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[ty] Implement Python's floor division semantics for Literal ints (#18249)

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Division works differently in Python than in Rust. If the result is
negative and there is a remainder, the division rounds down (instead of
towards zero). The remainder needs to be adjusted to compensate so that
`(lhs // rhs) * rhs + (lhs % rhs) == lhs`.

Fixes astral-sh/ty#481.
This commit is contained in:
Brandt Bucher 2025-05-22 10:42:29 -04:00 • committed by GitHub
parent 98da200d45
commit 91b7a570c2
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2 changed files with 50 additions and 10 deletions
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32
crates/ty_python_semantic/src/types/infer.rs
View file

@ -6108,17 +6108,29 @@ impl<'db> TypeInferenceBuilder<'db> {
Some(KnownClass::Float.to_instance(self.db()))
}
(Type::IntLiteral(n), Type::IntLiteral(m), ast::Operator::FloorDiv) => Some(
n.checked_div(m)
.map(Type::IntLiteral)
.unwrap_or_else(|| KnownClass::Int.to_instance(self.db())),
),
(Type::IntLiteral(n), Type::IntLiteral(m), ast::Operator::FloorDiv) => Some({
let mut q = n.checked_div(m);
let r = n.checked_rem(m);
// Division works differently in Python than in Rust. If the result is negative and
// there is a remainder, the division rounds down (instead of towards zero):
if n.is_negative() != m.is_negative() && r.unwrap_or(0) != 0 {
q = q.map(|q| q - 1);
}
q.map(Type::IntLiteral)
.unwrap_or_else(|| KnownClass::Int.to_instance(self.db()))
}),
(Type::IntLiteral(n), Type::IntLiteral(m), ast::Operator::Mod) => Some(
n.checked_rem(m)
.map(Type::IntLiteral)
.unwrap_or_else(|| KnownClass::Int.to_instance(self.db())),
),
(Type::IntLiteral(n), Type::IntLiteral(m), ast::Operator::Mod) => Some({
let mut r = n.checked_rem(m);
// Division works differently in Python than in Rust. If the result is negative and
// there is a remainder, the division rounds down (instead of towards zero). Adjust
// the remainder to compensate so that q * m + r == n:
if n.is_negative() != m.is_negative() && r.unwrap_or(0) != 0 {
r = r.map(|x| x + m);
}
r.map(Type::IntLiteral)
.unwrap_or_else(|| KnownClass::Int.to_instance(self.db()))
}),
(Type::IntLiteral(n), Type::IntLiteral(m), ast::Operator::Pow) => Some({
if m < 0 {