Add the opensmtpd_derive crate

opensmtpd-derive/src/lib.rs

@@ -0,0 +1,18 @@
+use proc_macro::TokenStream;
+use proc_macro2::Span;
+use quote::quote;
+use syn::{parse_macro_input, Ident, ItemFn};
+
+#[proc_macro_attribute]
+pub fn register(_attr: TokenStream, input: TokenStream) -> TokenStream {
+    let item = parse_macro_input!(input as ItemFn);
+    let fn_name = item.sig.ident.to_string().replacen("on_", "has_", 1);
+    let fn_name = Ident::new(&fn_name, Span::call_site());
+    let output = quote! {
+        fn #fn_name(&self) -> bool {
+            true
+        }
+        #item
+    };
+    output.into()
+}