Depending on email-validator>=2 is backwards incompatible

[marcuslimdw]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

Pydantic v1 has code to check whether the installed version of email-validator is 1 or 2 and act accordingly. On the other hand, Pydantic v2 only works with email-validator>=2, which is a backwards incompatible change that is not in the migration guide, which seems like a bug to me. IMO, there're two possible resolutions to this issue:

1. Add code to make Pydantic v2 able to handle email-validator<2 (and therefore drop the constraint in the optional dependency)
2. Change the docs to note that if you had email-validator<2 installed and upgraded to Pydantic 2, your code will break

This is not directly relevant, but I would really prefer 1, because currently I have Airflow, FastAPI, and Pydantic 2 installed in the same pyproject.toml. Airflow is preventing me from updating email-validator, and FastAPI's /docs endpoint is not displaying because it depends on Pydantic 2's EmailStr, which breaks with email-validator<2.

Example Code

No response

Python, Pydantic & OS Version

pydantic version: 2.5.1
        pydantic-core version: 2.14.3
          pydantic-core build: profile=release pgo=false
                 install path: <redacted>/venv/lib/python3.8/site-packages/pydantic
               python version: 3.8.16 (default, May 29 2023, 14:51:39)  [Clang 14.0.3 (clang-1403.0.22.14.1)]
                     platform: macOS-14.1.1-arm64-arm-64bit
             related packages: email-validator-1.3.1 typing_extensions-4.8.0 pyright-1.1.329 fastapi-0.104.1

[Viicos]

Version was bumped because of #3772.

Airflow is preventing me from updating email-validator

I'm not sure I understand, I don't see any dependency to email-validator in airflow?

Change the docs to note that if you had email-validator<2 installed and upgraded to Pydantic 2, your code will break

There's an open PR to add a version check (that could prevent breaking user code without them knowing it): #6033

[marcuslimdw]

@Viicos it's a transitive dependency; Airflow depends on Flask-AppBuilder, which depends on email-validator.

[Viicos]

Best would be to have Flask-AppBuilder loosen their dependencies. I see they put hard caps on almost every library which isn't really a good practice. But as it is not one of your direct dependencies it might be hard to have the change reflected on your environment even if a new release of Flask-AppBuilder gets out :/

[marcuslimdw]

@Viicos you're definitely right - not really looking for pydantic to change anything on the code side here, but IMO it would be really good to note this in the migration guide, above and beyond the PR you mentioned, because if the problematic code is only run in an obscure code path that is not tested, it may be hard to debug

[sydney-runkle]

Also related: #6033.

Can clean that up and work on getting that across the line today.