Preserve ERC prompt and its bounding markers

* lisp/erc/erc.el (erc--assert-input-bounds): Add possibly temporary
helper function to sync `process-mark' to `erc-insert-marker' in
server buffer.
(erc-display-line-1): Expect `erc-insert-marker' to always be
initialized.  Assert some essential invariants regarding insert
markers.
(erc-send-current-line): Delete typed input but not the prompt.
(erc-display-msg): Rework slightly to respect existing markers.
* test/lisp/erc/erc-dcc-tests.el
(erc-dcc-tests--dcc-handle-ctcp-send): Set insert marker.
* test/lisp/erc/erc-networks-tests.el
(erc-networks--rename-server-buffer--existing-live): Initialize
markers to appease `erc--assert-input-bounds'.
* test/lisp/erc/erc-tests.el (erc-ring-previous-command): Fix sloppy
mock.  (Bug#60936.)

3 files changed, 12 insertions, 4 deletions

diff --git a/test/lisp/erc/erc-dcc-tests.el b/test/lisp/erc/erc-dcc-tests.el
index fed86eff2c5..7fb5f82e784 100644
--- a/test/lisp/erc/erc-dcc-tests.el
+++ b/test/lisp/erc/erc-dcc-tests.el
@@ -60,6 +60,8 @@
             erc-input-marker (make-marker)
             erc-insert-marker (make-marker)
             erc-server-current-nick "dummy")
+      (erc-display-prompt)
+      (set-marker erc-insert-marker (pos-bol))
       (set-process-query-on-exit-flag erc-server-process nil)
       (should-not erc-dcc-list)
       (erc-ctcp-query-DCC erc-server-process
diff --git a/test/lisp/erc/erc-networks-tests.el b/test/lisp/erc/erc-networks-tests.el
index 96836c29aed..b9d216f217b 100644
--- a/test/lisp/erc/erc-networks-tests.el
+++ b/test/lisp/erc/erc-networks-tests.el
@@ -1475,10 +1475,16 @@
         (erc-mode)
         (setq erc-network 'FooNet
               erc-server-current-nick "tester"
-              erc-insert-marker (set-marker (make-marker) (point-max))
+              erc-insert-marker (make-marker)
+              erc-input-marker (make-marker)
               erc-server-process (erc-networks-tests--create-live-proc)
               erc-networks--id (erc-networks--id-create nil))
-        (should-not (erc-networks--rename-server-buffer erc-server-process))
+        (set-process-sentinel erc-server-process #'ignore)
+        (erc-display-prompt nil (point-max))
+        (set-marker erc-insert-marker (pos-bol))
+        (erc-display-message nil 'notice (current-buffer) "notice")
+        (with-silent-modifications
+          (should-not (erc-networks--rename-server-buffer erc-server-process)))
         (should (eq erc-active-buffer old-buf))
         (should-not (erc-server-process-alive))
         (should (string= (buffer-name) "irc.foonet.org"))
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index 795864a2cc2..b2f24aa718e 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -559,8 +559,8 @@
     ;;
     (cl-letf (((symbol-function 'erc-process-input-line)
                (lambda (&rest _)
-                 (insert-before-markers
-                  (erc-display-message-highlight 'notice "echo: one\n"))))
+                 (erc-display-message
+                  nil 'notice (current-buffer) "echo: one\n")))
               ((symbol-function 'erc-command-no-process-p)
                (lambda (&rest _) t)))
       (ert-info ("Create ring, populate, recall")