extract from_py_with parsing into its own module

pyo3-macros-backend/src/attrs.rs

@@ -0,0 +1,27 @@
+use proc_macro2::TokenStream;
+use quote::ToTokens;
+use syn::spanned::Spanned;
+use syn::{Meta, MetaNameValue, Result};
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct FromPyWithAttribute(syn::ExprPath);
+
+impl FromPyWithAttribute {
+    pub fn from_meta(meta: Meta) -> Result<Self> {
+        if let Meta::NameValue(MetaNameValue {
+            lit: syn::Lit::Str(string_literal),
+            ..
+        }) = meta
+        {
+            let expr_path = string_literal.parse::<syn::ExprPath>()?;
+            return Ok(FromPyWithAttribute(expr_path));
+        }
+        bail_spanned!(meta.span() => "expected a name-value: `pyo3(from_py_with = \"func\")` ")
+    }
+}
+
+impl ToTokens for FromPyWithAttribute {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        self.0.to_tokens(tokens)
+    }
+}

pyo3-macros-backend/src/from_pyobject.rs

@@ -1,11 +1,9 @@
+use crate::attrs::FromPyWithAttribute;
 use proc_macro2::TokenStream;
 use quote::quote;
 use syn::punctuated::Punctuated;
 use syn::spanned::Spanned;
-use syn::{
-    parse_quote, Attribute, DataEnum, DeriveInput, Fields, Ident, Meta, MetaList, MetaNameValue,
-    Result,
-};
+use syn::{parse_quote, Attribute, DataEnum, DeriveInput, Fields, Ident, Meta, MetaList, Result};
 
 /// Describes derivation input of an enum.
 #[derive(Debug)]
@@ -320,7 +318,7 @@ impl ContainerAttribute {
 #[derive(Clone, Debug)]
 struct FieldAttributes {
     getter: FieldGetter,
-    from_py_with: Option<syn::ExprPath>,
+    from_py_with: Option<FromPyWithAttribute>,
 }
 
 #[derive(Clone, Debug)]
@@ -418,16 +416,8 @@ impl FieldAttributes {
         bail_spanned!(arg_list.span() => "expected a single literal argument");
     }
 
-    fn from_py_with_arg(meta: Meta) -> syn::Result<syn::ExprPath> {
-        if let Meta::NameValue(MetaNameValue {
-            lit: syn::Lit::Str(string_literal),
-            ..
-        }) = meta
-        {
-            let expr_path = string_literal.parse::<syn::ExprPath>()?;
-            return Ok(expr_path);
-        }
-        bail_spanned!(meta.span() => "expected a name-value: `pyo3(from_py_with = \"func\")` ")
+    fn from_py_with_arg(meta: Meta) -> syn::Result<FromPyWithAttribute> {
+        FromPyWithAttribute::from_meta(meta)
     }
 }
 

pyo3-macros-backend/src/lib.rs

@@ -7,6 +7,7 @@
 #[macro_use]
 mod utils;
 
+mod attrs;
 mod defs;
 mod from_pyobject;
 mod konst;