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Add support for converters with TypeVars on generic attrs classes#14908

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Merged
hauntsaninja merged 3 commits intopython:masterfromchadrik:attrs_converters
Mar 25, 2023
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42 changes: 39 additions & 3 deletionsmypy/plugins/attrs.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -6,8 +6,10 @@
from typing_extensions import Final, Literal

import mypy.plugin # To avoid circular imports.
from mypy.applytype import apply_generic_arguments
from mypy.checker import TypeChecker
from mypy.errorcodes import LITERAL_REQ
from mypy.expandtype import expand_type
from mypy.exprtotype import TypeTranslationError, expr_to_unanalyzed_type
from mypy.messages import format_type_bare
from mypy.nodes import (
Expand All@@ -23,6 +25,7 @@
Decorator,
Expression,
FuncDef,
IndexExpr,
JsonDict,
LambdaExpr,
ListExpr,
Expand All@@ -34,6 +37,7 @@
SymbolTableNode,
TempNode,
TupleExpr,
TypeApplication,
TypeInfo,
TypeVarExpr,
Var,
Expand All@@ -49,7 +53,7 @@
deserialize_and_fixup_type,
)
from mypy.server.trigger import make_wildcard_trigger
from mypy.typeops import make_simplified_union, map_type_from_supertype
from mypy.typeops importget_type_vars,make_simplified_union, map_type_from_supertype
from mypy.types import (
AnyType,
CallableType,
Expand DownExpand Up@@ -85,8 +89,9 @@
class Converter:
"""Holds information about a `converter=` argument"""

def __init__(self, init_type: Type | None = None) -> None:
def __init__(self, init_type: Type | None = None, ret_type: Type | None = None) -> None:
self.init_type = init_type
self.ret_type = ret_type


class Attribute:
Expand DownExpand Up@@ -115,11 +120,20 @@ def __init__(
def argument(self, ctx: mypy.plugin.ClassDefContext) -> Argument:
"""Return this attribute as an argument to __init__."""
assert self.init

init_type: Type | None = None
if self.converter:
if self.converter.init_type:
init_type = self.converter.init_type
if init_type and self.init_type and self.converter.ret_type:
# The converter return type should be the same type as the attribute type.
# Copy type vars from attr type to converter.
converter_vars = get_type_vars(self.converter.ret_type)
init_vars = get_type_vars(self.init_type)
if converter_vars and len(converter_vars) == len(init_vars):
variables = {
binder.id: arg for binder, arg in zip(converter_vars, init_vars)
}
init_type = expand_type(init_type, variables)
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@chadrikchadrikMar 16, 2023•
edited
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The idea behind this change is that a converter should ideally return the same type as the attrs field that it is added to. For example:

deflist_converter(x:Iterable[T])->List[T]:returnlist(x)@attr.s(auto_attribs=True)classA(Generic[T]):x:List[T]=attr.ib(converter=list_converter)

A.x is typeList[T] andlist_converter returnsList[T], and in theory this should always be the case for converters, since their purpose is to convert the init arg to the type of the field. In my changes I'm forgoing a complete comparison of the two types, but the assumption tells us that the number and order of TypeVars should be the same. We use that to generate a replacement map which will replace the converter's broken typevars, with typevars that work within the class's context.

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(I assume thedef int_gen slipped in from another example?)

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yep. I fixed the example.

else:
ctx.api.fail("Cannot determine __init__ type from converter", self.context)
init_type = AnyType(TypeOfAny.from_error)
Expand DownExpand Up@@ -653,6 +667,26 @@ def _parse_converter(
from mypy.checkmember import type_object_type # To avoid import cycle.

converter_type = type_object_type(converter_expr.node, ctx.api.named_type)
elif (
isinstance(converter_expr, IndexExpr)
and isinstance(converter_expr.analyzed, TypeApplication)
and isinstance(converter_expr.base, RefExpr)
and isinstance(converter_expr.base.node, TypeInfo)
):
# The converter is a generic type.
from mypy.checkmember import type_object_type # To avoid import cycle.

converter_type = type_object_type(converter_expr.base.node, ctx.api.named_type)
if isinstance(converter_type, CallableType):
converter_type = apply_generic_arguments(
converter_type,
converter_expr.analyzed.types,
ctx.api.msg.incompatible_typevar_value,
converter_type,
)
else:
converter_type = None

if isinstance(converter_expr, LambdaExpr):
# TODO: should we send a fail if converter_expr.min_args > 1?
converter_info.init_type = AnyType(TypeOfAny.unannotated)
Expand All@@ -671,6 +705,8 @@ def _parse_converter(
converter_type = get_proper_type(converter_type)
if isinstance(converter_type, CallableType) and converter_type.arg_types:
converter_info.init_type = converter_type.arg_types[0]
if not is_attr_converters_optional:
converter_info.ret_type = converter_type.ret_type
elif isinstance(converter_type, Overloaded):
types: list[Type] = []
for item in converter_type.items:
Expand Down
50 changes: 50 additions & 0 deletionstest-data/unit/check-attr.test
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Original file line numberDiff line numberDiff line change
Expand Up@@ -469,6 +469,56 @@ A([1], '2') # E: Cannot infer type argument 1 of "A"

[builtins fixtures/list.pyi]

[case testAttrsGenericWithConverter]
from typing import TypeVar, Generic, List, Iterable, Iterator, Callable
import attr
T = TypeVar('T')

def int_gen() -> Iterator[int]:
yield 1

def list_converter(x: Iterable[T]) -> List[T]:
return list(x)

@attr.s(auto_attribs=True)
class A(Generic[T]):
x: List[T] = attr.ib(converter=list_converter)
y: T = attr.ib()
def foo(self) -> List[T]:
return [self.y]
def bar(self) -> T:
return self.x[0]
def problem(self) -> T:
return self.x # E: Incompatible return value type (got "List[T]", expected "T")
reveal_type(A) # N: Revealed type is "def [T] (x: typing.Iterable[T`1], y: T`1) -> __main__.A[T`1]"
a1 = A([1], 2)
reveal_type(a1) # N: Revealed type is "__main__.A[builtins.int]"
reveal_type(a1.x) # N: Revealed type is "builtins.list[builtins.int]"
reveal_type(a1.y) # N: Revealed type is "builtins.int"

a2 = A(int_gen(), 2)
reveal_type(a2) # N: Revealed type is "__main__.A[builtins.int]"
reveal_type(a2.x) # N: Revealed type is "builtins.list[builtins.int]"
reveal_type(a2.y) # N: Revealed type is "builtins.int"


def get_int() -> int:
return 1

class Other(Generic[T]):
def __init__(self, x: T) -> None:
pass

@attr.s(auto_attribs=True)
class B(Generic[T]):
x: Other[Callable[..., T]] = attr.ib(converter=Other[Callable[..., T]])

b1 = B(get_int)
reveal_type(b1) # N: Revealed type is "__main__.B[builtins.int]"
reveal_type(b1.x) # N: Revealed type is "__main__.Other[def (*Any, **Any) -> builtins.int]"

[builtins fixtures/list.pyi]


[case testAttrsUntypedGenericInheritance]
from typing import Generic, TypeVar
Expand Down
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