feat(vm/slot): implement `Py_TPFLAGS_MANAGED_DICT` for class objects #5949

ever0de · 2025-07-11T15:41:51Z

Reference

~~Waiting for CPython Issue(PR)~~
~~python/cpython#136535~~

#5949 (comment)

Summary by CodeRabbit

New Features
- Improved handling of type attributes for custom classes, ensuring correct support for types with and without __slots__.
Bug Fixes
- Fixed an issue where types with __slots__ were incorrectly assigned dictionary-related flags.
Chores
- Updated internal flags to better represent type characteristics.

coderabbitai · 2025-07-11T15:42:02Z

Walkthrough

The changes introduce a new MANAGED_DICT flag to the type flags system and update type construction logic to conditionally set the HAS_DICT and MANAGED_DICT flags only when the __slots__ attribute is absent. This refines the way the runtime tracks dictionary management capabilities of Python types.

Changes

File(s)	Change Summary
vm/src/builtins/type.rs	Adjusted type construction: `HAS_DICT` and new `MANAGED_DICT` flags set only if `__slots__` absent. Removed old TODO comment.
vm/src/types/slot.rs	Added `MANAGED_DICT` constant to `PyTypeFlags` bitflags struct.

Poem

In the warren of types, a new flag appears,
For managed dicts, the intent now clears.
If slots are defined, no dicts to be found,
But without them, both flags abound!
With bits set just right, the VM hops on,
Type logic refined, and the bugs are all gone.
🐇✨

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Lib/test/test_array.py is excluded by !Lib/**
Lib/test/test_importlib/test_metadata_api.py is excluded by !Lib/**
Lib/test/test_property.py is excluded by !Lib/**
Lib/test/test_weakref.py is excluded by !Lib/**

📒 Files selected for processing (2)

vm/src/builtins/type.rs (1 hunks)
vm/src/types/slot.rs (1 hunks)

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**/*.rs

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🔇 Additional comments (2)

vm/src/types/slot.rs (1)

125-125: LGTM - Correct implementation of MANAGED_DICT flag.

The new MANAGED_DICT flag is properly implemented following the existing pattern. The bit position (1 << 4 = 16) is appropriate and doesn't conflict with existing flags.

vm/src/builtins/type.rs (1)

1072-1077: LGTM - Correct conditional flag setting logic.

The implementation properly conditionalizes the HAS_DICT and MANAGED_DICT flags based on the presence of __slots__. This aligns with CPython's behavior where types defining __slots__ don't use managed dictionaries for attribute storage. The logic is clear and well-commented.

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youknowone · 2025-07-20T01:37:08Z

vm/src/builtins/type.rs

+        let mut flags = PyTypeFlags::heap_type_flags();
+        // Only add HAS_DICT and MANAGED_DICT if __slots__ is not defined.
+        if heaptype_slots.is_none() {
+            flags |= PyTypeFlags::HAS_DICT | PyTypeFlags::MANAGED_DICT;
+        }
+


How about splitting the patch one to contains this part and the other one contains the test_class part? I'd like to merge the test_class part as the same form of CPython patch, but this one doesn't need to be.

I'll split the test_class part into a new PR.

ever0de · 2025-07-20T04:28:04Z

This implementation targets test_flags in test_class, but the test should be enabled only after the corresponding CPython PR is merged.

youknowone

Thank you!

ever0de force-pushed the feat/type-managed-dict-flag branch from b6f4667 to be42c2b Compare July 11, 2025 16:18

youknowone reviewed Jul 20, 2025

View reviewed changes

feat(vm/slot): implement Py_TPFLAGS_MANAGED_DICT for class objects

550fb30

ever0de force-pushed the feat/type-managed-dict-flag branch 2 times, most recently from a0cef6d to 6427732 Compare July 20, 2025 04:17

rollback test_class

32b24c1

ever0de force-pushed the feat/type-managed-dict-flag branch from 6427732 to 32b24c1 Compare July 20, 2025 04:26

ever0de marked this pull request as ready for review July 20, 2025 04:28

youknowone approved these changes Jul 20, 2025

View reviewed changes

youknowone merged commit ff35dcd into RustPython:main Jul 20, 2025
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feat(vm/slot): implement `Py_TPFLAGS_MANAGED_DICT` for class objects #5949

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