Pydantic doesn't properly parses models with custom root into custom root models

[gou177]

Initial Checks

• I have searched GitHub for a duplicate issue and I'm sure this is something new
• I have searched Google & StackOverflow for a solution and couldn't find anything
• I have read and followed the docs and still think this is a bug
• I am confident that the issue is with pydantic (not my code, or another library in the ecosystem like FastAPI or mypy)

Description

This is because _enforce_dict_if_root() checks only for dicts with root key but not for models with root key.

Example Code

from pydantic import BaseModel

class Test(BaseModel):
    __root__: int

Test.parse_obj(dict(Test.parse_obj(1))) # works fine

Test.parse_obj(Test.parse_obj(1))

# Expected: Test(__root__=1)

# Actual: pydantic.error_wrappers.ValidationError: 1 validation error for Test
# __root__
#   value is not a valid integer (type=type_error.integer)

Python, Pydantic & OS Version

pydantic version: 1.10.2
            pydantic compiled: True
                 install path: C:\Users\gou17\AppData\Local\Programs\Python\Python310\Lib\site-packages\pydantic
               python version: 3.10.4 (tags/v3.10.4:9d38120, Mar 23 2022, 23:13:41) [MSC v.1929 64 bit (AMD64)]
                     platform: Windows-10-10.0.22621-SP0
     optional deps. installed: ['dotenv', 'email-validator', 'typing-extensions']

Affected Components

• Compatibility between releases
• Data validation/parsing
• Data serialization - .dict() and .json()
• JSON Schema
• Dataclasses
• Model Config
• Field Types - adding or changing a particular data type
• Function validation decorator
• Generic Models
• Other Model behaviour - construct(), pickling, private attributes, ORM mode
• Plugins and integration with other tools - mypy, FastAPI, python-devtools, Hypothesis, VS Code, PyCharm, etc.

[samuelcolvin]

We're getting rid of custom root types in V2, and I doubt this can be changed in v1.10 now as I doubt it's a new bug.

Sorry.

[samuelcolvin]

Changed my mind, see #4884.