Multiple issues when using `StrictUndefined` in app.jinja_env.undefined

[ddorian]

I like to use StrictUndefined to catch more errors in my templates. This raises many errors in flask-admin. You can simply check by enabling it in tests.

from jinja2 import StrictUndefined
app.jinja_env.undefined = StrictUndefined

Environment:

• Python version:3.12
• Flask version:3.0.3
• Flask-Admin version:2.0.0a0

For now I'm using a custom class to ignore these (I configure all flask-admin blueprints to start with admin2):

class MyStrictUndefined(StrictUndefined):
    """Work like StrictUndefined except in flask-admin views/blueprints."""

    @property
    def is_admin2_blp(self) -> bool:
        if flask.request and flask.request.blueprint:
            return bool(flask.request.blueprint.startswith("admin2"))
        return False

    def __eq__(self, other: t.Any) -> bool:  # type: ignore[override]
        if self.is_admin2_blp:
            return type(self) is type(other)
        self._fail_with_undefined_error()

    def __ne__(self, other: t.Any) -> bool:  # type: ignore[override]
        if self.is_admin2_blp:
            return not self.__eq__(other)
        self._fail_with_undefined_error()

    #
    # def __hash__(self) -> int:
    #    return id(type(self))
    #
    # def __str__(self) -> str:
    #    return ""
    #
    # def __len__(self) -> int:
    #    return 0
    #
    # def __iter__(self) -> t.Iterator[t.Any]:
    #    yield from ()
    #
    # async def __aiter__(self) -> t.AsyncIterator[t.Any]:
    #    for _ in ():
    #        yield

    def __bool__(self) -> bool:  # type: ignore[override]
        if self.is_admin2_blp:
            return False
        self._fail_with_undefined_error()

    # def __repr__(self) -> str:
    #    return "Undefined"

[samuelhwilliams]

Agree this would be nice to fix - would be very happy to accept a PR on this 🙏