Introduce slot wrapper to init by youknowone · Pull Request #4884 · RustPython/RustPython

youknowone

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📝 Walkthrough

Walkthrough

Adds wrapper descriptor types (PySlotWrapper and PyMethodWrapper), exposes them in the type zoo, wires an init slot wrapper into class extension, hides the Initializer::slot_init Python binding, refines init return errors, and adds a no-op Initializer for PyWeak; also adjusts BufferedMixin init exposure.

Changes

Cohort / File(s)	Summary
Descriptor types `crates/vm/src/builtins/descriptor.rs`	Add `PySlotWrapper` and `PyMethodWrapper` pypayloads/pyclasses with descriptor semantics, binding (get), call delegation, represent, hash, and compare implementations; public accessors and reduce for method-wrapper.
Type registration `crates/vm/src/types/zoo.rs`	Add `wrapper_descriptor_type` and `method_wrapper_type` fields and initialize them via `PySlotWrapper::init_builtin_type()` and `PyMethodWrapper::init_builtin_type()`.
Class extension `crates/vm/src/class.rs`	Import `descriptor::PySlotWrapper` and instantiate/assign a `PySlotWrapper` as `__init__` on classes that define an init slot but lack an `__init__` in their dict.
Initializer/slot plumbing `crates/vm/src/types/slot.rs`	Remove `#[pymethod(name = "__init__")]` from `Initializer::slot_init` (no automatic Python binding) and change the init-wrapper error message to include the concrete return type name.
Base object init validation `crates/vm/src/builtins/object.rs`	Change `slot_init` parameter names to `(zelf, args, vm)` and add excess-args validation that considers heap vs non-heap types and whether `__new__`/`__init__` are overridden.
WeakRef initializer `crates/vm/src/builtins/weakref.rs`	Add `Initializer` impl (no-op) for `PyWeak`, include `Initializer` and `PyRef` in imports, and add `Initializer` to the pyclass trait list.
IO BufferedMixin cleanup `crates/vm/src/stdlib/io.rs`	Remove public `__init__` from `BufferedMixin` and call `init` directly in `slot_init` instead of delegating through `__init__`.

Sequence Diagram(s)

sequenceDiagram
    participant User as User Code
    participant Class as Class Object
    participant SW as PySlotWrapper
    participant MW as PyMethodWrapper
    participant Impl as Underlying Slot Impl

    User->>Class: access __init__
    Class->>SW: class-level descriptor lookup (PySlotWrapper)
    SW->>MW: __get__(instance) -> return PyMethodWrapper bound to instance
    User->>MW: call bound method ()
    MW->>SW: delegate call (enforce type, unwrap, forward)
    SW->>Impl: invoke underlying slot function (Init/New)
    Impl-->>User: result / return

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~50 minutes

Possibly related PRs

Introduce slot wrapper to __init__ #4884 — introduces PySlotWrapper/PyMethodWrapper and related descriptor/init-slot wiring (highly related).
init debug helper #6315 — changes to Initializer::slot_init handling and error messaging (closely related).
disallow __new__, __init__ #6446 — overlaps on initializer/slot exposure and wiring between Initializer and slot_init.

Suggested reviewers

arihant2math
ShaharNaveh
coolreader18

Poem

🐰 I wrap the slots, I bind with care,
A method friend appears to share.
Init checks tighten, errors shine bright,
Small hops of code, all snug tonight. 🥕

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 48.28% which is insufficient. The required threshold is 80.00%.	You can run `@coderabbitai generate docstrings` to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Introduce slot wrapper to init' directly describes the main change—adding PySlotWrapper and PyMethodWrapper descriptor support, with PySlotWrapper specifically wrapping the init slot. The title is concise and accurately reflects the primary objective of the changeset.

📜 Recent review details

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 3cb6b52 and 1f9df15.

⛔ Files ignored due to path filters (4)

Lib/test/test_descr.py is excluded by !Lib/**
Lib/test/test_inspect/test_inspect.py is excluded by !Lib/**
Lib/test/test_types.py is excluded by !Lib/**
Lib/test/test_weakref.py is excluded by !Lib/**

📒 Files selected for processing (7)

crates/vm/src/builtins/descriptor.rs
crates/vm/src/builtins/object.rs
crates/vm/src/builtins/weakref.rs
crates/vm/src/class.rs
crates/vm/src/stdlib/io.rs
crates/vm/src/types/slot.rs
crates/vm/src/types/zoo.rs

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Introduce slot wrapper to __init__ by youknowone · Pull Request #4884 · RustPython/RustPython