flag: DISALLOW_INSTANTIATION by youknowone · Pull Request #6445 · RustPython/RustPython

youknowone

Walkthrough

Replaces the Unconstructible trait with a new DISALLOW_INSTANTIATION PyTypeFlags across many pyclass declarations, removes the Unconstructible trait, refines pyclass derive slot/Constructor handling, and updates type initialization and new binding to propagate new-slot behavior.

Changes

Cohort / File(s)	Summary
Derive macro `crates/derive-impl/src/pyclass.rs`	Normalizes slot identifiers (case-insensitive), updates slot-name error message to allow const fn pointers, removes Constructor/Unconstructible enforcement path and related TODOs.
Core trait removal `crates/vm/src/types/slot.rs`	Removed the `Unconstructible` trait and its slot_new implementation that returned a type error.
Type system & class init `crates/vm/src/builtins/type.rs`, `crates/vm/src/class.rs`	`new_heap`/`new_static` now take `mut slots`; added `set_new` helper; adjusted HEAPTYPE/tp_new propagation. Class init binds `__new__` only when a type defines its own new slot (object is special-cased).
VM pyclasses: iterators, views, builtins `crates/vm/src/builtins/...` (asyncgenerator.rs, builtin_func.rs, bytearray.rs, bytes.rs, coroutine.rs, descriptor.rs, dict.rs, frame.rs, generator.rs, getset.rs, list.rs, memory.rs, range.rs, set.rs, str.rs, tuple.rs)	Replaced `with(..., Unconstructible, ...)` with `flags(DISALLOW_INSTANTIATION), with(...)`; removed `impl Unconstructible` blocks and Unconstructible imports where applicable.
Protocol & stdlib pyclasses `crates/vm/src/protocol/buffer.rs`, `crates/stdlib/src/...` (array.rs, csv.rs, pystruct.rs, sqlite.rs, unicodedata.rs, zlib.rs, ctypes/field.rs, os.rs)	Added `flags(DISALLOW_INSTANTIATION)` to many pyclass declarations (iterators, Reader/Writer, Blob/Statement, Ucd, Compress/Decompress, VecBuffer, PyCField, DirEntry, ScandirIterator, UnpackIterator); removed Unconstructible mixins/imports/impls.
Manifest `Cargo.toml`	(unchanged content summary present in diff metadata)

Sequence Diagram(s)

sequenceDiagram
    autonumber
    participant Derive as pyclass derive
    participant TypeSys as type creation (new_heap/new_static)
    participant ClassInit as class initialization (class.rs)
    note right of Derive: Macro resolves pyclass attrs\n(normalize slot names, detect Constructor)
    Derive->>TypeSys: emit PyTypeSlots (with/without new slot)
    TypeSys->>TypeSys: set_new(slots, base)  -- mutate slots,tp_new propagation
    TypeSys->>ClassInit: register slots on type
    ClassInit->>ClassInit: if own slot_new then bind __new__
    ClassInit-->>TypeSys: final type ready with DISALLOW_INSTANTIATION flag

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

Focus review areas:
- crates/derive-impl/src/pyclass.rs — slot name normalization and Constructor-related logic.
- crates/vm/src/builtins/type.rs — set_new, mutable slots handling, HEAPTYPE/tp_new timing.
- crates/vm/src/class.rs — conditional new binding correctness and object special-case.
- Search for any residual references to Unconstructible or assumptions about its slot_new behavior.
- Spot-check representative pyclass changes across VM and stdlib for consistent application.

Possibly related PRs

PyType::py_new to return Self #6398 — Modifies constructor/slot_new/py_new machinery; overlaps with type/slot initialization changes.
Pyfunction builtins and constructor #5823 — Adjusts Constructor usage in pyclass derive logic; related to derive macro recognition changes.
Use Unconstructible trait for internal types #6052 — Previously changed sqlite Blob/Statement constructibility; directly touches the same pyclasses updated here.

Suggested reviewers

ShaharNaveh

Poem

"🐰 I hopped through traits and flags today,
Unconstructible went on its way.
DISALLOW_INSTANTIATION plants a sign,
Slots propagated, and new aligned.
A nimble refactor — carrot cake time! 🥕"

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 60.19% which is insufficient. The required threshold is 80.00%.	You can run `@coderabbitai generate docstrings` to improve docstring coverage.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'flag: DISALLOW_INSTANTIATION' clearly and concisely summarizes the main change: introducing the DISALLOW_INSTANTIATION flag throughout the codebase.
Linked Issues check	✅ Passed	The pull request fully implements the objective from #5286 by adding DISALLOW_INSTANTIATION flag to prevent unintended instantiation of various types across the codebase.
Out of Scope Changes check	✅ Passed	All changes are directly related to the DISALLOW_INSTANTIATION implementation. The systematic replacement of Unconstructible trait with the DISALLOW_INSTANTIATION flag is within scope of the linked objective.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

✨ Finishing touches

📝 Generate docstrings

🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment

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