Let ?\LF signal an error (bug#55738)

As suggested by Stefan Monnier.

* src/lread.c (read_escape):
Signal an error for ?\LF since it cannot reasonably be intended.
* test/src/lread-tests.el (lread-escaped-lf): Update test.
* etc/NEWS: Announce.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/lread.c b/src/lread.c
index 4b7d38a8e6c..1d20470a8bf 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -2664,6 +2664,10 @@ read_escape (Lisp_Object readcharfun)
     case 'v':
       return '\v';
 
+    case '\n':
+      /* ?\LF is an error; it's probably a user mistake.  */
+      error ("Invalid escape character syntax");
+
     case 'M':
       c = READCHAR;
       if (c != '-')