Support for Union with ForwardRef

[Czaki]

for code:

Node = ForwardRef('Node')

class Node(BaseModel):
    left: Union[Node, Leaf]
    op: str
    right: Union[Node, Leaf]

there was warning /home/czaki/Projekty/PartSeg/docs/autodoc_pydantic.rst: WARNING: JSON schema can't be generated for 'PartSegCore.analysis.measurement_base.Node' because the following pydantic fields can't be serialized properly: ['left', 'right'].

in this code

autodoc_pydantic/sphinxcontrib/autodoc_pydantic/inspection.py

Lines 183 to 189 in 36ffae3

	try:
	field_args = (field.type_, field.default)
	model = create_model("_", test_field=field_args, Config=Cfg)
	model.schema()
	return True
	except Exception:
	return False

there is no check for sub_fields:
https://github.com/samuelcolvin/pydantic/blob/fbf8002cefd1ba7b263f63545fff2e48a378189d/pydantic/typing.py#L445-L458

in my case field.type_ is typing.Union[ForwardRef('Node'), PartSegCore.analysis.measurement_base.Leaf] but field.sub_fields is [ModelField(name="left_ForwardRef('Node')", type=Node, required=True), ModelField(name='left_Leaf', type=Leaf, required=True)]

So all data are available in data structures.

[mansenfranzen]

@Czaki Thanks for sharing this issue. It is definitely a bug. I can reproduce the behavior and it boils down to recursively check sub_fields as you have pointed it out. It will be fixed in the upcoming release.

[mansenfranzen]

@Czaki This should be fixed via #102.

Before merging the related PR, it would be great if you could test the bug fix on your site to confirm that my test case did indeed capture the incorrect behavior which you've encountered. To do so, please install the current dev release in your doc-building-environment via pip install git+https://github.com/mansenfranzen/[email protected] and rebuild your docs.

[mansenfranzen]

@all-contributors please add @Czaki for bug

[allcontributors]

@mansenfranzen

I've put up a pull request to add @Czaki! 🎉

[mansenfranzen]

@Czaki Please feel free to reopen this ticket if the issue persists.