Fix relative URL refs with path-only root ids (#3085)

Author: koxudaxi

src/datamodel_code_generator/reference.py

@@ -627,7 +627,7 @@ def add_id(self, id_: str, path: Sequence[str]) -> None:
         """Register an identifier mapping to a resolved reference path."""
         self.ids["/".join(self.current_root)][id_] = self.resolve_ref(path)
 
-    def resolve_ref(self, path: Sequence[str] | str) -> str:  # noqa: PLR0911, PLR0912, PLR0914
+    def resolve_ref(self, path: Sequence[str] | str) -> str:  # noqa: PLR0911, PLR0912, PLR0914, PLR0915
         """Resolve a reference path to its canonical form."""
         joined_path = path if isinstance(path, str) else self.join_path(tuple(path))
         if joined_path == "#":
@@ -679,7 +679,9 @@ def resolve_ref(self, path: Sequence[str] | str) -> str:  # noqa: PLR0911, PLR09
         if self.base_url:
             from .http import join_url  # noqa: PLC0415
 
-            effective_base = self.root_id or self.base_url
+            effective_base = self.base_url
+            if self.root_id:
+                effective_base = self.root_id if is_url(self.root_id) else join_url(self.base_url, self.root_id)
             joined_url = join_url(effective_base, ref)
             if "#" in joined_url:
                 return joined_url

tests/main/jsonschema/test_main_jsonschema.py

@@ -992,6 +992,73 @@ def test_main_root_id_jsonschema_with_absolute_local_file(output_file: Path) ->
     )
 
 
+def test_main_url_with_relative_root_id_resolves_relative_refs(mocker: MockerFixture, tmp_path: Path) -> None:
+    """Test --url input keeps resolving relative refs remotely when root $id is path-only."""
+    main_response = mocker.Mock()
+    main_response.status_code = 200
+    main_response.headers = {}
+    main_response.text = json.dumps({
+        "$id": "/schemas/v1/main.schema.json",
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "title": "Main",
+        "type": "object",
+        "properties": {
+            "sub": {
+                "$ref": "sub.schema.json",
+            }
+        },
+        "required": ["sub"],
+    })
+    sub_response = mocker.Mock()
+    sub_response.status_code = 200
+    sub_response.headers = {}
+    sub_response.text = json.dumps({
+        "$id": "/schemas/v1/sub.schema.json",
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "title": "Sub",
+        "type": "string",
+        "pattern": "^[0-9a-f]{8}$",
+    })
+    httpx_get_mock = mocker.patch("httpx.get", side_effect=[main_response, sub_response])
+    output_dir = tmp_path / "output"
+
+    result = run_main_with_args([
+        "--url",
+        "http://localhost:8888/schemas/v1/main.schema.json",
+        "--output",
+        str(output_dir),
+        "--input-file-type",
+        "jsonschema",
+        "--output-model-type",
+        "pydantic_v2.BaseModel",
+    ])
+
+    assert result == Exit.OK
+    main_content = (output_dir / "__init__.py").read_text(encoding="utf-8")
+    sub_content = (output_dir / "sub.py").read_text(encoding="utf-8")
+    assert "class Main(BaseModel):" in main_content
+    assert "sub: sub_1.Schema" in main_content
+    assert "class Schema(RootModel[constr(pattern=r'^[0-9a-f]{8}$')]):" in sub_content
+    httpx_get_mock.assert_has_calls([
+        call(
+            "http://localhost:8888/schemas/v1/main.schema.json",
+            headers=None,
+            verify=True,
+            follow_redirects=True,
+            params=None,
+            timeout=30.0,
+        ),
+        call(
+            "http://localhost:8888/schemas/v1/sub.schema.json",
+            headers=None,
+            verify=True,
+            follow_redirects=True,
+            params=None,
+            timeout=30.0,
+        ),
+    ])
+
+
 def test_main_remote_ref_emits_deprecation_warning(mocker: MockerFixture, tmp_path: Path) -> None:
     """Test that implicit remote $ref fetching emits a FutureWarning when flag is not set."""
     person_response = mocker.Mock()

tests/test_reference.py

@@ -213,6 +213,16 @@ def test_resolve_ref_with_root_id_differs_from_base_url() -> None:
     assert result == "https://example.com/common/types.json#"
 
 
+def test_resolve_ref_with_relative_root_id_and_base_url() -> None:
+    """Relative root $id should be resolved against the retrieval URL before $ref resolution."""
+    resolver = ModelResolver(base_url="http://localhost:8888/schemas/v1/main.schema.json")
+    resolver.set_root_id("/schemas/v1/main.schema.json")
+
+    result = resolver.resolve_ref("sub.schema.json")
+
+    assert result == "http://localhost:8888/schemas/v1/sub.schema.json#"
+
+
 @pytest.mark.parametrize(
     ("base_url", "ref", "expected"),
     [