Environment variables and complex fields in submodels

[mikepqr]

With this code

from typing import List, Union

from pydantic import BaseSettings


class D(BaseSettings):
    x: List[str] = ["foo", "bar"]


class C(BaseSettings):
    d: D = D()

    class Config:
        env_nested_delimiter = "__"


c = C()
print(C())
print(type(c.d.x))

this works fine

$ X='["baz"]' python -m t.py
d=D(x=['baz'])
<class 'list'>

but this fails (note environment variable):

$ D__X='["baz"]' python -m config_env_null
Traceback (most recent call last):
  File "/Users/mlw/.pyenv/versions/3.9.14/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/Users/mlw/.pyenv/versions/3.9.14/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/Users/mlw/tmp/pydantic/t.py", line 17, in <module>
    c = C()
  File "pydantic/env_settings.py", line 39, in pydantic.env_settings.BaseSettings.__init__
  File "pydantic/main.py", line 342, in pydantic.main.BaseModel.__init__
pydantic.error_wrappers.ValidationError: 1 validation error for C
d -> x
  value is not a valid list (type=type_error.list)

I asssume this is for the reason mentioned in the docs, i.e.

JSON is only parsed in top-level fields

That's fine. My question is about the solution suggested in the rest of the sentence, which is described extremely tersely:

if you need to parse JSON in sub-models, you will need to implement validators on those models.

This is my guess at what it means.

import json
from typing import Any, List, Union

from pydantic import BaseSettings, validator


class D(BaseSettings):
    x: Union[str, List[str]] = ["foo", "bar"]

    @validator("x")
    def _assemble_x(cls, x):
        if isinstance(x, str):
            return json.loads(x)
        else:
            return x


class C(BaseSettings):
    d: D = D()

    class Config:
        env_nested_delimiter = "__"


c = C()
print(C())
print(type(c.d.x))

$ D__X='["baz"]' python -m config_env_null
d=D(x=['baz'])
<class 'list'>

Is this what the docs are suggesting, or do they mean something else? (And would you take a PR to clarify this bit of the docs, or would you rather not encourage these kinds of hacks while gearing up for v2, etc.)