Upstream creating a Resolver with a specific root resource.

Maybe there's some way to collapse this but for now, saves
downstream having to assign some default base URI for the
(possibly-not-internally-identified) resource.

Author: Julian

referencing/_core.py

@@ -371,6 +371,19 @@ def resolver(self, base_uri: URI = "") -> Resolver[D]:
         """
         return Resolver(base_uri=base_uri, registry=self)
 
+    def resolver_with_root(self, resource: Resource[D]) -> Resolver[D]:
+        """
+        Return a `Resolver` with a specific root resource.
+
+        The resource must have an internal identifier (e.g. for a JSON Schema
+        resource in recent versions, an ``$id`` keyword).
+        """
+        uri = resource.id() or ""
+        return Resolver(
+            base_uri=uri,
+            registry=self.with_resource(uri, resource),
+        )
+
 
 @frozen
 class Resolved(Generic[D]):

referencing/tests/test_core.py

@@ -425,6 +425,23 @@ def retrieve(uri):
         registry = Registry(retrieve=retrieve).with_resource("urn:root", root)
         assert registry.crawl()["urn:child"] == child
 
+    def test_resolver(self):
+        one = Resource.opaque(contents={})
+        registry = Registry({"http://example.com": one})
+        resolver = registry.resolver(base_uri="http://example.com")
+        assert resolver.lookup("#").contents == {}
+
+    def test_resolver_with_root_identified(self):
+        root = ID_AND_CHILDREN.create_resource({"ID": "http://example.com"})
+        resolver = Registry().resolver_with_root(root)
+        assert resolver.lookup("http://example.com").contents == root.contents
+        assert resolver.lookup("#").contents == root.contents
+
+    def test_resolver_with_root_unidentified(self):
+        root = Resource.opaque(contents={})
+        resolver = Registry().resolver_with_root(root)
+        assert resolver.lookup("#").contents == root.contents
+
     def test_repr(self):
         one = Resource.opaque(contents={})
         two = ID_AND_CHILDREN.create_resource({"foo": "bar"})