Introspection: make __new__ return the type and not None

newsfragments/5555.changed.md

@@ -0,0 +1 @@
+Introspection: fix `__new__` return type to be the built object type and not `None`

pyo3-macros-backend/src/pyimpl.rs

@@ -18,13 +18,13 @@ use crate::{
 };
 use proc_macro2::TokenStream;
 use quote::{format_ident, quote};
-#[cfg(feature = "experimental-inspect")]
-use syn::Ident;
 use syn::{
     parse::{Parse, ParseStream},
     spanned::Spanned,
     ImplItemFn, Result,
 };
+#[cfg(feature = "experimental-inspect")]
+use syn::{parse_quote, Ident};
 
 /// The mechanism used to collect `#[pymethods]` into the type object
 #[derive(Copy, Clone)]
@@ -411,7 +411,7 @@ fn method_introspection_code(spec: &FnSpec<'_>, parent: &syn::Type, ctx: &Ctx) -
         }
         FnType::FnNew | FnType::FnNewClass(_) => {
             first_argument = Some("cls");
-            output = syn::ReturnType::Default; // The __new__ Python function return type is None
+            output = parse_quote!(-> #pyo3_path::PyRef<Self>); // Hack to return Self while implementing IntoPyObject
         }
         FnType::FnClass(_) => {
             first_argument = Some("cls");

pytests/stubs/comparisons.pyi

@@ -1,16 +1,16 @@
 class Eq:
     def __eq__(self, /, other: Eq) -> bool: ...
     def __ne__(self, /, other: Eq) -> bool: ...
-    def __new__(cls, /, value: int) -> None: ...
+    def __new__(cls, /, value: int) -> Eq: ...
 
 class EqDefaultNe:
     def __eq__(self, /, other: EqDefaultNe) -> bool: ...
-    def __new__(cls, /, value: int) -> None: ...
+    def __new__(cls, /, value: int) -> EqDefaultNe: ...
 
 class EqDerived:
     def __eq__(self, /, other: EqDerived) -> bool: ...
     def __ne__(self, /, other: EqDerived) -> bool: ...
-    def __new__(cls, /, value: int) -> None: ...
+    def __new__(cls, /, value: int) -> EqDerived: ...
 
 class Ordered:
     def __eq__(self, /, other: Ordered) -> bool: ...
@@ -19,15 +19,15 @@ class Ordered:
     def __le__(self, /, other: Ordered) -> bool: ...
     def __lt__(self, /, other: Ordered) -> bool: ...
     def __ne__(self, /, other: Ordered) -> bool: ...
-    def __new__(cls, /, value: int) -> None: ...
+    def __new__(cls, /, value: int) -> Ordered: ...
 
 class OrderedDefaultNe:
     def __eq__(self, /, other: OrderedDefaultNe) -> bool: ...
     def __ge__(self, /, other: OrderedDefaultNe) -> bool: ...
     def __gt__(self, /, other: OrderedDefaultNe) -> bool: ...
     def __le__(self, /, other: OrderedDefaultNe) -> bool: ...
     def __lt__(self, /, other: OrderedDefaultNe) -> bool: ...
-    def __new__(cls, /, value: int) -> None: ...
+    def __new__(cls, /, value: int) -> OrderedDefaultNe: ...
 
 class OrderedDerived:
     def __eq__(self, /, other: OrderedDerived) -> bool: ...
@@ -37,7 +37,7 @@ class OrderedDerived:
     def __le__(self, /, other: OrderedDerived) -> bool: ...
     def __lt__(self, /, other: OrderedDerived) -> bool: ...
     def __ne__(self, /, other: OrderedDerived) -> bool: ...
-    def __new__(cls, /, value: int) -> None: ...
+    def __new__(cls, /, value: int) -> OrderedDerived: ...
     def __str__(self, /) -> str: ...
 
 class OrderedRichCmp:
@@ -47,4 +47,4 @@ class OrderedRichCmp:
     def __le__(self, /, other: OrderedRichCmp) -> bool: ...
     def __lt__(self, /, other: OrderedRichCmp) -> bool: ...
     def __ne__(self, /, other: OrderedRichCmp) -> bool: ...
-    def __new__(cls, /, value: int) -> None: ...
+    def __new__(cls, /, value: int) -> OrderedRichCmp: ...

pytests/stubs/pyclasses.pyi

@@ -2,10 +2,10 @@ from _typeshed import Incomplete
 from typing import Any
 
 class AssertingBaseClass:
-    def __new__(cls, /, expected_type: Any) -> None: ...
+    def __new__(cls, /, expected_type: Any) -> AssertingBaseClass: ...
 
 class ClassWithDecorators:
-    def __new__(cls, /) -> None: ...
+    def __new__(cls, /) -> ClassWithDecorators: ...
     @property
     def attr(self, /) -> int: ...
     @attr.setter
@@ -19,13 +19,13 @@ class ClassWithDecorators:
     def static_method() -> int: ...
 
 class ClassWithDict:
-    def __new__(cls, /) -> None: ...
+    def __new__(cls, /) -> ClassWithDict: ...
 
 class ClassWithoutConstructor: ...
 
 class EmptyClass:
     def __len__(self, /) -> int: ...
-    def __new__(cls, /) -> None: ...
+    def __new__(cls, /) -> EmptyClass: ...
     def method(self, /) -> None: ...
 
 class PlainObject:
@@ -39,11 +39,11 @@ class PlainObject:
     def foo(self, /, value: str) -> None: ...
 
 class PyClassIter:
-    def __new__(cls, /) -> None: ...
+    def __new__(cls, /) -> PyClassIter: ...
     def __next__(self, /) -> int: ...
 
 class PyClassThreadIter:
-    def __new__(cls, /) -> None: ...
+    def __new__(cls, /) -> PyClassThreadIter: ...
     def __next__(self, /) -> int: ...
 
 def map_a_class(