Support PEP 604 unions (int | str) as output types

[sohumt123]

What this PR does

Fixes python_types_to_terms rejecting PEP 604 unions as output types. Passing int | str, str | None, or a nested form like list[int | str] currently raises:

TypeError: Type int | str is currently not supported. Please open an issue: https://github.com/dottxt-ai/outlines/issues

while the semantically identical typing.Union[int, str] / Optional[str] work fine.

Root cause

is_union in src/outlines/types/utils.py only checks get_origin(value) is typing.Union. For a PEP 604 union, get_origin(int | str) returns types.UnionType instead, so is_union returns False and python_types_to_terms (src/outlines/types/dsl.py) falls through every handler into the generic unsupported-type error.

Fix

Make is_union also accept types.UnionType instances:

def is_union(value: Any) -> bool:
    return get_origin(value) is Union or isinstance(value, types.UnionType)

No version guard is needed: pyproject.toml requires Python >=3.10 and types.UnionType exists since 3.10. get_args already treats both union forms identically, so _handle_union needs no changes — PEP 604 unions now produce terms string-identical to their typing.Union/Optional equivalents.

Tests

• tests/types/test_types_utils.py::test_is_union: added is_union(int | str) and is_union(str | None) assertions.
• tests/types/test_dsl.py::test_dsl_python_types_to_terms: added assertions that int | str, str | None, and list[int | str] dispatch identically to Union[int, str], Optional[str], and list[Union[int, str]].

Both tests fail on main without the one-line fix and pass with it. Full pytest tests/types/ passes: 232 passed.

[github-actions]

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[RobinPicard]

Good addition, thanks for opening a PR!