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, 6 insertions, 3 deletions

diff --git a/src/fns.c b/src/fns.c
index 6c47b3e5b1c..b606d6299ca 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -2950,9 +2950,12 @@ suppressed.  */)
      But not more than once in any file,
      and not when we aren't loading or reading from a file.  */
   if (!from_file)
-    for (tem = Vcurrent_load_list; CONSP (tem); tem = XCDR (tem))
-      if (NILP (XCDR (tem)) && STRINGP (XCAR (tem)))
-        from_file = 1;
+    {
+      Lisp_Object tail = Vcurrent_load_list;
+      FOR_EACH_TAIL_SAFE (tail)
+        if (NILP (XCDR (tail)) && STRINGP (XCAR (tail)))
+          from_file = true;
+    }
 
   if (from_file)
     {