stubgen: emit synthesized __init__ for dataclass / Pydantic models#3306
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Pydantic models default to lax init parameter types and extra **kwargs, which made .pyi stubs noisy and unlike the source annotations. Stub extraction now reuses the checker's synthesized __init__, overlays class-body annotation text on matching parameters (including validation aliases), omits **kwargs from the stub, and forces alias-only init parameters to be keyword-only. Exposes ClassField::dataclass_flags_of to stubgen and treats re-exported BaseModel as a Pydantic model for metadata. Alternative to trimming field()/Field() on the class body (facebook#3223). Co-authored-by: Cursor <cursoragent@cursor.com>
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Context
As in #3221 / #3223, stub output for dataclass and Pydantic models needs to reflect how instances are constructed (defaults,
kw_only, validation aliases, etc.) without turning.pyifiles into a dump offield()/Field()kwargs.Intent
Alternative to #3223. Rather than primarily re-emitting a reduced
field()/Field()on the class line, this approach injects a synthesized__init__derived from the checker’s existing dataclass / Pydantic init plumbing, then aligns annotations with the authored class body where parameter names match (including alias-only init).Changes
extract.rs: Resolve synthesized__init__fromClassSynthesizedFields, mapParam→StubParam, merge AST annotation text for init params (skippingInitVar), drop**kwargsfrom emitted synthetic inits, preserve / improve class-body ordering andfield/Fieldelision behavior, import pruning for unused Pydantic helpers.emit.rs: Multilinedef __init__when the stub has many parameters.dataclass.rs: Validation-alias-only init parameters are keyword-only (*, id: ...), matching runtime and stub tests.pydantic.rs/class_field.rs: Treatpydantic.BaseModelre-exports like other BaseModel bases; exposeClassField::dataclass_flags_ofto stubgen.mod.rstests: Minimal on-diskpydanticshim + glob onlyinput.pyso temp package imports do not overwrite stubgen output.Testing
cargo test -p pyrefly stubgen::tests::Made with Cursor