Adds experimental_field decorator

[desertaxle]

Add an experimental_field decorator for use with Pydantic models. The decorator allows the user to define a field to warn on and will raise a warning if the correct conditions are met when the model is instantiated. I also wanted to allow the warning to raise whenever the specified value is set, but I didn't find a way to get that working.

Example

from pydantic import BaseModel
from prefect._internal.compatibility.experimental import experimental_field

@experimental_field(
    "value",
    group="test",
    help="This is just a test, don't worry.",
)
class Foo(BaseModel):
    value: int

Foo(value=1) # raises experimental warning

Checklist

• This pull request references any related issue by including "closes <link to issue>"
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• This pull request includes tests or only affects documentation.
• This pull request includes a label categorizing the change e.g. fix, feature, enhancement

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[zanieb]

Can this be implemented as this instead?

Suggested change

	@experimental_field(
	"value",
	group="test",
	help="This is just a test, don't worry.",
	)
	class Foo(BaseModel):
	value: int = 1
	class Foo(BaseModel):
	value: int = ExperimentalField(default=1, group="test", help="...")

It'd then add a validator to the field or something that raises the warning? It seems clearer perhaps?

[zanieb]

Or perhaps

Suggested change

	@experimental_field(
	"value",
	group="test",
	help="This is just a test, don't worry.",
	)
	class Foo(BaseModel):
	value: int = 1
	class Foo(BaseModel):
	value: int = ExperimentalField(Field(default=1, ...), group="test", help="...")

[desertaxle]

I tried that initially, but I couldn't find a way to add validator by wrapping Field. The validators for fields seem to be place on the class that is used as the type hint. Do you have an example of extending Field?

[zanieb]

Ah interesting. Let's stick with this for now then.

[desertaxle]

It looks like dynamically adding validators to an existing model isn't supported: pydantic/pydantic#2076

[peytonrunyan]

lgtm!