fix :

- clippy beta
- better compile error (+related doc and test)

Author: newcomertv

guide/src/class.md

@@ -1183,7 +1183,7 @@ enum BadSubclass {
 
 An enum is complex if it has any non-unit (struct or tuple) variants.
 
-Currently PyO3 supports only struct and tuple variants in a complex enum. Support for unit variants is planned.
+PyO3 supports only struct and tuple variants in a complex enum. Unit variants aren't supported at present (the recommendation is to use an empty tuple enum instead).
 
 PyO3 adds a class attribute for each variant, which may be used to construct values and in match patterns. PyO3 also provides getter methods for all fields of each variant.
 

pyo3-macros-backend/src/pyclass.rs

@@ -505,7 +505,7 @@ impl<'a> PyClassComplexEnum<'a> {
                     Fields::Unit => {
                         bail_spanned!(variant.span() => format!(
                             "Unit variant `{ident}` is not yet supported in a complex enum\n\
-                            = help: change to a struct variant with no fields: `{ident} {{ }}`\n\
+                            = help: change to an empty tuple variant instead: `{ident}()`\n\
                             = note: the enum is complex because of non-unit variant `{witness}`",
                             ident=ident, witness=witness))
                     }
@@ -530,8 +530,7 @@ impl<'a> PyClassComplexEnum<'a> {
                         let fields = types
                             .unnamed
                             .iter()
-                            .enumerate()
-                            .map(|(_i, field)| PyClassEnumVariantUnnamedField {
+                            .map(|field| PyClassEnumVariantUnnamedField {
                                 ty: &field.ty,
                                 span: field.span(),
                             })

tests/ui/invalid_pyclass_enum.stderr

@@ -17,7 +17,7 @@ error: #[pyclass] can't be used on enums without any variants
    |                  ^^
 
 error: Unit variant `UnitVariant` is not yet supported in a complex enum
-       = help: change to a struct variant with no fields: `UnitVariant { }`
+       = help: change to an empty tuple variant instead: `UnitVariant()`
        = note: the enum is complex because of non-unit variant `StructVariant`
   --> tests/ui/invalid_pyclass_enum.rs:21:5
    |