Fix #49 (#70)

* Support external $ref with JSON Pointer fragment (issue #49)

Refs of the form 'file.yaml#/components/parameters/foo' previously
failed because the fragment was included in the file path. Now the
reference is split at '#', the external file is loaded, and the JSON
Pointer fragment is used to extract the correct sub-object.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Apply black formatting

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: RobertoPrevato

CHANGELOG.md

@@ -18,6 +18,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix [#47](https://github.com/Neoteroi/essentials-openapi/issues/47): remove `wordwrap`
   filters from all templates as they break links and mermaid chart code blocks in
   descriptions, reported by @ElementalWarrior.
+- Fix [#49](https://github.com/Neoteroi/essentials-openapi/issues/49): support `$ref`
+  values of the form `file.yaml#/fragment/path` (external file with JSON Pointer
+  fragment), reported by @mbklein.
 
 ## [1.3.0] - 2025-11-19
 

openapidocs/mk/v3/__init__.py

@@ -275,18 +275,46 @@ def _handle_obj_ref(self, obj, source_path):
         Handles a dictionary containing a $ref property, resolving the reference if it
         is to a file. This is used to read specification files when they are split into
         multiple items.
+
+        Supports three forms:
+        - ``#/internal/ref``                    — internal ref, left as-is
+        - ``path/to/file.yaml``                 — entire external file
+        - ``path/to/file.yaml#/fragment/path``  — fragment within an external file
         """
         assert isinstance(obj, dict)
         if "$ref" in obj:
             reference = obj["$ref"]
             if isinstance(reference, str) and not reference.startswith("#/"):
-                referred_file = Path(os.path.abspath(source_path / reference))
+                # Split off an optional JSON Pointer fragment (#/...)
+                if "#" in reference:
+                    file_part, fragment = reference.split("#", 1)
+                else:
+                    file_part, fragment = reference, ""
+
+                referred_file = Path(os.path.abspath(source_path / file_part))
 
                 if referred_file.exists():
                     logger.debug("Handling $ref source: %s", reference)
                 else:
                     raise OpenAPIFileNotFoundError(reference, referred_file)
+
                 sub_fragment = read_from_source(str(referred_file))
+
+                if fragment:
+                    # Resolve the JSON Pointer (RFC 6901) into the loaded data.
+                    # Strip the leading '/' then split on '/'.
+                    keys = fragment.lstrip("/").split("/")
+                    for key in keys:
+                        if (
+                            not isinstance(sub_fragment, dict)
+                            or key not in sub_fragment
+                        ):
+                            raise OpenAPIDocumentationHandlerError(
+                                f"Cannot resolve fragment '{fragment}' in {referred_file}: "
+                                f"key '{key}' not found."
+                            )
+                        sub_fragment = sub_fragment[key]
+
                 return self._transform_data(sub_fragment, referred_file.parent)
             else:
                 return obj

tests/res/spec-fragments/openapi.yaml

@@ -0,0 +1,19 @@
+---
+openapi: 3.0.0
+info:
+  title: Fragment Refs API
+  description: API using external $ref with fragment pointers
+  version: v1
+paths:
+  /collections:
+    get:
+      operationId: getCollections
+      summary: Get collections
+      tags:
+        - Collection
+      parameters:
+        - $ref: "./types.yaml#/components/parameters/page"
+        - $ref: "./types.yaml#/components/parameters/size"
+      responses:
+        "200":
+          $ref: "./types.yaml#/components/responses/SearchResponse"

tests/res/spec-fragments/types.yaml

@@ -0,0 +1,33 @@
+---
+components:
+  parameters:
+    page:
+      name: page
+      in: query
+      description: Page number
+      required: false
+      schema:
+        type: integer
+        default: 1
+    size:
+      name: size
+      in: query
+      description: Page size
+      required: false
+      schema:
+        type: integer
+        default: 20
+  responses:
+    SearchResponse:
+      description: Successful search response
+      content:
+        application/json:
+          schema:
+            type: object
+            properties:
+              total:
+                type: integer
+              items:
+                type: array
+                items:
+                  type: object

tests/test_mk_v3.py

@@ -41,6 +41,26 @@ def test_v3_markdown_gen_split_file():
     assert compatible_str(html, expected_result)
 
 
+def test_v3_external_ref_with_fragment():
+    """
+    Regression test for https://github.com/Neoteroi/essentials-openapi/issues/49
+    $ref values of the form 'file.yaml#/path/to/item' should resolve the fragment
+    within the external file rather than failing with a file-not-found error.
+    """
+    source = get_resource_file_path("spec-fragments/openapi.yaml")
+    data = get_file_yaml("spec-fragments/openapi.yaml")
+
+    handler = OpenAPIV3DocumentationHandler(data, source=source)
+    output = handler.write()
+
+    # Parameters resolved from types.yaml#/components/parameters/...
+    assert "<code>page</code>" in output
+    assert "<code>size</code>" in output
+    # Response resolved from types.yaml#/components/responses/SearchResponse
+    assert '=== "200 OK"' in output
+    assert '"total"' in output
+
+
 def test_file_ref_raises_for_missing_file():
     with pytest.raises(OpenAPIFileNotFoundError):
         OpenAPIV3DocumentationHandler(