add derive order test

research/derive_order/Cargo.toml

@@ -0,0 +1,5 @@
+[workspace]
+members = [
+    "derive_macros",
+    "use_macros",
+]

research/derive_order/derive_macros/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "derive_macros"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = "2.0"
+quote = "1.0"
+proc-macro2 = "1.0"

research/derive_order/derive_macros/src/lib.rs

@@ -0,0 +1,42 @@
+extern crate proc_macro;
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, DeriveInput};
+
+#[proc_macro_derive(First)]
+pub fn derive_first(input: TokenStream) -> TokenStream {
+    let ast = parse_macro_input!(input as DeriveInput);
+    let name = &ast.ident;
+
+    let expanded = quote! {
+        impl First for #name {
+            fn is_first_implemented() -> bool {
+                true
+            }
+        }
+    };
+
+    TokenStream::from(expanded)
+}
+
+#[proc_macro_derive(Second)]
+pub fn derive_second(input: TokenStream) -> TokenStream {
+    let ast = parse_macro_input!(input as DeriveInput);
+    let name = &ast.ident;
+
+    let expanded = quote! {
+        impl Second for #name {
+            fn check_first_is_implemented() -> bool {
+                if <#name as First>::is_first_implemented() {
+                    println!("First is implemented, so Second works!");
+                    true
+                } else {
+                    println!("First is NOT implemented, so Second fails!");
+                    false
+                }
+            }
+        }
+    };
+
+    TokenStream::from(expanded)
+}

research/derive_order/use_macros/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "use_macros"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+derive_macros = { path = "../derive_macros" }

research/derive_order/use_macros/src/lib.rs

@@ -0,0 +1,28 @@
+#[cfg(test)]
+mod tests {
+    use derive_macros::{First, Second};
+
+    trait First {
+        fn is_first_implemented() -> bool;
+    }
+
+    trait Second {
+        fn check_first_is_implemented() -> bool;
+    }
+
+    #[test]
+    fn test_first_second() {
+        #[derive(First, Second)] // <-- This should work correctly.
+        struct MyStruct;
+
+        assert!(<MyStruct as Second>::check_first_is_implemented());
+    }
+
+    #[test]
+    fn test_second_first() {
+        #[derive(Second, First)] // <-- Clarify if this should work or fail.
+        struct MyStruct;
+
+        assert!(<MyStruct as Second>::check_first_is_implemented());
+    }
+}