Derive AsChangeset also for the plain struct, similar to Insertable

Address Review comments

Author: weiznich

diesel_derives/src/as_changeset.rs

@@ -30,12 +30,23 @@ pub fn derive(item: syn::DeriveInput) -> Result<quote::Tokens, Diagnostic> {
         .iter()
         .filter(|f| !model.primary_key_names.contains(&f.column_name()))
         .collect::<Vec<_>>();
-    let changeset_ty = fields_for_update
+    let ref_changeset_ty = fields_for_update.iter().map(|field| {
+        field_changeset_ty(
+            field,
+            table_name,
+            treat_none_as_null,
+            Some(quote!(&'update)),
+        )
+    });
+    let ref_changeset_expr = fields_for_update
         .iter()
-        .map(|field| field_changeset_ty(field, table_name, treat_none_as_null));
-    let changeset_expr = fields_for_update
+        .map(|field| field_changeset_expr(field, table_name, treat_none_as_null, Some(quote!(&))));
+    let direct_changeset_ty = fields_for_update
         .iter()
-        .map(|field| field_changeset_expr(field, table_name, treat_none_as_null));
+        .map(|field| field_changeset_ty(field, table_name, treat_none_as_null, None));
+    let direct_changeset_expr = fields_for_update
+        .iter()
+        .map(|field| field_changeset_expr(field, table_name, treat_none_as_null, None));
 
     if fields_for_update.is_empty() {
         Span::call_site()
@@ -57,10 +68,21 @@ pub fn derive(item: syn::DeriveInput) -> Result<quote::Tokens, Diagnostic> {
             #where_clause
             {
                 type Target = #table_name::table;
-                type Changeset = <(#(#changeset_ty,)*) as AsChangeset>::Changeset;
+                type Changeset = <(#(#ref_changeset_ty,)*) as AsChangeset>::Changeset;
+
+                fn as_changeset(self) -> Self::Changeset {
+                    (#(#ref_changeset_expr,)*).as_changeset()
+                }
+            }
+
+            impl #impl_generics AsChangeset for #struct_name #ty_generics
+            #where_clause
+            {
+                type Target = #table_name::table;
+                type Changeset = <(#(#direct_changeset_ty,)*) as AsChangeset>::Changeset;
 
                 fn as_changeset(self) -> Self::Changeset {
-                    (#(#changeset_expr,)*).as_changeset()
+                    (#(#direct_changeset_expr,)*).as_changeset()
                 }
             }
         ),
@@ -71,27 +93,33 @@ fn field_changeset_ty(
     field: &Field,
     table_name: syn::Ident,
     treat_none_as_null: bool,
+    lifetime: Option<quote::Tokens>,
 ) -> syn::Type {
     let column_name = field.column_name();
     if !treat_none_as_null && is_option_ty(&field.ty) {
         let field_ty = inner_of_option_ty(&field.ty);
-        parse_quote!(std::option::Option<diesel::dsl::Eq<#table_name::#column_name, &'update #field_ty>>)
+        parse_quote!(std::option::Option<diesel::dsl::Eq<#table_name::#column_name, #lifetime #field_ty>>)
     } else {
         let field_ty = &field.ty;
-        parse_quote!(diesel::dsl::Eq<#table_name::#column_name, &'update #field_ty>)
+        parse_quote!(diesel::dsl::Eq<#table_name::#column_name, #lifetime #field_ty>)
     }
 }
 
 fn field_changeset_expr(
     field: &Field,
     table_name: syn::Ident,
     treat_none_as_null: bool,
+    lifetime: Option<quote::Tokens>,
 ) -> syn::Expr {
     let field_access = field.name.access();
     let column_name = field.column_name();
     if !treat_none_as_null && is_option_ty(&field.ty) {
-        parse_quote!(self#field_access.as_ref().map(|x| #table_name::#column_name.eq(x)))
+        if lifetime.is_some() {
+            parse_quote!(self#field_access.as_ref().map(|x| #table_name::#column_name.eq(x)))
+        } else {
+            parse_quote!(self#field_access.map(|x| #table_name::#column_name.eq(x)))
+        }
     } else {
-        parse_quote!(#table_name::#column_name.eq(&self#field_access))
+        parse_quote!(#table_name::#column_name.eq(#lifetime self#field_access))
     }
 }