Fixes and improvements to DOM API.

* added loadFlattened. Fixes #117
 * fixed an error where recursive nodes were not loaded
   properly into YamlNodes.
 * made dump with asNone raise an error when a cycle is
   encountered, instead of running into an endless loop.

yaml/dom.nim

@@ -19,7 +19,7 @@
 ## The ``YamlNode`` objects in the DOM can be used similarly to the ``JsonNode``
 ## objects of Nim's `json module <http://nim-lang.org/docs/json.html>`_.
 
-import tables, streams, hashes, sets, strutils
+import std / [tables, streams, hashes, sets, strutils]
 import data, stream, taglib, serialization, private/internal, parser,
        presenter
 
@@ -174,6 +174,7 @@ proc constructChild*(s: var YamlStream, c: ConstructionContext,
                       fields: newTable[YamlNode, YamlNode](),
                       mapStyle: start.mapStyle,
                       startPos: start.startPos, endPos: start.endPos)
+    addAnchor(c, start.mapProperties.anchor)
     while s.peek().kind != yamlEndMap:
       var
         key: YamlNode = nil
@@ -184,28 +185,27 @@ proc constructChild*(s: var YamlStream, c: ConstructionContext,
         raise newException(YamlConstructionError,
             "Duplicate key: " & $key)
     discard s.next()
-    addAnchor(c, start.mapProperties.anchor)
   of yamlStartSeq:
     result = YamlNode(tag: start.seqProperties.tag,
                       kind: ySequence,
                       elems: newSeq[YamlNode](),
                       seqStyle: start.seqStyle,
                       startPos: start.startPos, endPos: start.endPos)
+    addAnchor(c, start.seqProperties.anchor)
     while s.peek().kind != yamlEndSeq:
       var item: YamlNode = nil
       constructChild(s, c, item)
       result.elems.add(item)
-    addAnchor(c, start.seqProperties.anchor)
     discard s.next()
   of yamlScalar:
     result = YamlNode(tag: start.scalarProperties.tag,
                       kind: yScalar, scalarStyle: start.scalarStyle,
                       startPos: start.startPos, endPos: start.endPos)
+    addAnchor(c, start.scalarProperties.anchor)
     when defined(gcArc) or defined(gcOrc):
       result.content = move start.scalarContent
     else:
       shallowCopy(result.content, start.scalarContent)
-    addAnchor(c, start.scalarProperties.anchor)
   of yamlAlias:
     result = cast[YamlNode](c.refs.getOrDefault(start.aliasTarget).p)
   else: internalError("Malformed YamlStream")
@@ -342,3 +342,26 @@ iterator mpairs*(node: var YamlNode):
   ## *yMapping*. Values can be modified.
   doAssert node.kind == yMapping
   for key, value in node.fields.mpairs: yield (key, value)
+
+proc loadFlattened*[K](input: Stream | string, target: var K)
+    {.raises: [YamlConstructionError, YamlSerializationError, IOError, OSError,
+               YamlParserError].} =
+  ## Replaces all aliases with the referenced nodes in the input, then loads
+  ## the resulting YAML into K. Can be used when anchors & aliases are used like
+  ## variables in the input, to avoid having to define `ref` types for the
+  ## anchored data.
+  var node: YamlNode
+  load(input, node)
+  var stream = represent(node, tsNone, asNone)
+  try:
+    var e = stream.next()
+    yAssert(e.kind == yamlStartStream)
+    construct(stream, target)
+    e = stream.next()
+    yAssert(e.kind == yamlEndStream)
+  except YamlStreamError:
+    let e = (ref YamlStreamError)(getCurrentException())
+    if e.parent of IOError: raise (ref IOError)(e.parent)
+    if e.parent of OSError: raise (ref OSError)(e.parent)
+    elif e.parent of YamlParserError: raise (ref YamlParserError)(e.parent)
+    else: internalError("Unexpected exception: " & $e.parent.name)

yaml/presenter.nim

@@ -46,10 +46,10 @@ type
   AnchorStyle* = enum
     ## How ref object should be serialized.
     ##
-    ## - ``asNone``: No anchors will be outputted. Values present at
+    ## - ``asNone``: No anchors will be written. Values present at
     ##   multiple places in the content that should be serialized will be
     ##   fully serialized at every occurence. If the content is cyclic, this
-    ##   will lead to an endless loop!
+    ##   will raise a YamlSerializationError.
     ## - ``asTidy``: Anchors will only be generated for objects that
     ##   actually occur more than once in the content to be serialized.
     ##   This is a bit slower and needs more memory than ``asAlways``.

yaml/serialization.nim

@@ -16,7 +16,7 @@
 ## type. Please consult the serialization guide on the NimYAML website for more
 ## information.
 
-import tables, typetraits, strutils, macros, streams, times, parseutils, options
+import std / [tables, typetraits, strutils, macros, streams, times, parseutils, options]
 import data, parser, taglib, presenter, stream, private/internal, hints, annotations
 export data, stream, macros, annotations, options
   # *something* in here needs externally visible `==`(x,y: AnchorId),
@@ -1251,21 +1251,26 @@ proc representChild*[T](value: seq[T], ts: TagStyle, c: SerializationContext) =
 
 proc representChild*[O](value: ref O, ts: TagStyle, c: SerializationContext) =
   if isNil(value): c.put(scalarEvent("~", yTagNull))
-  elif c.style == asNone: representChild(value[], ts, c)
   else:
-    var val: tuple[a: Anchor, referenced: bool]
     let p = cast[pointer](value)
-    if c.refs.hasKey(p):
-      val = c.refs.getOrDefault(p)
-      yAssert(val.a != yAnchorNone)
-      if not val.referenced:
-        c.refs[p] = (val.a, true)
-      c.put(aliasEvent(val.a))
-      return
-    if c.style != asNone:
-      val = (c.nextAnchorId.Anchor, false)
-      c.refs[p] = val
-      nextAnchor(c.nextAnchorId, len(c.nextAnchorId) - 1)
+    # when c.style == asNone, `referenced` is used as indicator that we are
+    # currently in the process of serializing this node. This enables us to
+    # detect cycles and raise an error.
+    var val = c.refs.getOrDefault(p, (c.nextAnchorId.Anchor, c.style == asNone))
+    if val.a != c.nextAnchorId.Anchor:
+      if c.style == asNone:
+        if val.referenced:
+          raise newException(YamlSerializationError,
+              "tried to serialize cyclic graph with asNone")
+      else:
+        val = c.refs.getOrDefault(p)
+        yAssert(val.a != yAnchorNone)
+        if not val.referenced:
+          c.refs[p] = (val.a, true)
+        c.put(aliasEvent(val.a))
+        return
+    c.refs[p] = val
+    nextAnchor(c.nextAnchorId, len(c.nextAnchorId) - 1)
     let
       childTagStyle = if ts == tsAll: tsAll else: tsRootOnly
       origPut = c.put
@@ -1273,19 +1278,20 @@ proc representChild*[O](value: ref O, ts: TagStyle, c: SerializationContext) =
       var ex = e
       case ex.kind
       of yamlStartMap:
-        ex.mapProperties.anchor = val.a
+        if c.style != asNone: ex.mapProperties.anchor = val.a
         if ts == tsNone: ex.mapProperties.tag = yTagQuestionMark
       of yamlStartSeq:
-        ex.seqProperties.anchor = val.a
+        if c.style != asNone: ex.seqProperties.anchor = val.a
         if ts == tsNone: ex.seqProperties.tag = yTagQuestionMark
       of yamlScalar:
-        ex.scalarProperties.anchor = val.a
+        if c.style != asNone: ex.scalarProperties.anchor = val.a
         if ts == tsNone and guessType(ex.scalarContent) != yTypeNull:
           ex.scalarProperties.tag = yTagQuestionMark
       else: discard
       c.put = origPut
       c.put(ex)
     representChild(value[], childTagStyle, c)
+    if c.style == asNone: c.refs[p] = (val.a, false)
 
 proc representChild*[T](value: Option[T], ts: TagStyle,
     c: SerializationContext) =