disable DOM API when using ARC (ref #85)

test/tests.nim

@@ -4,4 +4,8 @@
 #    See the file "copying.txt", included in this
 #    distribution, for details about the copyright.
 
-import tlex, tjson, tserialization, tdom, tparser, tquickstart, tannotations
+
+import tlex, tjson, tserialization, tparser, tquickstart, tannotations
+
+when not defined(gcArc) or defined(gcOrc):
+  import tdom

yaml.nim

@@ -38,8 +38,14 @@
 ## * The hints API in `hints <yaml.hints.html>`_ provides a simple proc for
 ##   guessing the type of a scalar value.
 
-import yaml / [dom, hints, parser, presenter, annotations,
+import yaml / [hints, parser, presenter, annotations,
                serialization, stream, taglib, tojson]
 
-export dom, hints, parser, presenter, annotations,
+when not defined(gcArc) or defined(gcOrc):
+  # YAML DOM may contain cycles and therefore will leak memory if used with
+  # ARC but without ORC. In that case it won't be available.
+  import yaml/dom
+  export dom
+
+export hints, parser, presenter, annotations,
        serialization, stream, taglib, tojson

yaml/dom.nim

@@ -23,6 +23,9 @@ import tables, streams, hashes, sets, strutils
 import data, stream, taglib, serialization, private/internal, parser,
        presenter
 
+when defined(gcArc) and not defined(gcOrc):
+  {.error: "NimYAML's DOM API only supports ORC because ARC can't deal with cycles".}
+
 when defined(nimNoNil):
     {.experimental: "notnil".}
 type