fix(fns): resolve return annotations with from __future__ import annotations#1326
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fix(fns): resolve return annotations with from __future__ import annotations#1326CrepuscularIRIS wants to merge 1 commit into
from __future__ import annotations#1326CrepuscularIRIS wants to merge 1 commit into
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…otations` When PEP 563 (`from __future__ import annotations`) is active, all type annotations become strings. `PythonFunction.from_function()` was reading `sig.return_annotation` directly, which returned a string like "Recipe" instead of the actual class. This caused `@marvin.fn` decorated functions to return strings instead of typed objects. Use `typing.get_type_hints()` to resolve stringified annotations back to their actual types, with a fallback to the original behavior when resolution fails (e.g., unresolvable forward references). Fixes PrefectHQ#950
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- auto-pr.sh: Real submission pipeline (discover → fix → review → PR) - github-pr-state.json: 0.5h interval, lock file prevents concurrency - github-hunt: DISABLED in heartbeat-driver - First real PR submitted: PrefectHQ/marvin#1326 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Closing this PR — no maintainer activity in 2+ weeks. Happy to reopen or resubmit if you'd like to revisit. Thanks for the project! |
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Summary
Fixes #950
When
from __future__ import annotations(PEP 563) is active in a module, all type annotations become strings at runtime.PythonFunction.from_function()readssig.return_annotationdirectly, which returns a string like"Recipe"instead of the actualRecipeclass. This causes@marvin.fndecorated functions to produce string outputs instead of typed Pydantic model instances.Root Cause
inspect.signature(func).return_annotationreturns the raw annotation value. Under PEP 563, annotations are stored as strings and not evaluated until explicitly resolved. The fix atsrc/marvin/utilities/types.py:372was using this raw value without resolution.Changes
src/marvin/utilities/types.py: Add_resolve_return_annotation()helper that usestyping.get_type_hints()to resolve stringified annotations, with a fallback tosig.return_annotationwhen resolution fails (handles unresolvable forward refs, built-in functions, etc.)tests/basic/utilities/test_types.py: Add 4 tests covering: future annotations resolution, normal annotations, no annotation, and unresolvable forward ref fallbacktests/basic/utilities/_future_annotations_helper.py: Test helper module withfrom __future__ import annotationsactiveTesting
# Verify: uv run pytest tests/basic/utilities/test_types.py -vNotes
Minimal fix — only changes the annotation resolution path. No unrelated changes. The approach follows the same
typing.get_type_hints()strategy suggested in #1258. The exception handler is narrowed toKeyError | NameError | AttributeError | TypeErrorto avoid masking unexpected errors.