))
                   ((eq 'all buffer)
                    ;; Hmm, or all of the same session server?
                    (erc-buffer-list nil erc-server-process))
-                  ((and (eq 'active buffer) (erc-active-buffer))
-                   (list (erc-active-buffer)))
+                  ((and-let* (((eq 'active buffer))
+                              (b (erc-active-buffer)))
+                        (list b)))
                   ((erc-server-buffer-live-p)
                    (list (process-buffer erc-server-process)))
                   (t (list (current-buffer)))))
       (when (buffer-live-p buf)
-        (erc-display-line-1 string buf)
-        (push buf new-bufs)))
-    (when (null new-bufs)
-      (erc-display-line-1 string (if (erc-server-buffer-live-p)
-                                     (process-buffer erc-server-process)
-                                   (current-buffer))))))
-
-(defvar erc--compose-text-properties nil
+        (when msg-props
+          (setq erc--msg-props (copy-hash-table msg-props)))
+        (erc-insert-line string buf)
+        (setq seen t)))
+    (unless (or seen (null buffer))
+      (erc--route-insertion string nil))))
+
+(defun erc-display-line (string &optional buffer)
+  "Insert STRING in BUFFER as a plain \"local\" message.
+Take pains to ensure modification hooks see messages created by
+the old pattern (erc-display-line (erc-make-notice) my-buffer) as
+being equivalent to a `erc-display-message' TYPE of `notice'."
+  (let ((erc--msg-prop-overrides erc--msg-prop-overrides))
+    (when (eq 'erc-notice-face (get-text-property 0 'font-lock-face string))
+      (unless (assq 'erc-msg erc--msg-prop-overrides)
+        (push '(erc-msg . notice) erc--msg-prop-overrides)))
+    (erc-display-message nil nil buffer string)))
+
+(defvar erc--merge-text-properties-p nil
   "Non-nil when `erc-put-text-property' defers to `erc--merge-prop'.")
 
 ;; To save space, we could maintain a map of all readable property
@@ -3444,14 +3463,24 @@ returns non-nil."
 Insert MSG or text derived from MSG into an ERC buffer, possibly
 after applying formatting by way of either a `format-spec' known
 to a message-catalog entry or a TYPE known to a specialized
-string handler.  Additionally, derive internal metadata, faces,
-and other text properties from the various overloaded parameters,
-such as PARSED, when it's an `erc-response' object, and MSG, when
-it's a key (symbol) for a \"message catalog\" entry.  Expect
-ARGS, when applicable, to be `format-spec' args known to such an
-entry, and TYPE, when non-nil, to be a symbol handled by
+string handler.  Additionally, derive metadata, faces, and other
+text properties from the various overloaded parameters, such as
+PARSED, when it's an `erc-response' object, and MSG, when it's a
+key (symbol) for a \"message catalog\" entry.  Expect ARGS, when
+applicable, to be `format-spec' args known to such an entry, and
+TYPE, when non-nil, to be a symbol handled by
 `erc-display-message-highlight' (necessarily accompanied by a
-string MSG).
+string MSG).  Expect BUFFER to be among the sort accepted by the
+function `erc-display-line'.
+
+Expect BUFFER to be a live `erc-mode' buffer, a list of such
+buffers, or the symbols `all' or `active'.  If `all', insert
+STRING in all buffers for the current session.  If `active',
+defer to the function `erc-active-buffer', which may return the
+session's server buffer if the previously active buffer has been
+killed.  If BUFFER is nil or a network process, pretend it's set
+to the appropriate server buffer.  Otherwise, use the current
+buffer.
 
 When TYPE is a list of symbols, call handlers from left to right
 without influencing how they behave when encountering existing
@@ -3463,24 +3492,31 @@ expect a TYPE of (t notice error) to result in 
`font-lock-face'
 being (erc-error-face erc-notice-face) throughout MSG when
 `erc-notice-highlight-type' is left at its default, `all'.
 
-As of ERC 5.6, assume user code will use this function instead of
-`erc-display-line' when it's important that insert hooks treat
-MSG in a manner befitting messages received from a server.  That
-is, expect to process most nontrivial informational messages, for
-which PARSED is typically nil, when the caller desires
-buttonizing and other effects."
+As of ERC 5.6, assume third-party code will use this function
+instead of lower-level ones, like `erc-insert-line', when needing
+ERC to process arbitrary informative messages as if they'd been
+sent from a server.  That is, guarantee \"local\" messages, for
+which PARSED is typically nil, will be subject to buttonizing,
+filling, and other effects."
   (let ((string (if (symbolp msg)
                     (apply #'erc-format-message msg args)
                   msg))
         (erc--msg-props
          (or erc--msg-props
-             (let* ((table (make-hash-table :size 5))
-                    (cmd (and parsed (erc--get-eq-comparable-cmd
-                                      (erc-response.command parsed))))
-                    (m (cond ((and msg (symbolp msg)) msg)
-                             ((and cmd (memq cmd '(PRIVMSG NOTICE)) 'msg))
-                             (t 'unknown))))
-               (puthash 'erc-msg m table)
+             (let ((table (make-hash-table :size 5))
+                   (cmd (and parsed (erc--get-eq-comparable-cmd
+                                     (erc-response.command parsed)))))
+               (puthash 'erc-msg
+                        (cond ((and msg (symbolp msg)) msg)
+                              ((and cmd (memq cmd '(PRIVMSG NOTICE)) 'msg))
+                              (type (pcase type
+                                      ((pred symbolp) type)
+                                      ((pred listp)
+                                       (intern (mapconcat #'prin1-to-string
+                                                          type "-")))
+                                      (_ 'unknown)))
+                              (t 'unknown))
+                        table)
                (when cmd
                  (puthash 'erc-cmd cmd table))
                (and erc--msg-prop-overrides
@@ -3493,7 +3529,7 @@ buttonizing and other effects."
            ((null type)
             string)
            ((listp type)
-            (let ((erc--compose-text-properties
+            (let ((erc--merge-text-properties-p
                    (and (eq (car type) t) (setq type (cdr type)))))
               (dolist (type type)
                 (setq string (erc-display-message-highlight type string))))
@@ -3502,13 +3538,13 @@ buttonizing and other effects."
             (erc-display-message-highlight type string))))
 
     (if (not (erc-response-p parsed))
-        (erc-display-line string buffer)
+        (erc--route-insertion string buffer)
       (unless (erc-hide-current-message-p parsed)
         (erc-put-text-property 0 (length string) 'erc-parsed parsed string)
        (when (erc-response.tags parsed)
          (erc-put-text-property 0 (length string) 'tags (erc-response.tags 
parsed)
                                 string))
-       (erc-display-line string buffer)))))
+        (erc--route-insertion string buffer)))))
 
 (defun erc-message-type-member (position list)
   "Return non-nil if the erc-parsed text-property at POSITION is in LIST.
@@ -6493,7 +6529,7 @@ OBJECT is modified without being copied first.
 
 You can redefine or `defadvice' this function in order to add
 EmacsSpeak support."
-  (if erc--compose-text-properties
+  (if erc--merge-text-properties-p
       (erc--merge-prop start end property value object)
     (put-text-property start end property value object)))
 
diff --git a/test/lisp/erc/erc-networks-tests.el 
b/test/lisp/erc/erc-networks-tests.el
index e95d99c128f..45ef0d10a6e 100644
--- a/test/lisp/erc/erc-networks-tests.el
+++ b/test/lisp/erc/erc-networks-tests.el
@@ -1206,7 +1206,7 @@
           calls)
       (erc-mode)
 
-      (cl-letf (((symbol-function 'erc-display-line)
+      (cl-letf (((symbol-function 'erc--route-insertion)
                  (lambda (&rest r) (push r calls))))
 
         (ert-info ("Signals when `erc-server-announced-name' unset")
diff --git a/test/lisp/erc/erc-scenarios-display-message.el 
b/test/lisp/erc/erc-scenarios-display-message.el
new file mode 100644
index 00000000000..51bdf305ad5
--- /dev/null
+++ b/test/lisp/erc/erc-scenarios-display-message.el
@@ -0,0 +1,64 @@
+;;; erc-scenarios-display-message.el --- erc-display-message -*- 
lexical-binding: t -*-
+
+;; Copyright (C) 2023 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Code:
+
+(require 'ert-x)
+(eval-and-compile
+  (let ((load-path (cons (ert-resource-directory) load-path)))
+    (require 'erc-scenarios-common)))
+
+(ert-deftest erc-scenarios-display-message--multibuf ()
+  :tags '(:expensive-test)
+  (erc-scenarios-common-with-cleanup
+      ((erc-scenarios-common-dialog "base/display-message")
+       (dumb-server (erc-d-run "localhost" t 'multibuf))
+       (port (process-contact dumb-server :service))
+       (erc-server-flood-penalty 0.1)
+       (erc-modules (cons 'fill-wrap erc-modules))
+       (erc-autojoin-channels-alist '((foonet "#chan")))
+       (expect (erc-d-t-make-expecter)))
+
+    (ert-info ("Connect to foonet")
+      (with-current-buffer (erc :server "127.0.0.1"
+                                :port port
+                                :nick "tester"
+                                :full-name "tester")
+        (funcall expect 10 "debug mode")))
+
+    (ert-info ("User dummy is a member of #chan")
+      (with-current-buffer (erc-d-t-wait-for 5 (get-buffer "#chan"))
+        (funcall expect 10 "dummy")))
+
+    (ert-info ("Dummy's QUIT notice in query contains metadata props")
+      (with-current-buffer (erc-d-t-wait-for 5 (get-buffer "dummy"))
+        (funcall expect 10 "<dummy> hi")
+        (funcall expect 10 "*** dummy (~u@rdjcgiwfuwqmc.irc) has quit")
+        (should (eq 'QUIT (get-text-property (match-beginning 0) 'erc-msg)))))
+
+    (ert-info ("Dummy's QUIT notice in #chan contains metadata props")
+      (with-current-buffer (erc-d-t-wait-for 5 (get-buffer "#chan"))
+        (funcall expect 10 "*** dummy (~u@rdjcgiwfuwqmc.irc) has quit")
+        (should (eq 'QUIT (get-text-property (match-beginning 0) 'erc-msg)))))
+
+    (erc-cmd-QUIT "")))
+
+(eval-when-compile (require 'erc-join))
+
+;;; erc-scenarios-display-message.el ends here
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index 4f4662f5075..02dfc55b6d5 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -1938,6 +1938,69 @@
                2 5 (erc-speaker "Bob" font-lock-face erc-nick-default-face)
                5 12 (font-lock-face erc-default-face))))))
 
+(ert-deftest erc--route-insertion ()
+  (erc-tests--send-prep)
+  (erc-tests--set-fake-server-process "sleep" "1")
+  (setq erc-networks--id (erc-networks--id-create 'foonet))
+
+  (let* ((erc-modules) ; for `erc--open-target'
+         (server-buffer (current-buffer))
+         (spam-buffer (save-excursion (erc--open-target "#spam")))
+         (chan-buffer (save-excursion (erc--open-target "#chan")))
+         calls)
+    (cl-letf (((symbol-function 'erc-insert-line)
+               (lambda (&rest r) (push (cons 'line-1 r) calls))))
+
+      (with-current-buffer chan-buffer
+
+        (ert-info ("Null `buffer' routes to live server-buffer")
+          (erc--route-insertion "null" nil)
+          (should (equal (pop calls) `(line-1 "null" ,server-buffer)))
+          (should-not calls))
+
+        (ert-info ("Cons `buffer' routes to live members")
+          ;; Copies a let-bound `erc--msg-props' before mutating.
+          (let* ((table (map-into '(erc-msg msg) 'hash-table))
+                 (erc--msg-props table))
+            (erc--route-insertion "cons" (list server-buffer spam-buffer))
+            (should-not (eq table erc--msg-props)))
+          (should (equal (pop calls) `(line-1 "cons" ,spam-buffer)))
+          (should (equal (pop calls) `(line-1 "cons" ,server-buffer)))
+          (should-not calls))
+
+        (ert-info ("Variant `all' inserts in all session buffers")
+          (erc--route-insertion "all" 'all)
+          (should (equal (pop calls) `(line-1 "all" ,chan-buffer)))
+          (should (equal (pop calls) `(line-1 "all" ,spam-buffer)))
+          (should (equal (pop calls) `(line-1 "all" ,server-buffer)))
+          (should-not calls))
+
+        (ert-info ("Variant `active' routes to active buffer if alive")
+          (should (eq chan-buffer (erc-with-server-buffer erc-active-buffer)))
+          (erc-set-active-buffer spam-buffer)
+          (erc--route-insertion "act" 'active)
+          (should (equal (pop calls) `(line-1 "act" ,spam-buffer)))
+          (should (eq (erc-active-buffer) spam-buffer))
+          (should-not calls))
+
+        (ert-info ("Variant `active' falls back to current buffer")
+          (should (eq spam-buffer (erc-active-buffer)))
+          (kill-buffer "#spam")
+          (erc--route-insertion "nact" 'active)
+          (should (equal (pop calls) `(line-1 "nact" ,server-buffer)))
+          (should (eq (erc-with-server-buffer erc-active-buffer)
+                      server-buffer))
+          (should-not calls))
+
+        (ert-info ("Dead single buffer defaults to live server-buffer")
+          (should-not (get-buffer "#spam"))
+          (erc--route-insertion "dead" 'spam-buffer)
+          (should (equal (pop calls) `(line-1 "dead" ,server-buffer)))
+          (should-not calls))))
+
+    (should-not (buffer-live-p spam-buffer))
+    (kill-buffer chan-buffer)))
+
 (defvar erc-tests--ipv6-examples
   '("1:2:3:4:5:6:7:8"
     "::ffff:10.0.0.1" "::ffff:1.2.3.4" "::ffff:0.0.0.0"
diff --git a/test/lisp/erc/resources/base/display-message/multibuf.eld 
b/test/lisp/erc/resources/base/display-message/multibuf.eld
new file mode 100644
index 00000000000..e49a654cd06
--- /dev/null
+++ b/test/lisp/erc/resources/base/display-message/multibuf.eld
@@ -0,0 +1,45 @@
+;; -*- mode: lisp-data; -*-
+((nick 10 "NICK tester"))
+((user 10 "USER user 0 * :tester")
+ (0.00 ":irc.foonet.org 001 tester :Welcome to the foonet IRC Network tester")
+ (0.01 ":irc.foonet.org 002 tester :Your host is irc.foonet.org, running 
version ergo-v2.11.1")
+ (0.01 ":irc.foonet.org 003 tester :This server was created Sat, 14 Oct 2023 
16:08:20 UTC")
+ (0.02 ":irc.foonet.org 004 tester irc.foonet.org ergo-v2.11.1 BERTZios 
CEIMRUabefhiklmnoqstuv Iabefhkloqv")
+ (0.00 ":irc.foonet.org 005 tester AWAYLEN=390 BOT=B CASEMAPPING=ascii 
CHANLIMIT=#:100 CHANMODES=Ibe,k,fl,CEMRUimnstu CHANNELLEN=64 CHANTYPES=# 
CHATHISTORY=1000 ELIST=U EXCEPTS EXTBAN=,m FORWARD=f INVEX :are supported by 
this server")
+ (0.01 ":irc.foonet.org 005 tester KICKLEN=390 MAXLIST=beI:60 MAXTARGETS=4 
MODES MONITOR=100 NETWORK=foonet NICKLEN=32 PREFIX=(qaohv)~&@%+ STATUSMSG=~&@%+ 
TARGMAX=NAMES:1,LIST:1,KICK:,WHOIS:1,USERHOST:10,PRIVMSG:4,TAGMSG:4,NOTICE:4,MONITOR:100
 TOPICLEN=390 UTF8ONLY WHOX :are supported by this server")
+ (0.01 ":irc.foonet.org 005 tester draft/CHATHISTORY=1000 :are supported by 
this server")
+ (0.00 ":irc.foonet.org 251 tester :There are 0 users and 5 invisible on 1 
server(s)")
+ (0.00 ":irc.foonet.org 252 tester 0 :IRC Operators online")
+ (0.00 ":irc.foonet.org 253 tester 0 :unregistered connections")
+ (0.00 ":irc.foonet.org 254 tester 2 :channels formed")
+ (0.00 ":irc.foonet.org 255 tester :I have 5 clients and 0 servers")
+ (0.00 ":irc.foonet.org 265 tester 5 5 :Current local users 5, max 5")
+ (0.02 ":irc.foonet.org 266 tester 5 5 :Current global users 5, max 5")
+ (0.01 ":irc.foonet.org 422 tester :MOTD File is missing")
+ (0.00 ":irc.foonet.org 221 tester +i")
+ (0.01 ":irc.foonet.org NOTICE tester :This server is in debug mode and is 
logging all user I/O. If you do not wish for everything you send to be readable 
by the server owner(s), please disconnect."))
+
+((mode 10 "MODE tester +i")
+ (0.00 ":irc.foonet.org 221 tester +i"))
+
+((join 10 "JOIN #chan")
+ (0.03 ":tester!~u@rdjcgiwfuwqmc.irc JOIN #chan")
+ (0.03 ":irc.foonet.org 353 tester = #chan :@fsbot bob alice dummy tester")
+ (0.01 ":irc.foonet.org 366 tester #chan :End of NAMES list")
+ (0.00 ":bob!~u@uee7kge7ua5sy.irc PRIVMSG #chan :tester, welcome!")
+ (0.01 ":alice!~u@uee7kge7ua5sy.irc PRIVMSG #chan :tester, welcome!"))
+
+((mode 10 "MODE #chan")
+ (0.01 ":bob!~u@uee7kge7ua5sy.irc PRIVMSG #chan :alice: Persuade this rude 
wretch willingly to die.")
+ (0.01 ":irc.foonet.org 324 tester #chan +Cnt")
+ (0.01 ":irc.foonet.org 329 tester #chan 1697299707")
+ (0.03 ":alice!~u@uee7kge7ua5sy.irc PRIVMSG #chan :bob: It might be yours or 
hers, for aught I know.")
+ (0.07 ":bob!~u@uee7kge7ua5sy.irc PRIVMSG #chan :Would all themselves laugh 
mortal.")
+ (0.04 ":dummy!~u@rdjcgiwfuwqmc.irc PRIVMSG tester :hi")
+ (0.06 ":bob!~u@uee7kge7ua5sy.irc PRIVMSG #chan :alice: It hath pleased the 
devil drunkenness to give place to the devil wrath; one unperfectness shows me 
another, to make me frankly despise myself.")
+ (0.05 ":dummy!~u@rdjcgiwfuwqmc.irc QUIT :Quit: \2ERC\2 5.6-git (IRC client 
for GNU Emacs 30.0.50)")
+ (0.08 ":alice!~u@uee7kge7ua5sy.irc PRIVMSG #chan :You speak of him when he 
was less furnished than now he is with that which makes him both without and 
within."))
+
+((quit 10 "QUIT :\2ERC\2")
+ (0.04 ":tester!~u@rdjcgiwfuwqmc.irc QUIT :Quit: \2ERC\2 5.x (IRC client for 
GNU Emacs)")
+ (0.02 "ERROR :Quit: \2ERC\2 5.x (IRC client for GNU Emacs)"))
diff --git a/test/lisp/erc/resources/fill/snapshots/merge-01-start.eld 
b/test/lisp/erc/resources/fill/snapshots/merge-01-start.eld
index 238d8cc73c2..8a6f2289f5d 100644
--- a/test/lisp/erc/resources/fill/snapshots/merge-01-start.eld
+++ b/test/lisp/erc/resources/fill/snapshots/merge-01-start.eld
@@ -1 +1 @@
-#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n\n[Sat Apr  1 
2023]\n<bob> zero.[07:00]\n<alic [...]
\ No newline at end of file
+#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n\n[Sat Apr  1 
2023]\n<bob> zero.[07:00]\n<alic [...]
diff --git a/test/lisp/erc/resources/fill/snapshots/merge-02-right.eld 
b/test/lisp/erc/resources/fill/snapshots/merge-02-right.eld
index d1ce9198e69..3eb4be4919b 100644
--- a/test/lisp/erc/resources/fill/snapshots/merge-02-right.eld
+++ b/test/lisp/erc/resources/fill/snapshots/merge-02-right.eld
@@ -1 +1 @@
-#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n\n[Sat Apr  1 
2023]\n<bob> zero.[07:00]\n<alic [...]
\ No newline at end of file
+#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n\n[Sat Apr  1 
2023]\n<bob> zero.[07:00]\n<alic [...]
diff --git a/test/lisp/erc/resources/fill/snapshots/merge-wrap-01.eld 
b/test/lisp/erc/resources/fill/snapshots/merge-wrap-01.eld
index d70184724ba..82c6d52cf7c 100644
--- a/test/lisp/erc/resources/fill/snapshots/merge-wrap-01.eld
+++ b/test/lisp/erc/resources/fill/snapshots/merge-wrap-01.eld
@@ -1 +1 @@
-#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n\n[Sat Apr  1 
2023]\n<bob> zero.[07:00]\n* bob [...]
\ No newline at end of file
+#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n\n[Sat Apr  1 
2023]\n<bob> zero.[07:00]\n* bob [...]
diff --git a/test/lisp/erc/resources/fill/snapshots/monospace-01-start.eld 
b/test/lisp/erc/resources/fill/snapshots/monospace-01-start.eld
index def97738ce6..84a1e34670c 100644
--- a/test/lisp/erc/resources/fill/snapshots/monospace-01-start.eld
+++ b/test/lisp/erc/resources/fill/snapshots/monospace-01-start.eld
@@ -1 +1 @@
-#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n" 2 3 (erc-msg 
datestamp erc-ts 0 field erc-ti [...]
\ No newline at end of file
+#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n" 2 3 (erc-msg 
datestamp erc-ts 0 field erc-ti [...]
diff --git a/test/lisp/erc/resources/fill/snapshots/monospace-02-right.eld 
b/test/lisp/erc/resources/fill/snapshots/monospace-02-right.eld
index be3e2b33cfd..83394f2f639 100644
--- a/test/lisp/erc/resources/fill/snapshots/monospace-02-right.eld
+++ b/test/lisp/erc/resources/fill/snapshots/monospace-02-right.eld
@@ -1 +1 @@
-#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n" 2 3 (erc-msg 
datestamp erc-ts 0 field erc-ti [...]
\ No newline at end of file
+#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n" 2 3 (erc-msg 
datestamp erc-ts 0 field erc-ti [...]
diff --git a/test/lisp/erc/resources/fill/snapshots/monospace-03-left.eld 
b/test/lisp/erc/resources/fill/snapshots/monospace-03-left.eld
index 098257d0b49..1605628b29f 100644
--- a/test/lisp/erc/resources/fill/snapshots/monospace-03-left.eld
+++ b/test/lisp/erc/resources/fill/snapshots/monospace-03-left.eld
@@ -1 +1 @@
-#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n" 2 3 (erc-msg 
datestamp erc-ts 0 field erc-ti [...]
\ No newline at end of file
+#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n" 2 3 (erc-msg 
datestamp erc-ts 0 field erc-ti [...]
diff --git a/test/lisp/erc/resources/fill/snapshots/monospace-04-reset.eld 
b/test/lisp/erc/resources/fill/snapshots/monospace-04-reset.eld
index def97738ce6..84a1e34670c 100644
--- a/test/lisp/erc/resources/fill/snapshots/monospace-04-reset.eld
+++ b/test/lisp/erc/resources/fill/snapshots/monospace-04-reset.eld
@@ -1 +1 @@
-#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n" 2 3 (erc-msg 
datestamp erc-ts 0 field erc-ti [...]
\ No newline at end of file
+#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n" 2 3 (erc-msg 
datestamp erc-ts 0 field erc-ti [...]
diff --git a/test/lisp/erc/resources/fill/snapshots/spacing-01-mono.eld 
b/test/lisp/erc/resources/fill/snapshots/spacing-01-mono.eld
index 360b3dafafd..7a7e01de49d 100644
--- a/test/lisp/erc/resources/fill/snapshots/spacing-01-mono.eld
+++ b/test/lisp/erc/resources/fill/snapshots/spacing-01-mono.eld
@@ -1 +1 @@
-#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n<bob> This 
buffer is for text.\n*** one two th [...]
+#("\n\n\n[Thu Jan  1 1970]\n*** This server is in debug mode and is logging 
all user I/O. If you do not wish for everything you send to be readable by the 
server owner(s), please disconnect.[00:00]\n<alice> bob: come, you are a 
tedious fool: to the purpose. What was done to Elbow's wife, that he hath cause 
to complain of? Come me to what was done to her.\n<bob> alice: Either your 
unparagoned mistress is dead, or she's outprized by a trifle.\n<bob> This 
buffer is for text.\n*** one two th [...]
diff --git a/test/lisp/erc/resources/fill/snapshots/stamps-left-01.eld 
b/test/lisp/erc/resources/fill/snapshots/stamps-left-01.eld
index cd3537d3c94..bb248ffb28e 100644
--- a/test/lisp/erc/resources/fill/snapshots/stamps-left-01.eld
+++ b/test/lisp/erc/resources/fill/snapshots/stamps-left-01.eld
@@ -1 +1 @@
-#("\n\n[00:00]*** This server is in debug mode and is logging all user I/O. If 
you do not wish for everything you send to be readable by the server owner(s), 
please disconnect.\n[00:00]<alice> bob: come, you are a tedious fool: to the 
purpose. What was done to Elbow's wife, that he hath cause to complain of? Come 
me to what was done to her.\n[00:00]<bob> alice: Either your unparagoned 
mistress is dead, or she's outprized by a trifle.\n" 2 3 (erc-msg unknown 
erc-ts 0 display #3=(#5=(margi [...]
\ No newline at end of file
+#("\n\n[00:00]*** This server is in debug mode and is logging all user I/O. If 
you do not wish for everything you send to be readable by the server owner(s), 
please disconnect.\n[00:00]<alice> bob: come, you are a tedious fool: to the 
purpose. What was done to Elbow's wife, that he hath cause to complain of? Come 
me to what was done to her.\n[00:00]<bob> alice: Either your unparagoned 
mistress is dead, or she's outprized by a trifle.\n" 2 3 (erc-msg notice erc-ts 
0 display #3=(#5=(margin [...]