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Reviewing files that changed from the base of the PR and between ee74713 and 63c3ba3.

• Lib/test/test_types.py is excluded by !Lib/**

• crates/derive-impl/src/pyclass.rs
• crates/vm/src/builtins/type.rs
• crates/vm/src/object/core.rs
• crates/vm/src/object/mod.rs

crates/derive-impl/src/pyclass.rs (1)

456-463: LGTM! Documentation clarifies basicsize computation.

The updated comment accurately reflects that when repr(transparent) with a base is not present, basicsize stores only the payload size, and the SIZEOF_PYOBJECT_HEAD is added separately in the __basicsize__ getter. This aligns with the implementation changes in crates/vm/src/builtins/type.rs.

crates/vm/src/object/mod.rs (1)

10-10: LGTM! Appropriate crate-internal re-export.

The pub(crate) visibility correctly limits access to within the VM crate while making SIZEOF_PYOBJECT_HEAD available for internal basicsize calculations.

crates/vm/src/object/core.rs (1)

117-117: LGTM! Clean calculation of object header size.

Using std::mem::size_of::<PyInner<()>>() is an elegant way to compute the PyObject header size by measuring the struct with a zero-sized type payload. The pub(crate) visibility is appropriate for internal use in basicsize calculations.

crates/vm/src/builtins/type.rs (5)

1341-1352: LGTM! Correct gating logic for dict addition.

The may_add_dict guard properly prevents adding a dict when the primary base class already has one (checking !base.slots.flags.has_feature(PyTypeFlags::HAS_DICT)). The updated condition on line 1350 correctly combines:

1. No __slots__ defined AND base doesn't have dict (automatic dict), OR
2. __dict__ explicitly in __slots__

This matches CPython's behavior of checking tp_dictoffset == 0 on the base.

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1354-1360: LGTM! Proper itemsize inheritance from base type.

Line 1358 correctly propagates itemsize from the base type during heap type creation. This is essential for correctly handling subclasses of variable-length types (e.g., tuple, list, bytes) where itemsize determines the per-element size.

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2019-2022: LGTM! Clean helper for layout comparison.

The shape_differs function encapsulates layout comparison logic, checking both __basicsize__() (instance size) and itemsize (per-element size for variable-length types). This improves code readability and maintainability.

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2024-2032: LGTM! Refactored to use shape_differs helper.

Line 2031 now uses the shape_differs helper for clearer intent. The logic remains equivalent: if the derived type has a different layout than its base, it becomes the solid base; otherwise, continue up the chain.

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785-787: Remove unnecessary concern about const removal—the change is correct and has no breaking callers.

The removal of const from __basicsize__ is correct. The only usage in the codebase (line 2021 in shape_differs) is a normal runtime call. The #[pygetset] decorator indicates this is a Python property getter, which cannot be const. No existing code depends on this being a const fn.