[red-knot] Class literal `new` function callable subtyping #17533

MatthewMckee4 · 2025-04-21T23:21:44Z

Summary

From https://typing.python.org/en/latest/spec/constructors.html#converting-a-constructor-to-callable

this covers step 2 and partially step 3 (always respecting the __new__)

Test Plan

Update is_subtype_of.md

github-actions · 2025-04-21T23:23:48Z

`mypy_primer` results

No ecosystem changes detected ✅

carljm

Looks good, thank you! Just a couple comments.

crates/red_knot_python_semantic/src/types.rs

crates/red_knot_python_semantic/resources/mdtest/type_properties/is_subtype_of.md

Co-authored-by: Carl Meyer <carl@oddbird.net>

crates/red_knot_python_semantic/resources/mdtest/type_properties/is_subtype_of.md

crates/red_knot_python_semantic/src/types.rs

playground/shared/package-lock.json

dhruvmanila

Thank you.

I think it would be useful to create a into_callable method on ClassLiteralType to avoid expanding the is_subtype_of and to keep the match arms simple.

dhruvmanila · 2025-04-22T15:57:50Z

crates/red_knot_python_semantic/src/types.rs

+                    let new_function = new_function.into_bound_method_type(db, self);
+                    return new_function.is_subtype_of(db, target);


nit:

Suggested change

let new_function = new_function.into_bound_method_type(db, self);

return new_function.is_subtype_of(db, target);

return new_function.into_bound_method_type(db, self).is_subtype_of(db, target);

dhruvmanila · 2025-04-22T16:00:14Z

crates/red_knot_python_semantic/src/types.rs

+    pub(crate) fn into_bound_method_type(
+        self,
+        db: &'db dyn Db,
+        self_instance: Type<'db>,


The parameter name is a bit misleading because in this PR above where this is being called it's not an instance of the class but the class itself. This is also the case for the field name on BoundMethodType which is also called self_instance. I'm not sure what to name it, maybe self_or_cls (and remove the _instance suffix).

Regardless, this shouldn't block this PR and something that could be done in a follow-up instead.

MatthewMckee4 · 2025-04-22T16:12:17Z

Sounds good

MatthewMckee4 · 2025-04-22T18:02:58Z

crates/red_knot_python_semantic/src/types/class.rs

+        let self_ty = Type::from(self);
+        let metaclass_call_function_symbol = self_ty
+            .member_lookup_with_policy(
+                db,
+                "__call__".into(),
+                MemberLookupPolicy::NO_INSTANCE_FALLBACK
+                    | MemberLookupPolicy::META_CLASS_NO_TYPE_FALLBACK,
+            )
+            .symbol;


For some reason this wasnt working

let metaclass_call_function_symbol = self .class_member( db, "__call__", MemberLookupPolicy::NO_INSTANCE_FALLBACK | MemberLookupPolicy::META_CLASS_NO_TYPE_FALLBACK, ) .symbol;

It couldn't find __call__

I suspect it found it, but it wasn't a BoundMethod. That's because it's Type::member_lookup_with_policy that implements the descriptor protocol, which turns a FunctionType into a BoundMethod.

carljm

Looks good, thank you!

carljm · 2025-04-23T05:39:56Z

crates/red_knot_python_semantic/src/types/class.rs

+        let self_ty = Type::from(self);
+        let metaclass_call_function_symbol = self_ty
+            .member_lookup_with_policy(
+                db,
+                "__call__".into(),
+                MemberLookupPolicy::NO_INSTANCE_FALLBACK
+                    | MemberLookupPolicy::META_CLASS_NO_TYPE_FALLBACK,
+            )
+            .symbol;


I suspect it found it, but it wasn't a BoundMethod. That's because it's Type::member_lookup_with_policy that implements the descriptor protocol, which turns a FunctionType into a BoundMethod.

* main: (28 commits) [red-knot] Make `BoundMethodType` a salsa interned (#17581) [red-knot] Emit a diagnostic if a non-protocol is passed to `get_protocol_members` (#17551) [red-knot] Add more tests for protocol members (#17550) [red-knot] Assignability for subclasses of `Any` and `Unknown` (#17557) [red-knot] mypy_primer: add strawberry, print compilation errors to stderr (#17578) [red-knot] GenericAlias instances as a base class (#17575) Remove redundant `type_to_visitor_function` entries (#17564) Fixes how the checker visits `typing.cast`/`typing.NewType` arguments (#17538) [red-knot] Class literal `__new__` function callable subtyping (#17533) [red-knot] Surround intersections with `()` in potentially ambiguous contexts (#17568) [minor] Delete outdated TODO comment (#17565) [red-knot] add regression test for fixed cycle panic (#17535) [red-knot] fix unions of literals, again (#17534) red_knot_python_semantic: remove last vestige of old diagnostics! red_knot_python_semantic: migrate `types` to new diagnostics red_knot_python_semantic: migrate `types/diagnostic` to new diagnostics red_knot_python_semantic: migrate `types/call/bind` to new diagnostics red_knot_python_semantic: migrate `types/string_annotation` to new diagnostics red_knot_python_semantic: migrate `types/infer` to new diagnostic model red_knot_python_semantic: migrate INVALID_ASSIGNMENT for inference ...

…var-instance * dcreager/generic-constructor: (29 commits) We don't need this [red-knot] Make `BoundMethodType` a salsa interned (#17581) [red-knot] Emit a diagnostic if a non-protocol is passed to `get_protocol_members` (#17551) [red-knot] Add more tests for protocol members (#17550) [red-knot] Assignability for subclasses of `Any` and `Unknown` (#17557) [red-knot] mypy_primer: add strawberry, print compilation errors to stderr (#17578) [red-knot] GenericAlias instances as a base class (#17575) Remove redundant `type_to_visitor_function` entries (#17564) Fixes how the checker visits `typing.cast`/`typing.NewType` arguments (#17538) [red-knot] Class literal `__new__` function callable subtyping (#17533) [red-knot] Surround intersections with `()` in potentially ambiguous contexts (#17568) [minor] Delete outdated TODO comment (#17565) [red-knot] add regression test for fixed cycle panic (#17535) [red-knot] fix unions of literals, again (#17534) red_knot_python_semantic: remove last vestige of old diagnostics! red_knot_python_semantic: migrate `types` to new diagnostics red_knot_python_semantic: migrate `types/diagnostic` to new diagnostics red_knot_python_semantic: migrate `types/call/bind` to new diagnostics red_knot_python_semantic: migrate `types/string_annotation` to new diagnostics red_knot_python_semantic: migrate `types/infer` to new diagnostic model ...

MatthewMckee4 added 2 commits April 22, 2025 00:01

Add inital new symbol function lookup

ba52d1d

Implement class literal with __new__ subtyping of callables

3c17670

MatthewMckee4 requested review from AlexWaygood, carljm, dcreager and sharkdp as code owners April 21, 2025 23:21

carljm reviewed Apr 22, 2025

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MatthewMckee4 and others added 2 commits April 22, 2025 01:34

Update types.rs

e4bf1f7

Co-authored-by: Carl Meyer <carl@oddbird.net>

Update is_subtype_of.md

519dacb

Co-authored-by: Carl Meyer <carl@oddbird.net>

MatthewMckee4 commented Apr 22, 2025

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MatthewMckee4 added 2 commits April 22, 2025 01:50

Update is_subtype_of.md

24e63fa

Update types.rs

f5c0a8e

MichaReiser added the ty Multi-file analysis & type inference label Apr 22, 2025

Fix pre-commit

1fc7bf0

AlexWaygood reviewed Apr 22, 2025

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MatthewMckee4 mentioned this pull request Apr 22, 2025

Add playground workspace package-lock.json to gitignore #17466

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Remove lockfile

a3ab945

dhruvmanila approved these changes Apr 22, 2025

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MatthewMckee4 added 2 commits April 22, 2025 18:58

Refactor

c3dd673

Merge branch 'main' into class-literal-new-function-callable-subtyping

0745192

MatthewMckee4 commented Apr 22, 2025

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carljm approved these changes Apr 23, 2025

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carljm merged commit e45f23b into astral-sh:main Apr 23, 2025
34 checks passed

MatthewMckee4 deleted the class-literal-new-function-callable-subtyping branch April 25, 2025 20:55

dhruvmanila mentioned this pull request May 2, 2025

Add subtyping / assignability between callable types and classes astral-sh/ty#129

Closed

4 tasks

		let new_function = new_function.into_bound_method_type(db, self);
		return new_function.is_subtype_of(db, target);

	let new_function = new_function.into_bound_method_type(db, self);
	return new_function.is_subtype_of(db, target);
	return new_function.into_bound_method_type(db, self).is_subtype_of(db, target);

[red-knot] Class literal __new__ function callable subtyping #17533

[red-knot] Class literal __new__ function callable subtyping #17533

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MatthewMckee4 commented Apr 21, 2025

Summary

Test Plan

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[red-knot] Class literal `new` function callable subtyping #17533

[red-knot] Class literal `new` function callable subtyping #17533

github-actions bot commented Apr 21, 2025 •

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