[ty] Use field-specifier return type as the default type for the field #20915
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sharkdp
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dcreager
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sharkdp
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Oct 16, 2025
| tag: str | None = field(default=None, init=False) | ||
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| # revealed: (self: Member, name: str, role: str = Literal["user"]) -> None | ||
| # revealed: (self: Member, name: str, role: str = str) -> None |
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This happens due to literal promotion, I guess.
sharkdp
commented
Oct 16, 2025
| timestamp: datetime = field(default_factory=datetime.now, init=False) | ||
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| # revealed: (self: Data, content: list[int] = list[Unknown]) -> None | ||
| # revealed: (self: Data, content: list[int] = list[int]) -> None |
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This shows that our previous approach, calling default_factory manually, was apparently too naive.
Diagnostic diff on typing conformance testsNo changes detected when running ty on typing conformance tests ✅ |
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AlexWaygood
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Oct 16, 2025
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Oct 16, 2025
…rable * origin/main: Don't use codspeed or depot runners in CI jobs on forks (#20894) [ty] cache Type::is_redundant_with (#20477) Fix run-away for mutually referential instance attributes (#20645) [ty] Limit shown import paths to at most 5 unless ty runs with `-v` (#20912) [ty] Use field-specifier return type as the default type for the field (#20915) [ty] Do not assume that `field`s have a default value (#20914) [ty] Fix match pattern value narrowing to use equality semantics (#20882) Update setup instructions for Zed 0.208.0+ (#20902) Move TOML indent size config (#20905) [syntax-errors]: implement F702 as semantic syntax error (#20869) [ty] Heterogeneous unpacking support for unions (#20377) [ty] refactor `Place` (#20871) Auto-accept snapshot changes as part of typeshed-sync PRs (#20892) [`airflow`] Add warning to `airflow.datasets.DatasetEvent` usage (`AIR301`) (#20551) [`flake8-pyi`] Fix operator precedence by adding parentheses when needed (`PYI061`) (#20508) [`pyupgrade`] Fix false negative for `TypeVar` with default argument in `non-pep695-generic-class` (`UP046`) (#20660) Update parser snapshots (#20893) Fix syntax error false positives for escapes and quotes in f-strings (#20867)
dcreager
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Oct 16, 2025
…nt-sets * dcreager/non-non-inferable: Don't use codspeed or depot runners in CI jobs on forks (#20894) [ty] cache Type::is_redundant_with (#20477) Fix run-away for mutually referential instance attributes (#20645) [ty] Limit shown import paths to at most 5 unless ty runs with `-v` (#20912) [ty] Use field-specifier return type as the default type for the field (#20915) [ty] Do not assume that `field`s have a default value (#20914) [ty] Fix match pattern value narrowing to use equality semantics (#20882) Update setup instructions for Zed 0.208.0+ (#20902) Move TOML indent size config (#20905) [syntax-errors]: implement F702 as semantic syntax error (#20869) [ty] Heterogeneous unpacking support for unions (#20377) [ty] refactor `Place` (#20871) Auto-accept snapshot changes as part of typeshed-sync PRs (#20892) [`airflow`] Add warning to `airflow.datasets.DatasetEvent` usage (`AIR301`) (#20551) [`flake8-pyi`] Fix operator precedence by adding parentheses when needed (`PYI061`) (#20508) [`pyupgrade`] Fix false negative for `TypeVar` with default argument in `non-pep695-generic-class` (`UP046`) (#20660) Update parser snapshots (#20893) Fix syntax error false positives for escapes and quotes in f-strings (#20867)
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Summary
dataclasses.fieldand field-specifier functions of commonly used libraries likepydantic,attrs, andSQLAlchemyall return the default type for the field (orAny) instead of an actualFieldinstance, even if this is not what happens at runtime. Let's make use of this fact and assume that all field specifiers return the type of the default value of the field.For standard dataclasses, this leads to more or less the same outcome (see test diff for details), but this change is important for 3rd party dataclass-transformers.
Test Plan
Tested the consequences of this change on the field-specifiers branch as well.