Add the opensmtpd_derive crate

opensmtpd-derive/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "opensmtpd_derive"
+version = "0.3.0"
+authors = ["Rodolphe Bréard <rodolphe@what.tf>"]
+edition = "2018"
+description = "Interface for OpenSMTPD filters"
+keywords = ["opensmtpd", "filter", "mail"]
+documentation = "https://docs.rs/opensmtpd-derive/"
+repository = "https://github.com/breard-r/rust-opensmtpd"
+readme = "README.md"
+license = "MIT OR Apache-2.0"
+include = ["src/**/*", "Cargo.toml", "../LICENSE-*.txt"]
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1.0"
+quote = "1.0"
+syn = { version = "1.0", features = ["full", "extra-traits"] }

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()
+}