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red-knot: support narrowing for bool(E) #14668

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Dec 3, 2024
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Original file line number Diff line number Diff line change
@@ -0,0 +1,32 @@
## Narrowing for `bool(..)` checks

```py
def flag() -> bool: ...

x = 1 if flag() else None

# valid invocation, positive
reveal_type(x) # revealed: Literal[1] | None
if bool(x is not None):
reveal_type(x) # revealed: Literal[1]

# valid invocation, negative
reveal_type(x) # revealed: Literal[1] | None
if not bool(x is not None):
reveal_type(x) # revealed: None

# no args/narrowing
reveal_type(x) # revealed: Literal[1] | None
if not bool():
reveal_type(x) # revealed: Literal[1] | None

# invalid invocation, too many positional args
reveal_type(x) # revealed: Literal[1] | None
if bool(x is not None, 5): # TODO diagnostic
reveal_type(x) # revealed: Literal[1] | None

# invalid invocation, too many kwargs
reveal_type(x) # revealed: Literal[1] | None
if bool(x is not None, y=5): # TODO diagnostic
reveal_type(x) # revealed: Literal[1] | None
```
76 changes: 47 additions & 29 deletions crates/red_knot_python_semantic/src/types/narrow.rs
Original file line number Diff line number Diff line change
Expand Up @@ -385,42 +385,60 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
let scope = self.scope();
let inference = infer_expression_types(self.db, expression);

let callable_ty =
inference.expression_ty(expr_call.func.scoped_expression_id(self.db, scope));

// TODO: add support for PEP 604 union types on the right hand side of `isinstance`
// and `issubclass`, for example `isinstance(x, str | (int | float))`.
match inference
.expression_ty(expr_call.func.scoped_expression_id(self.db, scope))
.into_function_literal()
.and_then(|f| f.known(self.db))
.and_then(KnownFunction::constraint_function)
{
Some(function) if expr_call.arguments.keywords.is_empty() => {
if let [ast::Expr::Name(ast::ExprName { id, .. }), class_info] =
match callable_ty {
Type::FunctionLiteral(function_type) if expr_call.arguments.keywords.is_empty() => {
let function = function_type
.known(self.db)
.and_then(KnownFunction::constraint_function)?;

let [ast::Expr::Name(ast::ExprName { id, .. }), class_info] =
&*expr_call.arguments.args
{
let symbol = self.symbols().symbol_id_by_name(id).unwrap();
else {
return None;
};

let class_info_ty =
inference.expression_ty(class_info.scoped_expression_id(self.db, scope));
let symbol = self.symbols().symbol_id_by_name(id).unwrap();

let to_constraint = match function {
KnownConstraintFunction::IsInstance => {
|class_literal: ClassLiteralType<'db>| {
Type::instance(class_literal.class)
}
}
KnownConstraintFunction::IsSubclass => {
|class_literal: ClassLiteralType<'db>| {
Type::subclass_of(class_literal.class)
}
let class_info_ty =
inference.expression_ty(class_info.scoped_expression_id(self.db, scope));

let to_constraint = match function {
KnownConstraintFunction::IsInstance => {
|class_literal: ClassLiteralType<'db>| Type::instance(class_literal.class)
}
KnownConstraintFunction::IsSubclass => {
|class_literal: ClassLiteralType<'db>| {
Type::subclass_of(class_literal.class)
}
};
}
};

generate_classinfo_constraint(self.db, &class_info_ty, to_constraint).map(
|constraint| {
let mut constraints = NarrowingConstraints::default();
constraints.insert(symbol, constraint.negate_if(self.db, !is_positive));
constraints
},
)
}
Type::ClassLiteral(..) => {
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let is_valid_bool_invocation =
expr_call.arguments.args.len() == 1 && expr_call.arguments.keywords.is_empty();

generate_classinfo_constraint(self.db, &class_info_ty, to_constraint).map(
|constraint| {
let mut constraints = NarrowingConstraints::default();
constraints.insert(symbol, constraint.negate_if(self.db, !is_positive));
constraints
},
if is_valid_bool_invocation
&& callable_ty
.into_class_literal()
.is_some_and(|lit| lit.class.is_known(self.db, KnownClass::Bool))
{
self.evaluate_expression_node_constraint(
&expr_call.arguments.args[0],
expression,
is_positive,
)
} else {
None
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