Implement Optional required

[tiangolo]

Change Summary

Make ModelField(required=True) keep the required flag.

This allows solving fastapi/fastapi#646 without hacks, and solves #990, allowing required nullables with:

class Model(BaseModel):
    nullable: Optional[int] = Field(...)

A benefit is that external libraries using Pydantic like FastAPI or others (and more to come) can create a ModelField object, set the required argument (ModelField(required=True)) and expect it to be preserved without having to re-set it after creation with field.required = True.

Related issue number

#990 #1028

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 #1031 into master will decrease coverage by 0.03%.
The diff coverage is 95.23%.

@@            Coverage Diff             @@
##           master    #1031      +/-   ##
==========================================
- Coverage     100%   99.96%   -0.04%     
==========================================
  Files          20       20              
  Lines        3316     3332      +16     
  Branches      653      659       +6     
==========================================
+ Hits         3316     3331      +15     
- Misses          0        1       +1

Impacted Files	Coverage Δ
pydantic/fields.py	99.71% <95.23%> (-0.29%)	⬇️

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[tiangolo]

This is ready for review @samuelcolvin , @dmontagu .

I didn't think the optional nullable was worth extra docs, but let me know if you think this should include some.

[samuelcolvin]

otherwise looking good.

[tiangolo]

Thanks for the code review! Done ✔️

[samuelcolvin]

Looks good, except on reflection we do need to update the docs.

We should extend this section to explain about required optional fields.

We should also add a note to this section pointing to the details on required optional fields.

[tiangolo]

Sure! 📝 Done ✔️

[dmontagu]

The mypy plugin may need to be changed to reflect this (either it needs to be, or it was a bug before 😅) I’ll take a look. Either way it won’t be hard.

[tiangolo]

Thanks @dmontagu !

I haven't been able to check out the mypy plug-in (although I look forward to using it) 😅

Should we do the update here or in a separate PR?

[dmontagu]

I looked at the mypy plugin code and it actually currently treats Optional[X] = ... as required 😄. So nothing to change there.

It would be nice to add tests for this, and I wrote some, but after some reflection I think it will be easiest to just put it in a separate PR (really need to make it easier to write unit tests for the mypy plugin...).

I'll take responsibility for writing additional mypy plugin tests, and I'll wait until after this is merged though and we make the desired behavior explicit.

---

I think it would be nice to add some tests here for Any too as noted above, just to make sure the logic is formalized somewhere. But that's the only thing left; if you or @samuelcolvin disagree about including those tests here, I'm good with this PR as is.

(Currently the plugin does not treat Any as non-required, so I guess as of v1.1 that's a bug that needs to be addressed; I'll fix that in the PR where I add the tests described above.)

[tiangolo]

Thanks for the review @dmontagu !

I added tests for Any as you suggested. Including explicit tests for a: Any vs b: Any = None.

I guess that will have to be updated if the current behavior is changed.

Thanks for taking care of the mypy plug-in! 💪 😎 🚀

[tiangolo]

Thanks for the review, I applied all the requested changes.

[samuelcolvin]

thanks so much, I'll release v1.2 now.

[tiangolo]

Thanks for fixing the tests I missed 🤦‍♂️

And thanks for merging this! 🎉 🚀