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Reject conflicting member layouts in multiple inheritance #9041

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Merged
youknowone merged 1 commit into from
Oct 10, 2026
Merged

Reject conflicting member layouts in multiple inheritance #9041

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6 changes: 5 additions & 1 deletion crates/vm/src/builtins/type.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3677,7 +3677,11 @@ fn mro_internal(typ: &Py<PyType>, vm: &VirtualMachine) -> PyResult<i32> {

/// Returns true if the two types have different instance layouts.
fn shape_differs(t1: &Py<PyType>, t2: &Py<PyType>) -> bool {
t1.slots.basicsize != t2.slots.basicsize || t1.slots.itemsize != t2.slots.itemsize
// Prefix member cells do not change basicsize, but still make a base
// solid: unrelated slotted bases cannot share the same member indexes.
t1.slots.basicsize != t2.slots.basicsize
|| t1.slots.itemsize != t2.slots.itemsize
|| t1.slots.member_count != t2.slots.member_count
}

fn solid_base<'a>(typ: &'a Py<PyType>, vm: &VirtualMachine) -> &'a Py<PyType> {
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50 changes: 50 additions & 0 deletions extra_tests/snippets/builtin_type.py
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Expand Up @@ -748,3 +748,53 @@ class StrKey(str):
warnings.simplefilter("error")
with assert_raises(RuntimeWarning):
type("NonStringKeyRaises", (), {6: 7})


class Left:
__slots__ = ("left",)


class Right:
__slots__ = ("right",)


with assert_raises(TypeError):

class Conflict(Left, Right):
pass
Comment on lines +761 to +764

@chatgpt-codex-connector chatgpt-codex-connector Bot Oct 10, 2026

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P1 Badge Remove the disallowed test-logic block

This appended scenario changes test logic and assertions in extra_tests/snippets/builtin_type.py, but the root AGENTS policy explicitly limits test-file modifications to adding or removing expected-failure decorators and related TODO comments. Remove this block or obtain an explicit policy exception before landing it.

AGENTS.md reference: AGENTS.md:L273-L279

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with assert_raises(TypeError):

class ReverseConflict(Right, Left):
pass


class Empty:
__slots__ = ()


class Compatible(Left, Empty):
pass


value = Compatible()
value.left = 42
assert value.left == 42


class FirstChild(Left):
__slots__ = ()


class SecondChild(Left):
__slots__ = ()


class Diamond(FirstChild, SecondChild):
pass


value = Diamond()
value.left = 43
assert value.left == 43
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