1 files changed, 18 insertions, 0 deletions

diff --git a/test/src/data-tests.el b/test/src/data-tests.el
index bc77a7be94e..a9d48e29a8a 100644
--- a/test/src/data-tests.el
+++ b/test/src/data-tests.el
@@ -669,4 +669,22 @@ comparing the subr with a much slower lisp implementation."
   (should (= (lsh -1 -1) most-positive-fixnum))
   (should-error (lsh (1- most-negative-fixnum) -1)))
 
+(ert-deftest data-tests-make-local-forwarded-var () ;bug#34318
+  ;; Boy, this bug is tricky to trigger.  You need to:
+  ;; - call make-local-variable on a forwarded var (i.e. one that
+  ;;   has a corresponding C var linked via DEFVAR_(LISP|INT|BOOL))
+  ;; - cause the C code to modify this variable from the C side of the
+  ;;   forwarding, but this needs to happen before the var is accessed
+  ;;   from the Lisp side and before we switch to another buffer.
+  ;; The trigger in bug#34318 doesn't exist any more because the C code has
+  ;; changes.  Instead I found the trigger below.
+  (with-temp-buffer
+    (setq last-coding-system-used 'bug34318)
+    (make-local-variable 'last-coding-system-used)
+    ;; This should set last-coding-system-used to `no-conversion'.
+    (decode-coding-string "hello" nil)
+    (should (equal (list last-coding-system-used
+                         (default-value 'last-coding-system-used))
+                   '(no-conversion bug34318)))))
+
 ;;; data-tests.el ends here