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[ty] Consider __len__ when determining the truthiness of an instance of a tuple class or a @final class (#21049)

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This commit is contained in:
Alex Waygood
2025-10-24 10:29:55 +01:00
committed by GitHub
parent 4522f35ea7
commit e196c2ab37
6 changed files with 349 additions and 65 deletions
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52
crates/ty_python_semantic/resources/mdtest/expression/boolean.md
View File

@@ -78,7 +78,7 @@ python-version = "3.11"
```
```py
from typing import Literal
from typing import Literal, final
reveal_type(bool(1)) # revealed: Literal[True]
reveal_type(bool((0,))) # revealed: Literal[True]
@@ -92,15 +92,11 @@ reveal_type(bool(foo)) # revealed: Literal[True]
class SingleElementTupleSubclass(tuple[int]): ...
reveal_type(bool(SingleElementTupleSubclass((0,)))) # revealed: Literal[True]
reveal_type(SingleElementTupleSubclass.__bool__) # revealed: (self: tuple[int], /) -> Literal[True]
reveal_type(SingleElementTupleSubclass((1,)).__bool__) # revealed: () -> Literal[True]
# Unknown length, but we know the length is guaranteed to be >=2
class MixedTupleSubclass(tuple[int, *tuple[str, ...], bytes]): ...
reveal_type(bool(MixedTupleSubclass((1, b"foo")))) # revealed: Literal[True]
reveal_type(MixedTupleSubclass.__bool__) # revealed: (self: tuple[int, *tuple[str, ...], bytes], /) -> Literal[True]
reveal_type(MixedTupleSubclass((1, b"foo")).__bool__) # revealed: () -> Literal[True]
# Unknown length with an overridden `__bool__`:
class VariadicTupleSubclassWithDunderBoolOverride(tuple[int, ...]):
@@ -108,10 +104,6 @@ class VariadicTupleSubclassWithDunderBoolOverride(tuple[int, ...]):
return True
reveal_type(bool(VariadicTupleSubclassWithDunderBoolOverride((1,)))) # revealed: Literal[True]
reveal_type(VariadicTupleSubclassWithDunderBoolOverride.__bool__) # revealed: def __bool__(self) -> Literal[True]
# revealed: bound method VariadicTupleSubclassWithDunderBoolOverride.__bool__() -> Literal[True]
reveal_type(VariadicTupleSubclassWithDunderBoolOverride().__bool__)
# Same again but for a subclass of a fixed-length tuple:
class EmptyTupleSubclassWithDunderBoolOverride(tuple[()]):
@@ -124,11 +116,28 @@ reveal_type(EmptyTupleSubclassWithDunderBoolOverride.__bool__) # revealed: def
# revealed: bound method EmptyTupleSubclassWithDunderBoolOverride.__bool__() -> Literal[True]
reveal_type(EmptyTupleSubclassWithDunderBoolOverride().__bool__)
@final
class FinalClassOverridingLenAndNotBool:
def __len__(self) -> Literal[42]:
return 42
reveal_type(bool(FinalClassOverridingLenAndNotBool())) # revealed: Literal[True]
@final
class FinalClassWithNoLenOrBool: ...
reveal_type(bool(FinalClassWithNoLenOrBool())) # revealed: Literal[True]
def f(x: SingleElementTupleSubclass | FinalClassOverridingLenAndNotBool | FinalClassWithNoLenOrBool):
reveal_type(bool(x)) # revealed: Literal[True]
```
## Falsy values
```py
from typing import final, Literal
reveal_type(bool(0)) # revealed: Literal[False]
reveal_type(bool(())) # revealed: Literal[False]
reveal_type(bool(None)) # revealed: Literal[False]
@@ -139,13 +148,23 @@ reveal_type(bool()) # revealed: Literal[False]
class EmptyTupleSubclass(tuple[()]): ...
reveal_type(bool(EmptyTupleSubclass())) # revealed: Literal[False]
reveal_type(EmptyTupleSubclass.__bool__) # revealed: (self: tuple[()], /) -> Literal[False]
reveal_type(EmptyTupleSubclass().__bool__) # revealed: () -> Literal[False]
@final
class FinalClassOverridingLenAndNotBool:
def __len__(self) -> Literal[0]:
return 0
reveal_type(bool(FinalClassOverridingLenAndNotBool())) # revealed: Literal[False]
def f(x: EmptyTupleSubclass | FinalClassOverridingLenAndNotBool):
reveal_type(bool(x)) # revealed: Literal[False]
```
## Ambiguous values
```py
from typing import Literal
reveal_type(bool([])) # revealed: bool
reveal_type(bool({})) # revealed: bool
reveal_type(bool(set())) # revealed: bool
@@ -154,8 +173,15 @@ class VariadicTupleSubclass(tuple[int, ...]): ...
def f(x: tuple[int, ...], y: VariadicTupleSubclass):
reveal_type(bool(x)) # revealed: bool
reveal_type(x.__bool__) # revealed: () -> bool
reveal_type(y.__bool__) # revealed: () -> bool
class NonFinalOverridingLenAndNotBool:
def __len__(self) -> Literal[42]:
return 42
# We cannot consider `__len__` for a non-`@final` type,
# because a subclass might override `__bool__`,
# and `__bool__` takes precedence over `__len__`
reveal_type(bool(NonFinalOverridingLenAndNotBool())) # revealed: bool
```
## `__bool__` returning `NoReturn`

11
crates/ty_python_semantic/resources/mdtest/narrow/boolean.md
View File

@@ -21,6 +21,8 @@ def _(flag: bool):
## Narrowing in `and`
```py
from typing import final
def _(flag: bool):
class A: ...
x: A | None = A() if flag else None
@@ -28,6 +30,15 @@ def _(flag: bool):
isinstance(x, A) and reveal_type(x) # revealed: A
x is None and reveal_type(x) # revealed: None
reveal_type(x) # revealed: A | None
@final
class FinalClass: ...
# We know that no subclass of `FinalClass` can exist,
# therefore no subtype of `FinalClass` can define `__bool__`
# or `__len__`, therefore `FinalClass` can safely be considered
# always-truthy, therefore this always resolves to `None`
reveal_type(FinalClass() and None) # revealed: None
```
## Multiple `and` arms

70
crates/ty_python_semantic/src/types.rs
View File

@@ -4463,18 +4463,15 @@ impl<'db> Type<'db> {
visitor: &TryBoolVisitor<'db>,
) -> Result<Truthiness, BoolError<'db>> {
let type_to_truthiness = |ty| {
if let Type::BooleanLiteral(bool_val) = ty {
Truthiness::from(bool_val)
} else {
Truthiness::Ambiguous
match ty {
Type::BooleanLiteral(bool_val) => Truthiness::from(bool_val),
Type::IntLiteral(int_val) => Truthiness::from(int_val != 0),
// anything else is handled lower down
_ => Truthiness::Ambiguous,
}
};
let try_dunder_bool = || {
// We only check the `__bool__` method for truth testing, even though at
// runtime there is a fallback to `__len__`, since `__bool__` takes precedence
// and a subclass could add a `__bool__` method.
let try_dunders = || {
match self.try_call_dunder(
db,
"__bool__",
@@ -4509,18 +4506,67 @@ impl<'db> Type<'db> {
Ok(Truthiness::Ambiguous)
}
Err(CallDunderError::MethodNotAvailable) => Ok(Truthiness::Ambiguous),
Err(CallDunderError::MethodNotAvailable) => {
// We only consider `__len__` for tuples and `@final` types,
// since `__bool__` takes precedence
// and a subclass could add a `__bool__` method.
//
// TODO: with regards to tuple types, we intend to emit a diagnostic
// if a tuple subclass defines a `__bool__` method with a return type
// that is inconsistent with the tuple's length. Otherwise, the special
// handling for tuples here isn't sound.
if let Some(instance) = self.into_nominal_instance() {
if let Some(tuple_spec) = instance.tuple_spec(db) {
Ok(tuple_spec.truthiness())
} else if instance.class(db).is_final(db) {
match self.try_call_dunder(
db,
"__len__",
CallArguments::none(),
TypeContext::default(),
) {
Ok(outcome) => {
let return_type = outcome.return_type(db);
if return_type.is_assignable_to(
db,
KnownClass::SupportsIndex.to_instance(db),
) {
Ok(type_to_truthiness(return_type))
} else {
// TODO: should report a diagnostic similar to if return type of `__bool__`
// is not assignable to `bool`
Ok(Truthiness::Ambiguous)
}
}
// if a `@final` type does not define `__bool__` or `__len__`, it is always truthy
Err(CallDunderError::MethodNotAvailable) => {
Ok(Truthiness::AlwaysTrue)
}
// TODO: errors during a `__len__` call (if `__len__` exists) should be reported
// as diagnostics similar to errors during a `__bool__` call (when `__bool__` exists)
Err(_) => Ok(Truthiness::Ambiguous),
}
} else {
Ok(Truthiness::Ambiguous)
}
} else {
Ok(Truthiness::Ambiguous)
}
}
Err(CallDunderError::CallError(CallErrorKind::BindingError, bindings)) => {
Err(BoolError::IncorrectArguments {
truthiness: type_to_truthiness(bindings.return_type(db)),
not_boolable_type: *self,
})
}
Err(CallDunderError::CallError(CallErrorKind::NotCallable, _)) => {
Err(BoolError::NotCallable {
not_boolable_type: *self,
})
}
Err(CallDunderError::CallError(CallErrorKind::PossiblyNotCallable, _)) => {
Err(BoolError::Other {
not_boolable_type: *self,
@@ -4635,9 +4681,9 @@ impl<'db> Type<'db> {
.known_class(db)
.and_then(KnownClass::bool)
.map(Ok)
.unwrap_or_else(try_dunder_bool)?,
.unwrap_or_else(try_dunders)?,
Type::ProtocolInstance(_) => try_dunder_bool()?,
Type::ProtocolInstance(_) => try_dunders()?,
Type::Union(union) => try_union(*union)?,

25
crates/ty_python_semantic/src/types/class.rs
View File

@@ -745,17 +745,6 @@ impl<'db> ClassType<'db> {
})
};
let synthesize_simple_tuple_method = |return_type| {
let parameters =
Parameters::new([Parameter::positional_only(Some(Name::new_static("self")))
.with_annotated_type(Type::instance(db, self))]);
let synthesized_dunder_method =
CallableType::function_like(db, Signature::new(parameters, Some(return_type)));
Member::definitely_declared(synthesized_dunder_method)
};
match name {
"__len__" if class_literal.is_tuple(db) => {
let return_type = specialization
@@ -765,16 +754,14 @@ impl<'db> ClassType<'db> {
.map(Type::IntLiteral)
.unwrap_or_else(|| KnownClass::Int.to_instance(db));
synthesize_simple_tuple_method(return_type)
}
let parameters =
Parameters::new([Parameter::positional_only(Some(Name::new_static("self")))
.with_annotated_type(Type::instance(db, self))]);
"__bool__" if class_literal.is_tuple(db) => {
let return_type = specialization
.and_then(|spec| spec.tuple(db))
.map(|tuple| tuple.truthiness().into_type(db))
.unwrap_or_else(|| KnownClass::Bool.to_instance(db));
let synthesized_dunder_method =
CallableType::function_like(db, Signature::new(parameters, Some(return_type)));
synthesize_simple_tuple_method(return_type)
Member::definitely_declared(synthesized_dunder_method)
}
"__getitem__" if class_literal.is_tuple(db) => {

27
crates/ty_python_semantic/src/types/ide_support.rs
View File

@@ -10,6 +10,7 @@ use crate::semantic_index::scope::ScopeId;
use crate::semantic_index::{
attribute_scopes, global_scope, place_table, semantic_index, use_def_map,
};
use crate::types::CallDunderError;
use crate::types::call::{CallArguments, MatchedArgument};
use crate::types::signatures::Signature;
use crate::types::{
@@ -973,13 +974,33 @@ pub fn definitions_for_unary_op<'db>(
ast::UnaryOp::Not => "__bool__",
};
let Ok(bindings) = operand_ty.try_call_dunder(
let bindings = match operand_ty.try_call_dunder(
db,
unary_dunder_method,
CallArguments::none(),
TypeContext::default(),
) else {
return None;
) {
Ok(bindings) => bindings,
Err(CallDunderError::MethodNotAvailable) if unary_op.op == ast::UnaryOp::Not => {
// The runtime falls back to `__len__` for `not` if `__bool__` is not defined.
match operand_ty.try_call_dunder(
db,
"__len__",
CallArguments::none(),
TypeContext::default(),
) {
Ok(bindings) => bindings,
Err(CallDunderError::MethodNotAvailable) => return None,
Err(
CallDunderError::PossiblyUnbound(bindings)
| CallDunderError::CallError(_, bindings),
) => *bindings,
}
}
Err(CallDunderError::MethodNotAvailable) => return None,
Err(
CallDunderError::PossiblyUnbound(bindings) | CallDunderError::CallError(_, bindings),
) => *bindings,
};
let callable_type = promote_literals_for_self(db, bindings.callable_type());