Don’t hard-loop on cycles in ‘read’ etc.

Problem for ‘read’ reported by Pip Cet in:
https://lists.gnu.org/r/emacs-devel/2019-08/msg00316.html
* src/fns.c (Frequire): Protect against circular current-load-list.
* src/lread.c (Fget_load_suffixes):
Protect against circular load-suffixes or load-file-rep-suffixes.
(Fload): Protect against circular loads-in-progress.
(openp): Protect against circular PATH and SUFFIXES.
(build_load_history): Protect against circular load-history or
current-load-list.
(readevalloop_eager_expand_eval): Protect against circular SUBFORMS.
(read1): Protect against circular data.
* test/src/lread-tests.el (lread-circular-hash): New test.

1 files changed, 3 insertions, 0 deletions

diff --git a/test/src/lread-tests.el b/test/src/lread-tests.el
index 82b75b195ca..ba5bfe0145d 100644
--- a/test/src/lread-tests.el
+++ b/test/src/lread-tests.el
@@ -220,4 +220,7 @@ literals (Bug#20852)."
                    (* most-positive-fixnum most-positive-fixnum)))
     (should (= n (string-to-number (format "%d." n))))))
 
+(ert-deftest lread-circular-hash ()
+  (should-error (read "#s(hash-table data #0=(#0# . #0#))")))
+
 ;;; lread-tests.el ends here