eval.c: fix circular cause

* eval.c (exc_setup_cause): always set cause of cause to get rid
  of circular references.  [ruby-core:78688] [Bug #13043]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57137 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

eval.c

@@ -457,6 +457,9 @@ exc_setup_cause(VALUE exc, VALUE cause)
 #endif
     if (!NIL_P(cause) && cause != exc) {
 	rb_ivar_set(exc, id_cause, cause);
+	if (!rb_ivar_defined(cause, id_cause)) {
+	    rb_ivar_set(cause, id_cause, Qnil);
+	}
     }
     return exc;
 }

test/ruby/test_exception.rb

@@ -777,6 +777,26 @@ end.join
     assert_equal({}, e.arg, bug)
   end
 
+  def test_circular_cause
+    bug13043 = '[ruby-core:78688] [Bug #13043]'
+    begin
+      begin
+        raise "error 1"
+      ensure
+        orig_error = $!
+        begin
+          raise "error 2"
+        rescue => err
+          raise orig_error
+        end
+      end
+    rescue => x
+    end
+    assert_equal(orig_error, x)
+    assert_equal(orig_error, err.cause)
+    assert_nil(orig_error.cause, bug13043)
+  end
+
   def test_anonymous_message
     assert_in_out_err([], "raise Class.new(RuntimeError), 'foo'", [], /foo\n/)
   end