Handle #@00 in new reader in a compatible way (bug#63722)

This was a regression from Emacs 28.

* src/lread.c (skip_lazy_string, read0): Make #@00 read as nil, which
is a quirk from the old reader that we preserve for compatibility.
* test/src/lread-tests.el (lread-skip-to-eof): Verify it.

Reported by Richard Newton.

1 files changed, 16 insertions, 0 deletions

diff --git a/test/src/lread-tests.el b/test/src/lread-tests.el
index 459a06a39b6..7d885abf364 100644
--- a/test/src/lread-tests.el
+++ b/test/src/lread-tests.el
@@ -339,4 +339,20 @@ literals (Bug#20852)."
         (should (byte-code-function-p f))
         (should (equal (aref f 4) "My little\ndoc string\nhere"))))))
 
+(ert-deftest lread-skip-to-eof ()
+  ;; Check the special #@00 syntax that, for compatibility, reads as
+  ;; nil while absorbing the remainder of the input.
+  (with-temp-buffer
+    (insert "#@00 and the rest\n"
+            "should be ignored) entirely\n")
+    (goto-char (point-min))
+    (should (equal (read (current-buffer)) nil))
+    (should (eobp))
+    ;; Add an unbalanced bracket to the beginning and try again;
+    ;; we should get an error.
+    (goto-char (point-min))
+    (insert "( ")
+    (goto-char (point-min))
+    (should-error (read (current-buffer)) :type 'end-of-file)))
+
 ;;; lread-tests.el ends here