[explore] nested config with defaults

[jamiedemaria]

Summary & Motivation

from
https://dagsterlabs.slack.com/archives/C06QU0WBCQ5/p1734624150011189

It looks like if you set nested config with defaults, those dont get respected.

Example

 class NestedConfig(dg.Config):
     a: str
     b: int

 class AssetConfigSetDefaultsForNested(dg.Config):
     nested: NestedConfig = Field(default=NestedConfig(a="a", b=1))
     c: int = 1

@dg.asset
def example_with_asset_config_defaults(context, config: AssetConfigSetDefaultsForNested) -> None:
     context.log.info(f"nested.a: {config.nested.a}, nested.b: {config.nested.b}, c: {config.c}")

When you try to materialize the asset, you have to fill in values for nested in the launchpad

Making this PR with a test case demonstrating the behavior as a place to start documenting the behavior and investigating solutions since I likely won't be able to get a fix in before going on PTO.

One thought I had was that this might be considered an anti-pattern, but pydantic supports this

from pydantic import BaseModel


class Nested(BaseModel):
    a: str = "a"
    b: int


class Outer(BaseModel):
    foo: Nested = Nested(b=1)

print(Outer())
# foo=Nested(a='a', b=1)

How I Tested These Changes

Changelog

Insert changelog entry or delete this section.

[jamiedemaria]

• [explore] nested config with defaults #26603 👈 (View in Graphite)
• master

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[jamiedemaria]

My thought was that we'd pass the default values to infer_schema_from_config_class and then propogate those down the recursion until they reach the intended non-Config fields. We'd have to deal with overrides, but that seems simple enough - the default set at the higher level would override one set on a lower model.