Detect loop in error_trace.

* eval.c (error_trace): If a form has itself as its macro
ancestor, bail the loop. (This only happens in deliberately
contrived pathological cases, useful for testing).

1 files changed, 3 insertions, 0 deletions

diff --git a/eval.c b/eval.c
index 07791880..3ab401e4 100644
--- a/eval.c
+++ b/eval.c
@@ -267,6 +267,9 @@ void error_trace(val exsym, val exvals, val out_stream, val prefix)
           format(out_stream, lit("~a whose location is unavailable\n"), prefix,
                  nao);
       }
+
+      if (origin == last)
+        break;
     }
   }