fix(types): don't treat instance methods on Enum output types as choices

[ErenAta16]

Fixes #1915.

_get_enum_members scans an Enum class's __dict__ for plain FunctionType values to support enums whose members are assigned as bare functions (e.g. c = some_function), since Python's Enum machinery treats a plain function assigned in the class body as a method rather than a member - it doesn't show up through normal iteration.

The scan had no way to tell that pattern apart from an actual instance method defined with def directly in the class body (e.g. describe(self)). Both end up as plain FunctionType objects in __dict__, so any Enum used as an output type that happened to also define a helper method crashed:

from enum import Enum
from outlines.types.dsl import python_types_to_terms

class Color(Enum):
    RED = "red"
    GREEN = "green"
    BLUE = "blue"

    def describe(self) -> str:
        return f"This color is {self.value}"

python_types_to_terms(Color)
# ValueError: Each argument must have a type annotation

describe gets swept up as a "member," and building a JSON schema from its signature fails on the unannotated self - a misleading error unrelated to the actual problem.

Fix

__qualname__ distinguishes the two cases: a method defined directly in the class body is qualified with the enclosing class's own name ("Color.describe"), while a function defined elsewhere and merely assigned as a member's value keeps its original qualname ("some_function"). Filtering on __qualname__ excludes real instance methods while still picking up the bare-function-member pattern that test_dsl_python_types_to_terms's SomeEnum.c = func case already covers.

I initially proposed restricting the scan to functools.partial values only (mentioned in the issue), but that turned out to be too narrow - it broke the existing SomeEnum.c = func test, which assigns a plain function directly without partial. Left a correction comment on the issue with the details; the __qualname__ approach here preserves that pattern.

Testing

Added test_dsl_enum_with_instance_method_is_not_a_choice to tests/types/test_dsl.py, covering the crash case from the issue.

Ran the full tests/types/ suite locally (233 tests, all passing), plus tests/types/test_dsl.py and tests/types/test_types_utils.py specifically to make sure the existing SomeEnum/enum-related coverage still passes unchanged.

[github-actions]

📚 Documentation preview: https://dottxt-ai.github.io/outlines/pr-preview/pr-1916/

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[RobinPicard]

Good catch, thanks!