Type alias type by youknowone · Pull Request #6011 · RustPython/RustPython

youknowone

Walkthrough

The changes introduce stricter argument validation to the object.__new__ method in the object builtin, aligning its behavior with CPython. Additionally, a formal constructor with argument validation is implemented for TypeAliasType in the typing module, and the representation logic is unified using the Representable trait. The NodeAst type in the AST module gains a custom constructor implementing the Constructor trait with a specialized slot_new method.

Changes

File(s)	Change Summary
vm/src/builtins/object.rs	Enhanced `py_new` for `PyBaseObject` to validate arguments and match CPython's `object.__new__` logic.
vm/src/stdlib/typing.rs	Added `Constructor` impl for `TypeAliasType` with argument validation; unified `Representable` logic; updated `#[pyclass]` attributes and trait signatures.
vm/src/stdlib/ast/python.rs	Implemented `Constructor` trait for `NodeAst` with custom `slot_new` for controlled instance creation; updated `#[pyclass]` attribute.

Sequence Diagram(s)

sequenceDiagram
    participant Caller
    participant VM
    participant PyBaseObject
    participant PyType

    Caller->>VM: Call object.__new__(type, *args, **kwargs)
    VM->>PyType: Check __new__ and __init__ methods
    alt Arguments passed
        alt Custom __new__ or __init__
            VM->>PyBaseObject: Allow construction
        else Base __new__ and __init__
            VM->>Caller: Raise TypeError
        end
    else No arguments
        VM->>PyBaseObject: Proceed with construction
    end

sequenceDiagram
    participant Caller
    participant VM
    participant TypeAliasType

    Caller->>VM: Call TypeAliasType.__new__(cls, name, value, type_params=...)
    VM->>TypeAliasType: Validate argument count and types
    alt Argument validation fails
        VM->>Caller: Raise TypeError
    else Validation passes
        VM->>TypeAliasType: Create instance
        TypeAliasType-->>Caller: Return instance
    end

sequenceDiagram
    participant Caller
    participant VM
    participant NodeAst
    participant BaseObject

    Caller->>VM: Call NodeAst.__new__(cls, *args, **kwargs)
    VM->>NodeAst: slot_new creates base object with dict if needed
    NodeAst->>NodeAst: Call __init__ with args
    NodeAst-->>Caller: Return initialized instance

Estimated code review effort

vm/src/builtins/object.rs: 3 (120 minutes)
vm/src/stdlib/typing.rs: 3 (120 minutes)
vm/src/stdlib/ast/python.rs: 2 (60 minutes)

Suggested reviewers

arihant2math

Poem

In the warren of types, a new rule appears,
Constructors now check, and raise errors or cheers.
With arguments counted and types held tight,
The object’s creation is now just right.
Typing’s alias, too, stands proud and tall—
A hop, a skip, a bug-free call! 🐇

📜 Recent review details

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Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 2c7692b and 09c340a.

⛔ Files ignored due to path filters (3)

Lib/test/test_ast/test_ast.py is excluded by !Lib/**
Lib/test/test_collections.py is excluded by !Lib/**
Lib/test/test_exception_group.py is excluded by !Lib/**

📒 Files selected for processing (1)

vm/src/stdlib/ast/python.rs (2 hunks)

🧰 Additional context used

📓 Path-based instructions (1)

**/*.rs

Instructions used from:

Sources:
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.github/copilot-instructions.md

🧠 Learnings (2)

📓 Common learnings

Learnt from: youknowone
PR: RustPython/RustPython#5945
File: vm/src/stdlib/typing.rs:132-136
Timestamp: 2025-07-11T07:16:06.225Z
Learning: In Python 3.12, TypeAliasType's __repr__ method returns just the alias name as a string (e.g., repr(A) returns 'A'), not the "<TypeAliasType AliasName>" format. This applies to type aliases created with the `type` statement syntax.

vm/src/stdlib/ast/python.rs (1)

Learnt from: CR
PR: RustPython/RustPython#0
File: .github/copilot-instructions.md:0-0
Timestamp: 2025-07-19T03:16:56.511Z
Learning: Applies to **/*.rs : Use the macro system (pyclass, pymodule, pyfunction, etc.) when implementing Python functionality in Rust

🔇 Additional comments (3)

vm/src/stdlib/ast/python.rs (3)

7-7: LGTM! Import changes are well-organized.

The additional imports are necessary for the Constructor implementation and follow Rust conventions.

Also applies to: 9-9

16-16: LGTM! Pyclass attribute correctly enables Constructor trait.

The with(Constructor) addition properly enables the custom constructor implementation while preserving existing flags.

56-82: LGTM! Well-implemented Constructor trait following established patterns.

The implementation correctly:

Uses slot_new for fast object creation with proper dictionary allocation

Delegates initialization to the existing __init__ method

Handles the HAS_DICT flag appropriately for conditional dictionary creation

Follows the pattern established elsewhere in the codebase for standardizing constructor behavior

The comment explaining AST node behavior differences from object.__new__ is helpful for understanding the design choice.

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