From 78d1343583c2369cec646e844f00d8e915491aaa Mon Sep 17 00:00:00 2001
From: Ibraheem Ahmed <ibraheem@ibraheem.ca>
Date: Thu, 15 Jan 2026 15:42:16 -0500
Subject: [PATCH] [ty] Infer implicit type of `cls` in `__new__` methods
 (#22584)

## Summary

Resolves https://github.com/astral-sh/ty/issues/2489.
---
 .../resources/mdtest/annotations/self.md                  | 4 ++--
 .../ty_python_semantic/resources/mdtest/bidirectional.md  | 2 +-
 .../resources/mdtest/call/constructor.md                  | 2 +-
 crates/ty_python_semantic/src/types/infer/builder.rs      | 8 ++------
 4 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/crates/ty_python_semantic/resources/mdtest/annotations/self.md b/crates/ty_python_semantic/resources/mdtest/annotations/self.md
index 32fd3930cf..32c210a130 100644
--- a/crates/ty_python_semantic/resources/mdtest/annotations/self.md
+++ b/crates/ty_python_semantic/resources/mdtest/annotations/self.md
@@ -585,8 +585,8 @@ class Baz(Bar[Self]): ...
 
 class MyMetaclass(type):
     # TODO: reject the Self usage. because self cannot be used within a metaclass.
-    def __new__(cls) -> Self:
-        return super().__new__(cls)
+    def __new__(cls, name, bases, dct) -> Self:
+        return cls(name, bases, dct)
 ```
 
 ## Explicit annotations override implicit `Self`
diff --git a/crates/ty_python_semantic/resources/mdtest/bidirectional.md b/crates/ty_python_semantic/resources/mdtest/bidirectional.md
index c9c6a5c065..6e773ffbe7 100644
--- a/crates/ty_python_semantic/resources/mdtest/bidirectional.md
+++ b/crates/ty_python_semantic/resources/mdtest/bidirectional.md
@@ -271,7 +271,7 @@ def f[T](x: T) -> list[T]:
 
 class A:
     def __new__(cls, value: list[int | str]):
-        return super().__new__(cls, value)
+        return super().__new__(cls)
 
     def __init__(self, value: list[int | None]): ...
 
diff --git a/crates/ty_python_semantic/resources/mdtest/call/constructor.md b/crates/ty_python_semantic/resources/mdtest/call/constructor.md
index b6e65fcdf2..9416881e4c 100644
--- a/crates/ty_python_semantic/resources/mdtest/call/constructor.md
+++ b/crates/ty_python_semantic/resources/mdtest/call/constructor.md
@@ -76,7 +76,7 @@ from typing_extensions import Self
 
 class Base:
     def __new__(cls, x: int) -> Self:
-        return cls()
+        return cls(x)
 
 class Foo(Base): ...
 
diff --git a/crates/ty_python_semantic/src/types/infer/builder.rs b/crates/ty_python_semantic/src/types/infer/builder.rs
index 34e8133b42..1aa6555b3e 100644
--- a/crates/ty_python_semantic/src/types/infer/builder.rs
+++ b/crates/ty_python_semantic/src/types/infer/builder.rs
@@ -101,7 +101,7 @@ use crate::types::diagnostic::{
 use crate::types::enums::is_enum_class_by_inheritance;
 use crate::types::function::{
     FunctionDecorators, FunctionLiteral, FunctionType, KnownFunction, OverloadLiteral,
-    is_implicit_classmethod, is_implicit_staticmethod,
+    is_implicit_classmethod,
 };
 use crate::types::generics::{
     GenericContext, InferableTypeVars, LegacyGenericBase, SpecializationBuilder, bind_typevar,
@@ -2915,10 +2915,6 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         let function_node = function_definition.node(self.module());
         let function_name = &function_node.name;
 
-        if is_implicit_staticmethod(function_name) {
-            return None;
-        }
-
         let mut is_classmethod = is_implicit_classmethod(function_name);
         let inference = infer_definition_types(db, method_definition);
         for decorator in &function_node.decorator_list {
@@ -2942,7 +2938,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             .as_class_literal()?;
 
         let typing_self = typing_self(db, self.scope(), Some(method_definition), class_literal);
-        if is_classmethod {
+        if is_classmethod || function_name == "__new__" {
             typing_self
                 .map(|typing_self| SubclassOfType::from(db, SubclassOfInner::TypeVar(typing_self)))
         } else {