Use quote to generate the proc-macro output

macro-impl/src/lib.rs

 extern crate proc_macro;
-use std::str::FromStr;
 
 use proc_macro::TokenStream;
-use quote::{ToTokens};
-use syn::{ReturnType, parse_macro_input};
-
-fn wrap_function(token_stream: TokenStream, attr: TokenStream) -> TokenStream {
-    let mut function = parse_macro_input!(token_stream as syn::ItemFn);
-
-    let output = function.sig.output;
-    function.sig.output = ReturnType::Default;
-
-    //let prepend = format!("match || {} {{ ", output.to_token_stream().to_string());
-    //let append = "}() { Ok(_) => {}, Err(err) => println!(\"{}\", err), }";
-    let prepend = format!("crate::error::handle_system_result(|| {} {{ ", output.to_token_stream().to_string());
-    let append = "})";
-    
-    let mut function_block_str = function.block.to_token_stream().to_string();
-    function_block_str.insert_str(1, &prepend);
-    function_block_str.insert_str(function_block_str.len() - 2, append);
-    println!("{}", function_block_str);
-    let function_block_token_stream = TokenStream::from_str(&function_block_str).unwrap();
-    let function_block = parse_macro_input!(function_block_token_stream as syn::Block);
-    function.block = Box::new(function_block);
-
-    let attr_str: String = attr.to_string();
-
-    let legion_system_str = if attr_str.is_empty() { 
-            "#[legion::system]".to_string()
-        } else { 
-            format!("#[legion::system({})]", attr_str)
-        };
-
-    let new_function_string = format!("{} {}", legion_system_str, function.to_token_stream().to_string());
-    println!("{}", new_function_string);
-
-    TokenStream::from_str(&new_function_string).unwrap()
-}
 
 #[proc_macro_attribute]
-pub fn angel_system(attr: TokenStream, item: TokenStream) -> TokenStream {
-    println!("attr: \"{}\"", attr.to_string());
-    println!("item: \"{}\"", item.to_string());
-    wrap_function(item, attr)
+pub fn angel_system(args: TokenStream, input: TokenStream) -> TokenStream {
+    let f = syn::parse_macro_input!(input as syn::ItemFn);
+
+    let fname = f.sig.ident;
+    let attrs = f.attrs;
+    let inputs = f.sig.inputs;
+    let block = f.block;
+    let stmts = block.stmts;
+    let rtype = f.sig.output;
+    let vis = f.vis;
+
+    let legion_attr = if !args.is_empty() {
+        let args: proc_macro2::TokenStream = args.into();
+        quote::quote!(#[legion::system(#args)])
+    } else {
+        quote::quote!(#[legion::system])
+    };
+
+    quote::quote!(
+        #legion_attr
+        #(#attrs)*
+        #vis fn #fname(#inputs) {
+            crate::error::handle_system_result(|| #rtype {
+                #(#stmts)*
+            });
+        }
+    )
+    .into()
 }