Restore prompt correctly when reconnecting in ERC

* lisp/erc/erc.el (erc--initialize-markers): Commit 0d6c8d41ab7 "Use
overlay instead of text prop to hide ERC's prompt" introduced a bug
that caused the prompt to remain hidden upon reconnecting because the
stashed overlay would get clobbered by ERC's major-mode setup.
Binding its old value while unhiding fixes the issue.
* test/lisp/erc/erc-tests.el (erc-hide-prompt): Don't permanently set
the default value of `erc-hide-prompt'.
* test/lisp/erc/resources/erc-scenarios-common.el
(erc-scenarios-common--join-network-id): Add assertions for prompt
hiding and unhiding on reconnect.  (Bug#51082)

2 files changed, 22 insertions, 5 deletions

diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index 0d6ddf12380..912a85ad5e0 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -155,7 +155,9 @@
   (set-process-query-on-exit-flag erc-server-process nil))
 
 (ert-deftest erc-hide-prompt ()
-  (let (erc-kill-channel-hook erc-kill-server-hook erc-kill-buffer-hook)
+  (let ((erc-hide-prompt erc-hide-prompt)
+        ;;
+        erc-kill-channel-hook erc-kill-server-hook erc-kill-buffer-hook)
 
     (with-current-buffer (get-buffer-create "ServNet")
       (erc-tests--send-prep)
diff --git a/test/lisp/erc/resources/erc-scenarios-common.el b/test/lisp/erc/resources/erc-scenarios-common.el
index 802ccaeedaa..311d8a82d72 100644
--- a/test/lisp/erc/resources/erc-scenarios-common.el
+++ b/test/lisp/erc/resources/erc-scenarios-common.el
@@ -654,10 +654,17 @@ Bug#48598: 28.0.50; buffer-naming collisions involving bouncers in ERC."
       (with-current-buffer erc-server-buffer-foo (erc-cmd-JOIN "#chan"))
       (with-current-buffer (erc-d-t-wait-for 5 (get-buffer "#chan"))
         (funcall expect 5 "vile thing")
-        (erc-cmd-QUIT "")))
+        (erc-cmd-QUIT "")
 
-    (erc-d-t-wait-for 2 "Foonet connection deceased"
-      (not (erc-server-process-alive erc-server-buffer-foo)))
+        (ert-info ("Prompt hidden in channel buffer upon quitting")
+          (erc-d-t-wait-for 10 (erc--prompt-hidden-p))
+          (should (overlays-in erc-insert-marker erc-input-marker)))))
+
+    (with-current-buffer erc-server-buffer-foo
+      (ert-info ("Prompt hidden after process dies in server buffer")
+        (erc-d-t-wait-for 2 (not (erc-server-process-alive)))
+        (erc-d-t-wait-for 10 (erc--prompt-hidden-p))
+        (should (overlays-in erc-insert-marker erc-input-marker))))
 
     (should (equal erc-autojoin-channels-alist
                    (if foo-id '((oofnet "#chan")) '((foonet "#chan")))))
@@ -706,6 +713,10 @@ Bug#48598: 28.0.50; buffer-naming collisions involving bouncers in ERC."
         (setq erc-server-process-foo erc-server-process)
         (erc-d-t-wait-for 2 (eq erc-network 'foonet))
         (should (string= (buffer-name) (if foo-id "oofnet" "foonet")))
+
+        (ert-info ("Prompt unhidden")
+          (should-not (erc--prompt-hidden-p))
+          (should-not (overlays-in erc-insert-marker erc-input-marker)))
         (funcall expect 5 "foonet")))
 
     (ert-info ("#chan@foonet is clean, no cross-contamination")
@@ -713,7 +724,11 @@ Bug#48598: 28.0.50; buffer-naming collisions involving bouncers in ERC."
         (erc-d-t-wait-for 3 (eq erc-server-process erc-server-process-foo))
         (funcall expect 3 "<bob>")
         (erc-d-t-absent-for 0.1 "<joe>")
-        (funcall expect 20 "not given me")))
+        (funcall expect 30 "not given me")
+
+        (ert-info ("Prompt unhidden")
+          (should-not (erc--prompt-hidden-p))
+          (should-not (overlays-in erc-insert-marker erc-input-marker)))))
 
     (ert-info ("All #chan@barnet output received")
       (with-current-buffer chan-buf-bar