made anchor resolution during deserialization safer

test/tlex.nim

@@ -211,7 +211,7 @@ suite "Lexer":
                  pl("bar baz"), dirE(), i(0), pl("derp"), e())
 
   test "Sequence with compact maps":
-    assertEquals("""- a: drzw\n- b""", i(0), ss(), pl("a"), mv(), pl("drzw"), i(0), ss(), pl("b"), e())
+    assertEquals("- a: drzw\n- b", i(0), si(), pl("a"), mv(), pl("drzw"), i(0), si(), pl("b"), e())
 
   test "Empty lines":
     assertEquals("""block: foo

yaml/data.nim

@@ -272,14 +272,3 @@ proc `$`*(event: Event): string {.raises: [].} =
     of ssFolded: result &= " >"
     result &= yamlTestSuiteEscape(event.scalarContent)
   of yamlAlias: result = "=ALI *" & $event.aliasTarget
-
-type
-  TypeID* = int ## unique ID of a type
-
-var nextTypeID {.compileTime.}: TypeID
-
-proc typeID*(T:typedesc): TypeID =
-  const id = nextTypeID
-  static:
-    inc nextTypeID
-  return id

yaml/dom.nim

@@ -138,7 +138,7 @@ proc composeNode(s: var YamlStream, tagLib: TagLibrary,
   template addAnchor(c: ConstructionContext, target: Anchor) =
     if target != yAnchorNone:
       yAssert(not c.refs.hasKey(target))
-      c.refs[target] = (id: typeID(YamlNode), p: cast[pointer](result))
+      c.refs[target] = (tag: yamlTag(YamlNode), p: cast[pointer](result))
 
   var start: Event
   shallowCopy(start, s.next())

yaml/serialization.nim

@@ -32,7 +32,7 @@ type
 
   ConstructionContext* = ref object
     ## Context information for the process of constructing Nim values from YAML.
-    refs*: Table[Anchor, tuple[id: TypeID, p: pointer]]
+    refs*: Table[Anchor, tuple[tag: Tag, p: pointer]]
 
   YamlConstructionError* = object of YamlLoadingError
     ## Exception that may be raised when constructing data objects from a
@@ -86,7 +86,7 @@ proc representChild*[O](value: O, ts: TagStyle, c: SerializationContext)
 
 proc newConstructionContext*(): ConstructionContext =
   new(result)
-  result.refs = initTable[Anchor, tuple[id: TypeID, p: pointer]]()
+  result.refs = initTable[Anchor, tuple[tag: Tag, p: pointer]]()
 
 proc newSerializationContext*(s: AnchorStyle,
     putImpl: proc(e: Event) {.raises: [], closure.}):
@@ -1223,14 +1223,18 @@ proc constructChild*[O](s: var YamlStream, c: ConstructionContext,
       discard s.next()
       return
   elif e.kind == yamlAlias:
-    result = cast[ref O](c.refs.getOrDefault(e.aliasTarget).p)
+    let val = c.refs.getOrDefault(e.aliasTarget)
+    if val.tag != yamlTag(O):
+      raise constructionError(s, e.startPos,
+        "alias node refers to object of incompatible type")
+    result = cast[ref O](val.p)
     discard s.next()
     return
   new(result)
   template removeAnchor(anchor: var Anchor) {.dirty.} =
     if anchor != yAnchorNone:
       yAssert(not c.refs.hasKey(anchor))
-      c.refs[anchor] = (0, cast[pointer](result))
+      c.refs[anchor] = (yamlTag(O), cast[pointer](result))
       anchor = yAnchorNone
 
   case e.kind