Avoid clippy::useless_conversion lint in macros

newsfragments/4944.fixed.md

@@ -0,0 +1 @@
+Fixes unintentional `clippy::useless_conversion` trigger by adjusting macro hygiene.

pyo3-macros-backend/src/method.rs

@@ -265,26 +265,20 @@ impl FnType {
                 let slf: Ident = syn::Ident::new("_slf", Span::call_site());
                 let pyo3_path = pyo3_path.to_tokens_spanned(*span);
                 let ret = quote_spanned! { *span =>
-                    #[allow(clippy::useless_conversion)]
-                    ::std::convert::Into::into(
-                        #pyo3_path::impl_::pymethods::BoundRef::ref_from_ptr(#py, &*(&#slf as *const _ as *const *mut _))
-                            .downcast_unchecked::<#pyo3_path::types::PyType>()
-                    )
+                    #pyo3_path::impl_::pymethods::BoundRef::ref_from_ptr(#py, &*(&#slf as *const _ as *const *mut _))
+                        .downcast_unchecked::<#pyo3_path::types::PyType>()
                 };
-                Some(quote! { unsafe { #ret }, })
+                Some(quote! { unsafe { ::std::convert::Into::into(#ret) }, })
             }
             FnType::FnModule(span) => {
                 let py = syn::Ident::new("py", Span::call_site());
                 let slf: Ident = syn::Ident::new("_slf", Span::call_site());
                 let pyo3_path = pyo3_path.to_tokens_spanned(*span);
                 let ret = quote_spanned! { *span =>
-                    #[allow(clippy::useless_conversion)]
-                    ::std::convert::Into::into(
-                        #pyo3_path::impl_::pymethods::BoundRef::ref_from_ptr(#py, &*(&#slf as *const _ as *const *mut _))
-                            .downcast_unchecked::<#pyo3_path::types::PyModule>()
-                    )
+                    #pyo3_path::impl_::pymethods::BoundRef::ref_from_ptr(#py, &*(&#slf as *const _ as *const *mut _))
+                        .downcast_unchecked::<#pyo3_path::types::PyModule>()
                 };
-                Some(quote! { unsafe { #ret }, })
+                Some(quote! { unsafe { ::std::convert::Into::into(#ret) }, })
             }
             FnType::FnNew | FnType::FnStatic | FnType::ClassAttribute => None,
         }

pyo3-macros-backend/src/quotes.rs

@@ -15,10 +15,10 @@ pub(crate) fn ok_wrap(obj: TokenStream, ctx: &Ctx) -> TokenStream {
         output_span,
     } = ctx;
     let pyo3_path = pyo3_path.to_tokens_spanned(*output_span);
+    let into = quote!(::core::convert::Into::<#pyo3_path::PyErr>::into);
     quote_spanned! { *output_span => {
         let obj = #obj;
-        #[allow(clippy::useless_conversion)]
-        #pyo3_path::impl_::wrap::converter(&obj).wrap(obj).map_err(::core::convert::Into::<#pyo3_path::PyErr>::into)
+        #pyo3_path::impl_::wrap::converter(&obj).wrap(obj).map_err(#into)
     }}
 }
 

tests/ui/invalid_pyfunctions.stderr

@@ -43,6 +43,9 @@ error: expected `&PyModule` or `Py<PyModule>` as first argument with `pass_modul
 error[E0277]: the trait bound `&str: From<BoundRef<'_, '_, pyo3::types::PyModule>>` is not satisfied
   --> tests/ui/invalid_pyfunctions.rs:33:14
    |
+31 | #[pyfunction(pass_module)]
+   | -------------------------- required by a bound introduced by this call
+32 | fn first_argument_not_module<'a, 'py>(
 33 |     _string: &str,
    |              ^ the trait `From<BoundRef<'_, '_, pyo3::types::PyModule>>` is not implemented for `&str`
    |

tests/ui/invalid_pymethods.stderr

@@ -182,6 +182,9 @@ error: macros cannot be used as items in `#[pymethods]` impl blocks
 error[E0277]: the trait bound `i32: From<BoundRef<'_, '_, PyType>>` is not satisfied
   --> tests/ui/invalid_pymethods.rs:46:45
    |
+43 | #[pymethods]
+   | ------------ required by a bound introduced by this call
+...
 46 |     fn classmethod_wrong_first_argument(_x: i32) -> Self {
    |                                             ^^^ the trait `From<BoundRef<'_, '_, PyType>>` is not implemented for `i32`
    |

tests/ui/invalid_result_conversion.stderr

@@ -15,3 +15,22 @@ error[E0277]: the trait bound `PyErr: From<MyError>` is not satisfied
              `PyErr` implements `From<IntoInnerError<W>>`
            and $N others
    = note: required for `MyError` to implement `Into<PyErr>`
+
+error[E0277]: the trait bound `PyErr: From<MyError>` is not satisfied
+  --> tests/ui/invalid_result_conversion.rs:21:1
+   |
+21 | #[pyfunction]
+   | ^^^^^^^^^^^^^ the trait `From<MyError>` is not implemented for `PyErr`
+   |
+   = help: the following other types implement trait `From<T>`:
+             `PyErr` implements `From<AddrParseError>`
+             `PyErr` implements `From<DecodeUtf16Error>`
+             `PyErr` implements `From<DowncastError<'_, '_>>`
+             `PyErr` implements `From<DowncastIntoError<'_>>`
+             `PyErr` implements `From<FromUtf16Error>`
+             `PyErr` implements `From<FromUtf8Error>`
+             `PyErr` implements `From<Infallible>`
+             `PyErr` implements `From<IntoInnerError<W>>`
+           and $N others
+   = note: required for `MyError` to implement `Into<PyErr>`
+   = note: this error originates in the attribute macro `pyfunction` (in Nightly builds, run with -Z macro-backtrace for more info)