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[ty] Fall back to object for attribute access on synthesized protocols (#20286)

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Alex Waygood 2025-09-08 13:04:37 +01:00 • committed by GitHub
parent 982a0a2a7c
commit deb3d3d150
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4 changed files with 39 additions and 2 deletions
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8
crates/ty_python_semantic/resources/mdtest/annotations/callable.md
View file

@ -392,8 +392,14 @@ from inspect import getattr_static
def f_okay(c: Callable[[], None]):
if hasattr(c, "__qualname__"):
c.__qualname__ # okay
reveal_type(c.__qualname__) # revealed: object
# TODO: should be `property`
# (or complain that we don't know that `type(c)` has the attribute at all!)
reveal_type(type(c).__qualname__) # revealed: @Todo(Intersection meta-type)
# `hasattr` only guarantees that an attribute is readable.
#
# error: [invalid-assignment] "Object of type `Literal["my_callable"]` is not assignable to attribute `__qualname__` on type `(() -> None) & <Protocol with members '__qualname__'>`"
c.__qualname__ = "my_callable"

14
crates/ty_python_semantic/resources/mdtest/narrow/hasattr.md
View file

@ -84,3 +84,17 @@ def _(obj: MaybeWithSpam):
# error: [possibly-unbound-attribute]
reveal_type(obj.spam) # revealed: int
```
All attribute available on `object` are still available on these synthesized protocols, but
attributes that are not present on `object` are not available:
```py
def f(x: object):
if hasattr(x, "__qualname__"):
reveal_type(x.__repr__) # revealed: bound method object.__repr__() -> str
reveal_type(x.__str__) # revealed: bound method object.__str__() -> str
reveal_type(x.__dict__) # revealed: dict[str, Any]
# error: [unresolved-attribute] "Type `<Protocol with members '__qualname__'>` has no attribute `foo`"
reveal_type(x.foo) # revealed: Unknown
```

17
crates/ty_python_semantic/src/types.rs
View file

@ -3409,6 +3409,23 @@ impl<'db> Type<'db> {
Type::ModuleLiteral(module) => module.static_member(db, name_str),
// If a protocol does not include a member and the policy disables falling back to
// `object`, we return `Place::Unbound` here. This short-circuits attribute lookup
// before we find the "fallback to attribute access on `object`" logic later on
// (otherwise we would infer that all synthesized protocols have `__getattribute__`
// methods, and therefore that all synthesized protocols have all possible attributes.)
//
// Note that we could do this for *all* protocols, but it's only *necessary* for synthesized
// ones, and the standard logic is *probably* more performant for class-based protocols?
Type::ProtocolInstance(ProtocolInstanceType {
inner: Protocol::Synthesized(protocol),
..
}) if policy.mro_no_object_fallback()
&& !protocol.interface().includes_member(db, name_str) =>
{
Place::Unbound.into()
}
_ if policy.no_instance_fallback() => self.invoke_descriptor_protocol(
db,
name_str,

2
crates/ty_python_semantic/src/types/protocol_class.rs
View file

@ -227,7 +227,7 @@ impl<'db> ProtocolInterface<'db> {
place: Place::bound(member.ty()),
qualifiers: member.qualifiers(),
})
.unwrap_or_else(|| Type::object(db).instance_member(db, name))
.unwrap_or_else(|| Type::object(db).member(db, name))
}
/// Return `true` if if all members on `self` are also members of `other`.