Fix regression in erc-send-input-line

* lisp/erc/erc.el (erc-send-input-line): Restore remedial single-space
padding to ensure empty messages typed at the prompt without an
explicit /msg aren't rejected by the server.  This behavior is only
noticeable when `erc-send-whitespace-lines' is active.

* test/lisp/erc/erc-tests.el (erc-process-input-line): Add trailing
newline to more correctly simulate how it's actually called by
`erc-send-input'. (Bug#50008)

2 files changed, 7 insertions, 5 deletions

diff --git a/lisp/erc/erc.el b/lisp/erc/erc.el
index 1c221a9cb13..971d3f426fc 100644
--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -2992,6 +2992,8 @@ for special purposes (see erc-dcc.el).")
 
 (defun erc-send-input-line (target line &optional force)
   "Send LINE to TARGET."
+  (when (string= line "\n")
+    (setq line " \n"))
   (erc-message "PRIVMSG" (concat target " " line) force))
 
 (defun erc-get-arglist (fun)
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index 618d7eeea02..afe9cc7b8cb 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -643,19 +643,19 @@
         (ert-info ("Implicit cmd via `erc-send-input-line-function'")
 
           (ert-info ("Baseline")
-            (erc-process-input-line "hi")
+            (erc-process-input-line "hi\n")
             (should (equal (pop erc-server-flood-queue)
                            '("PRIVMSG #chan :hi\r\n" . utf-8))))
 
           (ert-info ("Spaces preserved")
-            (erc-process-input-line "hi you")
+            (erc-process-input-line "hi you\n")
             (should (equal (pop erc-server-flood-queue)
                            '("PRIVMSG #chan :hi you\r\n" . utf-8))))
 
-          (ert-info ("Empty line transmitted without injected-space kludge")
-            (erc-process-input-line "")
+          (ert-info ("Empty line transmitted with injected-space kludge")
+            (erc-process-input-line "\n")
             (should (equal (pop erc-server-flood-queue)
-                           '("PRIVMSG #chan :\r\n" . utf-8))))
+                           '("PRIVMSG #chan : \r\n" . utf-8))))
 
           (should-not calls))))))