move reference to converter

asdf/core/_converters/reference.py

@@ -0,0 +1,18 @@
+from asdf.extension import Converter
+
+
+class ReferenceConverter(Converter):
+    tags = []
+    types = ["asdf.reference.Reference"]
+
+    def to_yaml_tree(self, obj, tag, ctx):
+        from asdf.generic_io import relative_uri
+
+        uri = relative_uri(ctx.url, obj._uri) if ctx.url is not None else obj._uri
+        return {"$ref": uri}
+
+    def from_yaml_tree(self, node, tag, ctx):
+        raise NotImplementedError()
+
+    def select_tag(self, obj, tags, ctx):
+        return None

asdf/core/_extensions.py

@@ -3,6 +3,7 @@
 from ._converters.complex import ComplexConverter
 from ._converters.constant import ConstantConverter
 from ._converters.external_reference import ExternalArrayReferenceConverter
+from ._converters.reference import ReferenceConverter
 from ._converters.tree import (
     AsdfObjectConverter,
     ExtensionMetadataConverter,
@@ -21,6 +22,7 @@
     HistoryEntryConverter(),
     SoftwareConverter(),
     SubclassMetadataConverter(),
+    ReferenceConverter(),
 ]
 
 

asdf/extension/_converter.py

@@ -208,6 +208,11 @@ def __init__(self, delegate, extension):
         self._tags = sorted(relevant_tags)
 
         self._types = []
+
+        if not len(self._tags) and not hasattr(delegate, "select_tag"):
+            # this converter supports no tags so don't inspect the types
+            return
+
         for typ in delegate.types:
             if isinstance(typ, (str, type)):
                 self._types.append(typ)

asdf/reference.py

@@ -11,7 +11,7 @@
 
 import numpy as np
 
-from . import _types, generic_io, treeutil, util
+from . import generic_io, treeutil, util
 from .util import patched_urllib_parse
 
 __all__ = ["resolve_fragment", "Reference", "find_references", "resolve_references", "make_reference"]
@@ -42,9 +42,7 @@ def resolve_fragment(tree, pointer):
     return tree
 
 
-class Reference(_types._AsdfType):
-    yaml_tag = "tag:yaml.org,2002:map"
-
+class Reference:
     def __init__(self, uri, base_uri=None, asdffile=None, target=None):
         self._uri = uri
         if asdffile is not None:
@@ -105,15 +103,6 @@ def __call__(self, **kwargs):
     def __contains__(self, item):
         return item in self._get_target()
 
-    @classmethod
-    def to_tree(cls, data, ctx):
-        uri = generic_io.relative_uri(ctx.uri, data._uri) if ctx.uri is not None else data._uri
-        return {"$ref": uri}
-
-    @classmethod
-    def validate(cls, data):
-        pass
-
 
 def find_references(tree, ctx):
     """