Fix #149 - mutators for generic fields

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Fixed
+- Fix mutators for generic fields (see issue #149)
 
 ## 0.19.0 - 2024-06-15
 ### Added

tests/tests.rs

@@ -936,3 +936,21 @@ fn test_mutators_field() {
     let foo = Foo::builder().x(1).y(1).inc_y_by_x().build();
     assert_eq!(foo, Foo { x: 1, y: 2, z: 2, w: 2 });
 }
+
+#[test]
+fn test_mutators_for_generic_fields() {
+    use core::ops::AddAssign;
+
+    #[derive(Debug, PartialEq, TypedBuilder)]
+    struct Foo<S: Default + AddAssign, T: Default + AddAssign> {
+        #[builder(via_mutators, mutators(
+            fn x_plus(self, plus: S) {
+                self.x += plus;
+            }
+        ))]
+        x: S,
+        y: T,
+    }
+
+    assert_eq!(Foo::builder().x_plus(1).y(2).build(), Foo { x: 1, y: 2 });
+}

typed-builder-macro/src/struct_info.rs

@@ -6,8 +6,8 @@ use crate::builder_attr::{IntoSetting, TypeBuilderAttr};
 use crate::field_info::FieldInfo;
 use crate::mutator::Mutator;
 use crate::util::{
-    empty_type, empty_type_tuple, first_visibility, modify_types_generics_hack, public_visibility, strip_raw_ident_prefix,
-    type_tuple,
+    empty_type, empty_type_tuple, first_visibility, modify_types_generics_hack, phantom_data_for_generics, public_visibility,
+    strip_raw_ident_prefix, type_tuple,
 };
 
 #[derive(Debug)]
@@ -103,17 +103,7 @@ impl<'a> StructInfo<'a> {
         let generics_with_empty = modify_types_generics_hack(&ty_generics, |args| {
             args.push(syn::GenericArgument::Type(init_fields_type.clone().into()));
         });
-        let phantom_generics = self.generics.params.iter().filter_map(|param| match param {
-            syn::GenericParam::Lifetime(lifetime) => {
-                let lifetime = &lifetime.lifetime;
-                Some(quote!(&#lifetime ()))
-            }
-            syn::GenericParam::Type(ty) => {
-                let ty = &ty.ident;
-                Some(ty.to_token_stream())
-            }
-            syn::GenericParam::Const(_cnst) => None,
-        });
+        let phantom_data = phantom_data_for_generics(self.generics);
 
         let builder_method_name = self.builder_attr.builder_method.get_name().unwrap_or_else(|| quote!(builder));
         let builder_method_visibility = first_visibility(&[
@@ -193,7 +183,7 @@ impl<'a> StructInfo<'a> {
             #[allow(dead_code, non_camel_case_types, non_snake_case)]
             #builder_type_visibility struct #builder_name #b_generics #b_generics_where_extras_predicates {
                 fields: #all_fields_param,
-                phantom: ::core::marker::PhantomData<(#( ::core::marker::PhantomData<#phantom_generics> ),*)>,
+                phantom: #phantom_data,
             }
 
             #[automatically_derived]
@@ -472,24 +462,33 @@ impl<'a> StructInfo<'a> {
         let fn_name = &sig.ident;
         let mutator_args = mutator.arguments();
 
+        // Generics for the mutator - should be similar to the struct's generics
+        let m_generics = &self.generics;
+        let (m_impl_generics, m_ty_generics, m_where_clause) = m_generics.split_for_impl();
+        let m_phantom = phantom_data_for_generics(self.generics);
+
         Ok(quote! {
             #[allow(dead_code, non_camel_case_types, missing_docs)]
             #[automatically_derived]
             impl #impl_generics #builder_name <#ty_generics> #where_clause {
                 #(#attrs)*
                 #[allow(clippy::used_underscore_binding, clippy::no_effect_underscore_binding)]
                 #vis #sig {
-                    struct #mutator_struct_name {
+                    struct #mutator_struct_name #m_generics #m_where_clause {
+                        __phantom: #m_phantom,
                         #mutator_ty_fields
                     }
-                    impl #mutator_struct_name {
+                    impl #m_impl_generics #mutator_struct_name #m_ty_generics #m_where_clause {
                         #mutator_fn
                     }
 
                     let __args = (#mutator_args);
 
                     let ( #destructuring ) = self.fields;
-                    let mut __mutator = #mutator_struct_name{ #mutator_destructure_fields };
+                    let mut __mutator: #mutator_struct_name #m_ty_generics = #mutator_struct_name {
+                        __phantom: ::core::default::Default::default(),
+                        #mutator_destructure_fields
+                    };
 
                     // This dance is required to keep mutator args and destrucutre fields from interfering.
                     {
@@ -498,6 +497,7 @@ impl<'a> StructInfo<'a> {
                     }
 
                     let #mutator_struct_name {
+                        __phantom,
                         #mutator_destructure_fields
                     } = __mutator;
 

typed-builder-macro/src/util.rs

@@ -1,7 +1,7 @@
 use std::iter;
 
 use proc_macro2::{Ident, Span, TokenStream, TokenTree};
-use quote::{format_ident, ToTokens};
+use quote::{format_ident, quote, ToTokens};
 use syn::{
     parenthesized,
     parse::{Parse, ParseStream, Parser},
@@ -357,3 +357,18 @@ pub fn pat_to_ident(i: usize, pat: &Pat) -> Ident {
         format_ident!("__{i}", span = pat.span())
     }
 }
+
+pub fn phantom_data_for_generics(generics: &syn::Generics) -> proc_macro2::TokenStream {
+    let phantom_generics = generics.params.iter().filter_map(|param| match param {
+        syn::GenericParam::Lifetime(lifetime) => {
+            let lifetime = &lifetime.lifetime;
+            Some(quote!(&#lifetime ()))
+        }
+        syn::GenericParam::Type(ty) => {
+            let ty = &ty.ident;
+            Some(ty.to_token_stream())
+        }
+        syn::GenericParam::Const(_cnst) => None,
+    });
+    quote!(::core::marker::PhantomData<(#( ::core::marker::PhantomData<#phantom_generics> ),*)>)
+}