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Commit 8279fa6

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hauntsaninjahauntsaninja
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Conformance tests and spec change for generic type erasure (#1589)
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‎conformance/results/mypy/generics_type_erasure.toml

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conformant = "Partial"
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notes = """
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Infers Node[Never] instead of Node[Any] when argument is not provided.
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False negative on instance attribute access on type(node).
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"""
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output = """
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generics_type_erasure.py:17: error: Expression is of type "Node[Never]", not "Node[Any]" [assert-type]
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generics_type_erasure.py:20: error: Expression is of type Never, not "Any" [assert-type]
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generics_type_erasure.py:36: error: Argument 1 to "Node" has incompatible type "str"; expected "int | None" [arg-type]
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generics_type_erasure.py:38: error: Argument 1 to "Node" has incompatible type "int"; expected "str | None" [arg-type]
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generics_type_erasure.py:40: error: Access to generic instance variables via class is ambiguous [misc]
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generics_type_erasure.py:41: error: Access to generic instance variables via class is ambiguous [misc]
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generics_type_erasure.py:42: error: Access to generic instance variables via class is ambiguous [misc]
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generics_type_erasure.py:43: error: Access to generic instance variables via class is ambiguous [misc]
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"""

‎conformance/results/pyre/generics_type_erasure.toml

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conformant = "Partial"
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notes = """
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Doesn't allow using Node[Any] in assert_type expression.
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False negatives on instance attribute access on the type.
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"""
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output = """
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generics_type_erasure.py:11:0 Uninitialized attribute [13]: Attribute `label` is declared in class `Node` to have type `Variable[T]` but is never initialized.
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generics_type_erasure.py:17:25 Incompatible parameter type [6]: In call `typing.GenericMeta.__getitem__`, for 1st positional argument, expected `Type[Variable[T]]` but got `object`.
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generics_type_erasure.py:36:15 Incompatible parameter type [6]: In call `Node.__init__`, for 1st positional argument, expected `Optional[int]` but got `str`.
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generics_type_erasure.py:38:15 Incompatible parameter type [6]: In call `Node.__init__`, for 1st positional argument, expected `Optional[str]` but got `int`.
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"""

‎conformance/results/pyright/generics_type_erasure.toml

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conformant = "Partial"
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notes = """
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False negatives on instance attribute access on the type.
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"""
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output = """
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generics_type_erasure.py:36:16 - error: Argument of type "Literal['']" cannot be assigned to parameter "label" of type "int | None" in function "__init__"
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  Type "Literal['']" cannot be assigned to type "int | None"
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    "Literal['']" is incompatible with "int"
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    "Literal['']" is incompatible with "None" (reportGeneralTypeIssues)
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generics_type_erasure.py:38:16 - error: Argument of type "Literal[0]" cannot be assigned to parameter "label" of type "str | None" in function "__init__"
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  Type "Literal[0]" cannot be assigned to type "str | None"
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    "Literal[0]" is incompatible with "str"
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    "Literal[0]" is incompatible with "None" (reportGeneralTypeIssues)
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generics_type_erasure.py:42:6 - error: Cannot assign member "label" for type "type[Node[T@Node]]"
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  Expression of type "Literal[1]" cannot be assigned to member "label" of class "Node[T@Node]"
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    Member "__set__" is unknown
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    Type "Literal[1]" cannot be assigned to type "T@Node" (reportGeneralTypeIssues)
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"""

‎conformance/results/pytype/generics_type_erasure.toml

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conformant = "Unsupported"
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output = """
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NotImplementedError: ParameterizedClass
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"""

‎conformance/tests/generics_type_erasure.py

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# Specification: https://typing.readthedocs.io/en/latest/spec/generics.html#instantiating-generic-classes-and-type-erasure
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from typing import Any, TypeVar, Generic, assert_type
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T = TypeVar("T")
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# > If the constructor (__init__ or __new__) uses T in its signature, and a
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# > corresponding argument value is passed, the type of the corresponding
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# > argument(s) is substituted. Otherwise, Any is assumed.
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class Node(Generic[T]):
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label: T
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def __init__(self, label: T | None = None) -> None: ...
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assert_type(Node(''), Node[str])
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assert_type(Node(0), Node[int])
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assert_type(Node(), Node[Any])
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assert_type(Node(0).label, int)
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assert_type(Node().label, Any)
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# > In case the inferred type uses [Any] but the intended type is more specific,
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# > you can use an annotation to force the type of the variable, e.g.:
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n1: Node[int] = Node()
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assert_type(n1, Node[int])
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n2: Node[str] = Node()
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assert_type(n2, Node[str])
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n3 = Node[int]()
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assert_type(n3, Node[int])
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n4 = Node[str]()
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assert_type(n4, Node[str])
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n5 = Node[int](0) # OK
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n6 = Node[int]("") # Type error
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n7 = Node[str]("") # OK
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n8 = Node[str](0) # Type error
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Node[int].label = 1 # Type error
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Node[int].label # Type error
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Node.label = 1 # Type error
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Node.label # Type error
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type(n1).label # Type error
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assert_type(n1.label, int)
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assert_type(Node[int]().label, int)
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n1.label = 1 # OK
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# > [...] generic versions of concrete collections can be instantiated:
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from typing import DefaultDict
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data = DefaultDict[int, bytes]()
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assert_type(data[0], bytes)

‎docs/spec/generics.rst

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@@ -333,15 +333,15 @@ argument(s) is substituted. Otherwise, ``Any`` is assumed. Example::
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class Node(Generic[T]):
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x: T # Instance attribute (see below)
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def __init__(self, label: T = None) -> None:
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def __init__(self, label: T | None = None) -> None:
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...
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x = Node('') # Inferred type is Node[str]
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y = Node(0) # Inferred type is Node[int]
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z = Node() # Inferred type is Node[Any]
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In case the inferred type uses ``[Any]`` but the intended type is more
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specific, you can use a type comment (see below) to force the type of
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specific, you can use an annotation (see below) to force the type of
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the variable, e.g.::
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# (continued from previous example)
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Node.x = 1 # Error
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Node.x # Error
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type(p).x # Error
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p.x # Ok (evaluates to None)
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Node[int]().x # Ok (evaluates to None)
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p.x # Ok (evaluates to int)
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Node[int]().x # Ok (evaluates to int)
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p.x = 1 # Ok, but assigning to instance attribute
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Generic versions of abstract collections like ``Mapping`` or ``Sequence``

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