Fix parsing nested custom root type models

[Shados]

Change Summary

When validating fields that are pydantic models, if all else fails explicitly check if __custom_root_type__ is true, and try to parse_obj if it is.

Related issue number

Fixes #1190.

Checklist

• Unit tests for the changes exist
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes where applicable
• changes/<pull request or issue id>-<github username>.md file added describing change
  (see changes/README.md for details)

[codecov]

Codecov Report

Merging #1253 into master will decrease coverage by 0.10%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##            master    #1253      +/-   ##
===========================================
- Coverage   100.00%   99.89%   -0.11%     
===========================================
  Files           21       21              
  Lines         3666     3708      +42     
  Branches       718      731      +13     
===========================================
+ Hits          3666     3704      +38     
- Misses           0        2       +2     
- Partials         0        2       +2     

Impacted Files	Coverage Δ
pydantic/utils.py	98.92% <0.00%> (-1.08%)	⬇️
pydantic/schema.py	99.44% <0.00%> (-0.56%)	⬇️
pydantic/color.py	100.00% <0.00%> (ø)
pydantic/fields.py	100.00% <0.00%> (ø)
pydantic/typing.py	100.00% <0.00%> (ø)
pydantic/validators.py	100.00% <0.00%> (ø)

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[samuelcolvin]

looks like we still don't have a test for nested root models like i put on the issue.

Otherwise LGTM.

[Shados]

looks like we still don't have a test for nested root models like i put on the issue.

Otherwise LGTM.

Not sure which you mean. I do have the example parse_as_obj case included. I guess I could split that out into its own test?

[samuelcolvin]

There's still no explicit test for a custom root type as as the type of a custom root type:

from pydantic import BaseModel

class Foo(BaseModel):
    __root__: Dict[str, int]

class Bar(BaseModel):
    __root__: Foo

[Shados]

@samuelcolvin I have no idea why anyone would want do that explicitly, but I've added a test covering it.

[samuelcolvin]

thanks so much.