From f2120591b0051d4239de73960709248456e884e7 Mon Sep 17 00:00:00 2001
From: HampusM <hampus@hampusmat.com>
Date: Thu, 11 Apr 2024 19:03:11 +0200
Subject: feat(ecs-macros): add drop_last attribute to Sole derive macro

---
 ecs-macros/src/lib.rs | 69 +++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 58 insertions(+), 11 deletions(-)

(limited to 'ecs-macros')

diff --git a/ecs-macros/src/lib.rs b/ecs-macros/src/lib.rs
index 73709e4..dcc6d99 100644
--- a/ecs-macros/src/lib.rs
+++ b/ecs-macros/src/lib.rs
@@ -37,7 +37,9 @@ pub fn component_derive(input: TokenStream) -> TokenStream
 
     let item_ident = item.ident();
 
-    let component_attr = item.component_attribute().unwrap_or_default();
+    let component_attr = item
+        .attribute::<ComponentAttribute>("component")
+        .unwrap_or_default();
 
     let drop_last = component_attr.drop_last;
 
@@ -46,7 +48,8 @@ pub fn component_derive(input: TokenStream) -> TokenStream
     quote! {
         impl #ecs_path::component::Component for #item_ident
         {
-            fn drop_last(&self) -> bool {
+            fn drop_last(&self) -> bool
+            {
                 #drop_last
             }
 
@@ -74,18 +77,27 @@ pub fn component_derive(input: TokenStream) -> TokenStream
     .into()
 }
 
-#[proc_macro_derive(Sole)]
+#[proc_macro_derive(Sole, attributes(sole))]
 pub fn sole_derive(input: TokenStream) -> TokenStream
 {
     let item: TypeItem = parse::<Item>(input).unwrap().try_into().unwrap();
 
     let item_ident = item.ident();
 
+    let sole_attr = item.attribute::<SoleAttribute>("sole").unwrap_or_default();
+
+    let drop_last = sole_attr.drop_last;
+
     let ecs_path = find_engine_ecs_crate_path().unwrap_or_else(|| syn_path!(ecs));
 
     quote! {
         impl #ecs_path::sole::Sole for #item_ident
         {
+            fn drop_last(&self) -> bool
+            {
+                #drop_last
+            }
+
             fn as_any_mut(&mut self) -> &mut dyn std::any::Any
             {
                 self
@@ -108,6 +120,11 @@ pub fn sole_derive(input: TokenStream) -> TokenStream
     .into()
 }
 
+trait FromAttribute: Sized
+{
+    fn from_attribute(attribute: &Attribute) -> Result<Self, syn::Error>;
+}
+
 enum TypeItem
 {
     Struct(ItemStruct),
@@ -126,7 +143,7 @@ impl TypeItem
         }
     }
 
-    fn component_attribute(&self) -> Option<ComponentAttribute>
+    fn attribute<Attr: FromAttribute>(&self, attr_ident: &str) -> Option<Attr>
     {
         let item_attrs = match &self {
             Self::Struct(struct_item) => &struct_item.attrs,
@@ -134,19 +151,19 @@ impl TypeItem
             &Self::Union(union_item) => &union_item.attrs,
         };
 
-        let mut component_attr: Option<&Attribute> = None;
+        let mut attr: Option<&Attribute> = None;
 
         for item_attr in item_attrs {
-            if component_attr.is_some() {
-                panic!("Expected only one component attribute");
+            if attr.is_some() {
+                panic!("Expected only one {} attribute", attr_ident);
             }
 
-            if item_attr.path().get_ident()? == "component" {
-                component_attr = Some(item_attr);
+            if item_attr.path().get_ident()? == attr_ident {
+                attr = Some(item_attr);
             }
         }
 
-        Some(ComponentAttribute::from_attribute(component_attr?).unwrap())
+        Some(Attr::from_attribute(attr?).unwrap())
     }
 }
 
@@ -186,7 +203,37 @@ struct ComponentAttribute
     drop_last: bool,
 }
 
-impl ComponentAttribute
+impl FromAttribute for ComponentAttribute
+{
+    fn from_attribute(attribute: &Attribute) -> Result<Self, syn::Error>
+    {
+        let mut drop_last = false;
+
+        attribute.parse_nested_meta(|meta| {
+            if meta
+                .path
+                .get_ident()
+                .is_some_and(|flag| flag == "drop_last")
+            {
+                drop_last = true;
+
+                return Ok(());
+            }
+
+            Err(meta.error("Unrecognized token"))
+        })?;
+
+        Ok(Self { drop_last })
+    }
+}
+
+#[derive(Debug, Default)]
+struct SoleAttribute
+{
+    drop_last: bool,
+}
+
+impl FromAttribute for SoleAttribute
 {
     fn from_attribute(attribute: &Attribute) -> Result<Self, syn::Error>
     {
-- 
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