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[dataclass_transform] minimal implementation of dataclass_transform #14523

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wesleywright
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This is a very simple first step to implementing PEP 0681, which will allow MyPy to recognize user-defined types that behave similarly to dataclasses.

This initial implementation is very limited: we only support decorator-style use of typing.dataclass_transform and do not support passing additional options to the transform (such as freeze or init).

Within MyPy, we add a new is_dataclass_transform field to FuncBase which is populated during semantic analysis. When we check for plugin hooks later, we add new special cases to use the existing dataclasses plugin if a class decorator is marked with is_dataclass_transform. Ideally we would use a proper plugin API; the hacky special case here can be replaced in subsequent iterations.

… dataclasses plugin

This is a very simple first step to implementing [PEP
0681](https://peps.python.org/pep-0681/#decorator-function-example),
which will allow MyPy to recognize user-defined types that behave
similarly to dataclasses.

This initial implementation is very limited: we only support
decorator-style use of `typing.dataclass_transform` and do not support
passing additional options to the transform (such as `freeze` or
`init`).

Within MyPy, we add a new `is_dataclass_transform` field to
`FuncBase` which is populated during semantic analysis. When we check
for plugin hooks later, we add new special cases to use the dataclasses
plugin if a class decorator is marked with `is_dataclass_transform`.
Ideally we would use a proper plugin API; the hacky special case here
can be replaced in subsequent iterations.
@@ -19,7 +19,7 @@
Var,
)
from mypy.plugin import CheckerPluginInterface, ClassDefContext, SemanticAnalyzerPluginInterface
from mypy.semanal import ALLOW_INCOMPATIBLE_OVERRIDE, set_callable_name
from mypy.semanal_shared import ALLOW_INCOMPATIBLE_OVERRIDE, set_callable_name
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this move was needed to avoid a cyclic dependency between semanal.py and plugins/common.py

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tmke8 commented Jan 25, 2023

I see only typing.dataclass_transform in the code; does this also work with typing_extensions.dataclass_transform?

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@wesleywright
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I see only typing.dataclass_transform in the code; does this also work with typing_extensions.dataclass_transform?

I think this is a gap currently, thanks for the catch (this is my first PR adding this kind of feature haha)

Comment on lines +40 to +44
class list(Generic[_T], Sequence[_T]):
def __contains__(self, item: object) -> int: pass
def __getitem__(self, key: int) -> _T: pass
def __iter__(self) -> Iterator[_T]: pass

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needed to use dataclasses.pyi and typing-full.pyi at the same time in a test case

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Thanks for the PR! This is solid basic implementation. You'll need to fix flake8, otherwise everything looks good.

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According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

@hauntsaninja hauntsaninja mentioned this pull request Jan 26, 2023
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Thanks, this looks great. Let's get this into 1.0. It's not complete, but it will result in strictly fewer errors for users of PEP 681 than current master.

@hauntsaninja hauntsaninja merged commit bac9e77 into python:master Jan 26, 2023
hauntsaninja pushed a commit to hauntsaninja/mypy that referenced this pull request Jan 26, 2023
…ython#14523)

This is a very simple first step to implementing [PEP
0681](https://peps.python.org/pep-0681/#decorator-function-example),
which will allow MyPy to recognize user-defined types that behave
similarly to dataclasses.

This initial implementation is very limited: we only support
decorator-style use of `typing.dataclass_transform` and do not support
passing additional options to the transform (such as `freeze` or
`init`).

Within MyPy, we add a new `is_dataclass_transform` field to `FuncBase`
which is populated during semantic analysis. When we check for plugin
hooks later, we add new special cases to use the existing dataclasses
plugin if a class decorator is marked with `is_dataclass_transform`.
Ideally we would use a proper plugin API; the hacky special case here
can be replaced in subsequent iterations.

Co-authored-by: Wesley Wright <wesleyw@dropbox.com>
hauntsaninja added a commit that referenced this pull request Jan 29, 2023
…#14532)

This is a very simple first step to implementing [PEP
0681](https://peps.python.org/pep-0681/#decorator-function-example),
which will allow MyPy to recognize user-defined types that behave
similarly to dataclasses.

This initial implementation is very limited: we only support
decorator-style use of `typing.dataclass_transform` and do not support
passing additional options to the transform (such as `freeze` or
`init`).

Within MyPy, we add a new `is_dataclass_transform` field to `FuncBase`
which is populated during semantic analysis. When we check for plugin
hooks later, we add new special cases to use the existing dataclasses
plugin if a class decorator is marked with `is_dataclass_transform`.
Ideally we would use a proper plugin API; the hacky special case here
can be replaced in subsequent iterations.

Co-authored-by: Wesley Collin Wright <deinlebenandern@gmail.com>
Co-authored-by: Wesley Wright <wesleyw@dropbox.com>
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5 participants