1 files changed, 24 insertions, 0 deletions
diff --git a/rust_macro/src/lib.rs b/rust_macro/src/lib.rs
new file mode 100644
index 0000000..1d4a5ae
--- /dev/null
+++ b/rust_macro/src/lib.rs
@@ -0,0 +1,24 @@
+/// This is a dumping ground for all proc-macros used by passfish.
+/// There's a corresponding runtime module in the main crate.
+extern crate syn;
+extern crate quote;
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+use quote::quote;
+
+/// Adds a global constant name ENUMTYPE_
+/// Thanks, StackOverflow: https://stackoverflow.com/questions/41637978/how-to-get-the-number-of-elements-variants-in-an-enum-as-a-constant-value
+#[proc_macro_derive(EnumVariantCount)]
+pub fn derive_enum_variant_count(input: TokenStream) -> TokenStream {
+    let syn_item: syn::DeriveInput = syn::parse(input).unwrap();
+    let len = match syn_item.data {
+        syn::Data::Enum(enum_item) => enum_item.variants.len(),
+        _ => panic!("EnumVariantCount only works on Enums"),
+    };
+    let enum_name = syn_item.ident;
+    let result = quote! {
+        impl EnumVariantCount for #enum_name { fn variant_count() -> usize { #len } }
+    };
+    result.into()
+}