store the FnArg ident as a Cow instead of a reference (#4157)

This allow also storing idents that were generated
as part of the macro instead of only ones the were
present in the source code. This is needed for
example in complex enum tuple variants.

Author: Icxolu

pyo3-macros-backend/src/method.rs

@@ -1,3 +1,4 @@
+use std::borrow::Cow;
 use std::fmt::Display;
 
 use proc_macro2::{Span, TokenStream};
@@ -18,7 +19,7 @@ use crate::{
 
 #[derive(Clone, Debug)]
 pub struct RegularArg<'a> {
-    pub name: &'a syn::Ident,
+    pub name: Cow<'a, syn::Ident>,
     pub ty: &'a syn::Type,
     pub from_py_with: Option<FromPyWithAttribute>,
     pub default_value: Option<syn::Expr>,
@@ -28,14 +29,14 @@ pub struct RegularArg<'a> {
 /// Pythons *args argument
 #[derive(Clone, Debug)]
 pub struct VarargsArg<'a> {
-    pub name: &'a syn::Ident,
+    pub name: Cow<'a, syn::Ident>,
     pub ty: &'a syn::Type,
 }
 
 /// Pythons **kwarg argument
 #[derive(Clone, Debug)]
 pub struct KwargsArg<'a> {
-    pub name: &'a syn::Ident,
+    pub name: Cow<'a, syn::Ident>,
     pub ty: &'a syn::Type,
 }
 
@@ -61,7 +62,7 @@ pub enum FnArg<'a> {
 }
 
 impl<'a> FnArg<'a> {
-    pub fn name(&self) -> &'a syn::Ident {
+    pub fn name(&self) -> &syn::Ident {
         match self {
             FnArg::Regular(RegularArg { name, .. }) => name,
             FnArg::VarArgs(VarargsArg { name, .. }) => name,
@@ -98,7 +99,10 @@ impl<'a> FnArg<'a> {
             ..
         }) = self
         {
-            *self = Self::VarArgs(VarargsArg { name, ty });
+            *self = Self::VarArgs(VarargsArg {
+                name: name.clone(),
+                ty,
+            });
             Ok(self)
         } else {
             bail_spanned!(self.name().span() => "args cannot be optional")
@@ -113,7 +117,10 @@ impl<'a> FnArg<'a> {
             ..
         }) = self
         {
-            *self = Self::KwArgs(KwargsArg { name, ty });
+            *self = Self::KwArgs(KwargsArg {
+                name: name.clone(),
+                ty,
+            });
             Ok(self)
         } else {
             bail_spanned!(self.name().span() => "kwargs must be Option<_>")
@@ -159,7 +166,7 @@ impl<'a> FnArg<'a> {
                 }
 
                 Ok(Self::Regular(RegularArg {
-                    name: ident,
+                    name: Cow::Borrowed(ident),
                     ty: &cap.ty,
                     from_py_with,
                     default_value: None,

pyo3-macros-backend/src/pyclass.rs

@@ -1153,7 +1153,7 @@ fn complex_enum_struct_variant_new<'a>(
 
         for field in &variant.fields {
             args.push(FnArg::Regular(RegularArg {
-                name: field.ident,
+                name: Cow::Borrowed(field.ident),
                 ty: field.ty,
                 from_py_with: None,
                 default_value: None,