Fix fileio.c infloops on circular lists

Fix infinite loops in fileio.c when a circular list is the
value of after_insert_file_functions,
buffer-auto-save-file-format, buffer-file-format, or
write-region-annotate-functions.
* src/fileio.c (Finsert_file_contents, build_annotations):
Use FOR_EACH_TAIL to avoid infloop on circular lists.
(build_annotations): Use an EMACS_INT, not an int, to count
nesting level.
* test/src/fileio-tests.el:
(fileio-tests--circular-after-insert-file-functions): New test.

1 files changed, 9 insertions, 0 deletions

diff --git a/test/src/fileio-tests.el b/test/src/fileio-tests.el
index 98d3d6be763..2225897af8c 100644
--- a/test/src/fileio-tests.el
+++ b/test/src/fileio-tests.el
@@ -147,3 +147,12 @@ Also check that an encoding error can appear in a symlink."
       (should (file-name-absolute-p (concat "~" user-login-name suffix))))
     (unless (user-full-name "nosuchuser")
       (should (not (file-name-absolute-p (concat "~nosuchuser" suffix)))))))
+
+(ert-deftest fileio-tests--circular-after-insert-file-functions ()
+  "Test after-insert-file-functions as a circular list."
+  (let ((f (make-temp-file "fileio"))
+        (after-insert-file-functions (list 'identity)))
+    (setcdr after-insert-file-functions after-insert-file-functions)
+    (write-region "hello\n" nil f nil 'silent)
+    (should-error (insert-file-contents f) :type 'circular-list)
+    (delete-file f)))