Better handle traversing into subresources while resolving pointers.

This is .. ugly and duplicative. But more correct.

When traversing a JSON Pointer, we need to know when and if we're
entering a subresource, and this differs by spec (and has to do
with whether we've just entered a known keyword).

This will likely get less duplicative when #24 is done.

referencing/_core.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from collections.abc import Iterable, Iterator, Sequence
-from typing import Any, Callable, ClassVar, Generic
+from typing import Any, Callable, ClassVar, Generic, Protocol
 from urllib.parse import unquote, urldefrag, urljoin
 
 from attrs import evolve, field
@@ -13,6 +13,16 @@
 from referencing.typing import URI, Anchor as AnchorType, D, Mapping
 
 
+class _MaybeInSubresource(Protocol[D]):
+    def __call__(
+        self,
+        segments: Sequence[int | str],
+        resolver: Resolver[D],
+        subresource: Resource[D],
+    ) -> Resolver[D]:
+        ...
+
+
 @frozen
 class Specification(Generic[D]):
     """
@@ -32,6 +42,10 @@ class Specification(Generic[D]):
     #: the subresources themselves).
     subresources_of: Callable[[D], Iterable[D]]
 
+    #: While resolving a JSON pointer, conditionally enter a subresource
+    #: (if e.g. we have just entered a keyword whose value is a subresource)
+    maybe_in_subresource: _MaybeInSubresource[D]
+
     #: Retrieve the anchors contained in the given document.
     _anchors_in: Callable[
         [Specification[D], D],
@@ -63,6 +77,7 @@ def create_resource(self, contents: D) -> Resource[D]:
     id_of=lambda contents: None,
     subresources_of=lambda contents: [],
     anchors_in=lambda specification, contents: [],
+    maybe_in_subresource=lambda segments, resolver, subresource: resolver,
 )
 
 
@@ -156,6 +171,7 @@ def pointer(self, pointer: str, resolver: Resolver[D]) -> Resolved[D]:
                 if the pointer points to a location not present in the document
         """
         contents = self.contents
+        segments: list[int | str] = []
         for segment in unquote(pointer[1:]).split("/"):
             if isinstance(contents, Sequence):
                 segment = int(segment)
@@ -166,11 +182,12 @@ def pointer(self, pointer: str, resolver: Resolver[D]) -> Resolved[D]:
             except LookupError:
                 raise exceptions.PointerToNowhere(ref=pointer, resource=self)
 
-            # FIXME: this is slightly wrong, we need to know that we are
-            #        entering a subresource specifically, not just any mapping
-            if isinstance(contents, Mapping):
-                subresource = self._specification.create_resource(contents)  # type: ignore[reportUnknownArgumentType]  # noqa: E501
-                resolver = resolver.in_subresource(subresource)
+            segments.append(segment)
+            resolver = self._specification.maybe_in_subresource(
+                segments=segments,
+                resolver=resolver,
+                subresource=self._specification.create_resource(contents),  # type: ignore[reportUnknownArgumentType]  # noqa: E501
+            )
         return Resolved(contents=contents, resolver=resolver)  # type: ignore[reportUnknownArgumentType]  # noqa: E501
 
 

referencing/jsonschema.py

@@ -224,6 +224,29 @@ def subresources_of(contents: Schema) -> Iterable[ObjectSchema]:
     return subresources_of
 
 
+def _maybe_in_subresource(
+    in_value: Set[str] = frozenset(),
+    in_subvalues: Set[str] = frozenset(),
+    in_subarray: Set[str] = frozenset(),
+):
+    def maybe_in_subresource(
+        segments: Sequence[int | str],
+        resolver: _Resolver[Any],
+        subresource: Resource[Any],
+    ) -> _Resolver[Any]:
+        _segments = iter(segments)
+        for segment in _segments:
+            if segment in in_value:
+                continue
+            elif segment in in_subarray or segment in in_subvalues:
+                if next(_segments, None) is not None:
+                    continue
+            return resolver
+        return resolver.in_subresource(subresource)
+
+    return maybe_in_subresource
+
+
 DRAFT202012 = Specification(
     name="draft2020-12",
     id_of=_dollar_id,
@@ -250,6 +273,28 @@ def subresources_of(contents: Schema) -> Iterable[ObjectSchema]:
         },
     ),
     anchors_in=_anchor,
+    maybe_in_subresource=_maybe_in_subresource(
+        in_value={
+            "additionalProperties",
+            "contains",
+            "contentSchema",
+            "else",
+            "if",
+            "items",
+            "not",
+            "propertyNames",
+            "then",
+            "unevaluatedItems",
+            "unevaluatedProperties",
+        },
+        in_subarray={"allOf", "anyOf", "oneOf", "prefixItems"},
+        in_subvalues={
+            "$defs",
+            "dependentSchemas",
+            "patternProperties",
+            "properties",
+        },
+    ),
 )
 DRAFT201909 = Specification(
     name="draft2019-09",
@@ -277,6 +322,28 @@ def subresources_of(contents: Schema) -> Iterable[ObjectSchema]:
         },
     ),
     anchors_in=_anchor_2019,
+    maybe_in_subresource=_maybe_in_subresource(
+        in_value={
+            "additionalItems",
+            "additionalProperties",
+            "contains",
+            "contentSchema",
+            "else",
+            "if",
+            "not",
+            "propertyNames",
+            "then",
+            "unevaluatedItems",
+            "unevaluatedProperties",
+        },
+        in_subarray={"allOf", "anyOf", "oneOf"},
+        in_subvalues={
+            "$defs",
+            "dependentSchemas",
+            "patternProperties",
+            "properties",
+        },
+    ),
 )
 DRAFT7 = Specification(
     name="draft-07",
@@ -296,6 +363,20 @@ def subresources_of(contents: Schema) -> Iterable[ObjectSchema]:
         in_subvalues={"definitions", "patternProperties", "properties"},
     ),
     anchors_in=_legacy_anchor_in_dollar_id,
+    maybe_in_subresource=_maybe_in_subresource(
+        in_value={
+            "additionalItems",
+            "additionalProperties",
+            "contains",
+            "else",
+            "if",
+            "not",
+            "propertyNames",
+            "then",
+        },
+        in_subarray={"allOf", "anyOf", "oneOf"},
+        in_subvalues={"definitions", "patternProperties", "properties"},
+    ),
 )
 DRAFT6 = Specification(
     name="draft-06",
@@ -312,6 +393,17 @@ def subresources_of(contents: Schema) -> Iterable[ObjectSchema]:
         in_subvalues={"definitions", "patternProperties", "properties"},
     ),
     anchors_in=_legacy_anchor_in_dollar_id,
+    maybe_in_subresource=_maybe_in_subresource(
+        in_value={
+            "additionalItems",
+            "additionalProperties",
+            "contains",
+            "not",
+            "propertyNames",
+        },
+        in_subarray={"allOf", "anyOf", "oneOf"},
+        in_subvalues={"definitions", "patternProperties", "properties"},
+    ),
 )
 DRAFT4 = Specification(
     name="draft-04",
@@ -322,6 +414,11 @@ def subresources_of(contents: Schema) -> Iterable[ObjectSchema]:
         in_subvalues={"definitions", "patternProperties", "properties"},
     ),
     anchors_in=_legacy_anchor_in_id,
+    maybe_in_subresource=_maybe_in_subresource(
+        in_value={"additionalItems", "additionalProperties", "not"},
+        in_subarray={"allOf", "anyOf", "oneOf"},
+        in_subvalues={"definitions", "patternProperties", "properties"},
+    ),
 )
 DRAFT3 = Specification(
     name="draft-03",
@@ -332,6 +429,11 @@ def subresources_of(contents: Schema) -> Iterable[ObjectSchema]:
         in_subvalues={"definitions", "patternProperties", "properties"},
     ),
     anchors_in=_legacy_anchor_in_id,
+    maybe_in_subresource=_maybe_in_subresource(
+        in_value={"additionalItems", "additionalProperties"},
+        in_subarray={"extends"},
+        in_subvalues={"definitions", "patternProperties", "properties"},
+    ),
 )
 
 

referencing/tests/test_core.py

@@ -15,6 +15,12 @@
         )
         for name, each in contents.get("anchors", {}).items()
     ],
+    maybe_in_subresource=lambda segments, resolver, subresource: (
+        resolver.in_subresource(subresource)
+        if not len(segments) % 2
+        and all(each == "children" for each in segments[::2])
+        else resolver
+    ),
 )
 
 
@@ -534,6 +540,9 @@ def test_id_delegates_to_specification(self):
             id_of=lambda contents: "urn:fixedID",
             subresources_of=lambda contents: [],
             anchors_in=lambda specification, contents: [],
+            maybe_in_subresource=(
+                lambda segments, resolver, subresource: resolver
+            ),
         )
         resource = Resource(
             contents={"foo": "baz"},
@@ -816,6 +825,9 @@ def test_create_resource(self):
             id_of=lambda contents: "urn:fixedID",
             subresources_of=lambda contents: [],
             anchors_in=lambda specification, contents: [],
+            maybe_in_subresource=(
+                lambda segments, resolver, subresource: resolver
+            ),
         )
         resource = specification.create_resource(contents={"foo": "baz"})
         assert resource == Resource(