`F821` on use of `Literal` with strings, e.g. `Literal['foo']`

[samuelcolvin]

Since #119 was fixed via #125, I tried ruff again (build from main) with pydantic.

I get a few remaining F821 errors due to use of strings in Literal, the line numbers are also incorrect - seems to always be 1.

From this code (and some other places in that file), I get:

pydantic/config.py:1:1: F821 Undefined name `deep`
pydantic/config.py:1:1: F821 Undefined name `none`
pydantic/config.py:1:1: F821 Undefined name `deep`
pydantic/config.py:1:1: F821 Undefined name `shallow`
pydantic/config.py:1:1: F821 Undefined name `before_validation`
pydantic/config.py:1:1: F821 Undefined name `after_validation`
pydantic/config.py:1:1: F821 Undefined name `none`
pydantic/config.py:1:1: F821 Undefined name `shallow`
pydantic/config.py:1:1: F821 Undefined name `before_validation`
pydantic/config.py:1:1: F821 Undefined name `after_validation`

Example code:

    copy_on_model_validation: Literal['none', 'deep', 'shallow']
    post_init_call: Literal['before_validation', 'after_validation']

[samuelcolvin]

I have no idea how you differentiate in a general way between the following:

---

from typing import Literal

def foo(x: Literal['int']):
    pass

---

from typing import List

def foo(x: List['int']):
    pass

---

from .local_types import CustomThing

def foo(x: CustomThing['int']):
    pass

---

Obviously you can whitelist Literal, but I have no idea how you would work out whether CustomThing is parameterised with strings or types which might be strings.

I guess you have to assume it's parameterised with types, can maybe one day allow a magic comment or magic property which tells ruff that CustomThing is parameterised with literals - maybe there's a pep for this, but I don't know of it.

[charliermarsh]

Yeah it looks like PyFlakes special-cases Literal: https://github.com/PyCQA/pyflakes/blob/master/pyflakes/checker.py#L1464. Will fix.

PyFlakes actually has a lot of custom logic for caching forward-reference annotation in cast and TypeVar calls which we're yet to handle, so this may pop up there too.

[charliermarsh]

(The 1:1 issue will be handled separately, tracking in #132. Thank you!)

[vianmixtkz]

I still have the same issue

What version of ruff fixes it ?

I am using ruff==0.0.254

[charliermarsh]

@vianmixtkz - This was fixed long long ago. How are you importing Literal?

[vianmixtkz]

Gotcha,

I was importing it from another module. I tried to import it directly from typing and it fixed the issue.
Thanks.

What caused that though ?

[charliermarsh]

If you add that module to typing-modules, that should fix the issue for you without having to import from typing directly. We don't trace imports across files, so if you import Literal in one file, export it, and then import that export elsewhere, we don't know that it's equivalent to typing.Literal. By adding your first-party module to typing-modules, you can tell Ruff that anything imported from that module should be considered equivalent to a typing import.