Fix ambiguous associated item error (#4725)

* Add test for ambiguous associated item

The `#[pyclass]` macro implements `IntoPyObject` for the annotated enum.
When the enum has any of `Error`, `Output` or `Target` as members, this
clashes with the associated types of `IntoPyObject`.

This also happens when deriving `IntoPyObject` directly.

* Fix #4723: ambiguous associated item in #[pyclass]

This uses the fix described in rust-lang/rust#57644

Also apply fix to `#[derive(IntoPyObject)]`.

newsfragments/4725.fixed.md

@@ -0,0 +1 @@
+Fix `ambiguous_associated_items` lint error in `#[pyclass]` and `#[derive(IntoPyObject)]` macros.

pyo3-macros-backend/src/intopyobject.rs

@@ -512,7 +512,7 @@ impl<'a> Enum<'a> {
         IntoPyObjectImpl {
             types: IntoPyObjectTypes::Opaque {
                 target: quote!(#pyo3_path::types::PyAny),
-                output: quote!(#pyo3_path::Bound<'py, Self::Target>),
+                output: quote!(#pyo3_path::Bound<'py, <Self as #pyo3_path::conversion::IntoPyObject<'py>>::Target>),
                 error: quote!(#pyo3_path::PyErr),
             },
             body: quote! {
@@ -617,7 +617,10 @@ pub fn build_derive_into_pyobject<const REF: bool>(tokens: &DeriveInput) -> Resu
             type Output = #output;
             type Error = #error;
 
-            fn into_pyobject(self, py: #pyo3_path::Python<#lt_param>) -> ::std::result::Result<Self::Output, Self::Error> {
+            fn into_pyobject(self, py: #pyo3_path::Python<#lt_param>) -> ::std::result::Result<
+                <Self as #pyo3_path::conversion::IntoPyObject>::Output,
+                <Self as #pyo3_path::conversion::IntoPyObject>::Error,
+            > {
                 #body
             }
         }

pyo3-macros-backend/src/pyclass.rs

@@ -1072,10 +1072,13 @@ fn impl_complex_enum(
         quote! {
             impl<'py> #pyo3_path::conversion::IntoPyObject<'py> for #cls {
                 type Target = Self;
-                type Output = #pyo3_path::Bound<'py, Self::Target>;
+                type Output = #pyo3_path::Bound<'py, <Self as #pyo3_path::conversion::IntoPyObject<'py>>::Target>;
                 type Error = #pyo3_path::PyErr;
 
-                fn into_pyobject(self, py: #pyo3_path::Python<'py>) -> ::std::result::Result<Self::Output, Self::Error> {
+                fn into_pyobject(self, py: #pyo3_path::Python<'py>) -> ::std::result::Result<
+                    <Self as #pyo3_path::conversion::IntoPyObject>::Output,
+                    <Self as #pyo3_path::conversion::IntoPyObject>::Error,
+                > {
                     match self {
                         #(#match_arms)*
                     }
@@ -2161,10 +2164,13 @@ impl<'a> PyClassImplsBuilder<'a> {
 
                 impl<'py> #pyo3_path::conversion::IntoPyObject<'py> for #cls {
                     type Target = Self;
-                    type Output = #pyo3_path::Bound<'py, Self::Target>;
+                    type Output = #pyo3_path::Bound<'py, <Self as #pyo3_path::conversion::IntoPyObject<'py>>::Target>;
                     type Error = #pyo3_path::PyErr;
 
-                    fn into_pyobject(self, py: #pyo3_path::Python<'py>) -> ::std::result::Result<Self::Output, Self::Error> {
+                    fn into_pyobject(self, py: #pyo3_path::Python<'py>) -> ::std::result::Result<
+                        <Self as #pyo3_path::conversion::IntoPyObject>::Output,
+                        <Self as #pyo3_path::conversion::IntoPyObject>::Error,
+                    > {
                         #pyo3_path::Bound::new(py, self)
                     }
                 }

tests/test_compile_error.rs

@@ -67,4 +67,5 @@ fn test_compile_errors() {
     t.compile_fail("tests/ui/duplicate_pymodule_submodule.rs");
     #[cfg(all(not(Py_LIMITED_API), Py_3_11))]
     t.compile_fail("tests/ui/invalid_base_class.rs");
+    t.pass("tests/ui/ambiguous_associated_items.rs");
 }

tests/ui/ambiguous_associated_items.rs

@@ -0,0 +1,25 @@
+use pyo3::prelude::*;
+
+#[pyclass(eq)]
+#[derive(PartialEq)]
+pub enum SimpleItems {
+    Error,
+    Output,
+    Target,
+}
+
+#[pyclass]
+pub enum ComplexItems {
+    Error(PyObject),
+    Output(PyObject),
+    Target(PyObject),
+}
+
+#[derive(IntoPyObject)]
+enum DeriveItems {
+    Error(PyObject),
+    Output(PyObject),
+    Target(PyObject),
+}
+
+fn main() {}