Add a way to drop resources from a registry.

Will be needed if/when #19 is done.

Author: Julian

referencing/_core.py

@@ -246,6 +246,22 @@ def __repr__(self) -> str:
             summary = f"{pluralized}"
         return f"<Registry ({size} {summary})>"
 
+    def remove(self, uri: URI):
+        """
+        Return a registry with the resource identified by a given URI removed.
+        """
+        if uri not in self._resources:
+            raise exceptions.NoSuchResource(ref=uri)
+
+        return evolve(
+            self,
+            resources=self._resources.remove(uri),
+            uncrawled=self._uncrawled.discard(uri),
+            anchors=pmap(
+                (k, v) for k, v in self._anchors.items() if k[0] != uri
+            ),
+        )
+
     def anchor(self, uri: URI, name: str):
         """
         Retrieve the given anchor, which must already have been found.

referencing/tests/test_core.py

@@ -338,6 +338,48 @@ def bar_retrieve(uri):
         with pytest.raises(Exception, match="conflict.*retriev"):  # noqa: B017
             first.combine(second, third)
 
+    def test_remove(self):
+        one = Resource.opaque(contents={})
+        two = ID_AND_CHILDREN.create_resource({"foo": "bar"})
+        registry = Registry({"urn:foo": one, "urn:bar": two})
+        assert registry.remove("urn:foo") == Registry({"urn:bar": two})
+
+    def test_remove_uncrawled(self):
+        one = Resource.opaque(contents={})
+        two = ID_AND_CHILDREN.create_resource({"foo": "bar"})
+        registry = Registry().with_resources(
+            [("urn:foo", one), ("urn:bar", two)],
+        )
+        assert registry.remove("urn:foo") == Registry().with_resource(
+            "urn:bar",
+            two,
+        )
+
+    def test_remove_with_anchors(self):
+        one = Resource.opaque(contents={})
+        two = ID_AND_CHILDREN.create_resource({"anchors": {"foo": "bar"}})
+        registry = (
+            Registry()
+            .with_resources(
+                [("urn:foo", one), ("urn:bar", two)],
+            )
+            .crawl()
+        )
+        assert (
+            registry.remove("urn:bar")
+            == Registry()
+            .with_resource(
+                "urn:foo",
+                one,
+            )
+            .crawl()
+        )
+
+    def test_remove_nonexistent_uri(self):
+        with pytest.raises(exceptions.NoSuchResource) as e:
+            Registry().remove("urn:doesNotExist")
+        assert e.value == exceptions.NoSuchResource(ref="urn:doesNotExist")
+
     def test_repr(self):
         one = Resource.opaque(contents={})
         two = ID_AND_CHILDREN.create_resource({"foo": "bar"})