1 files changed, 67 insertions, 0 deletions
diff --git a/mingling_macros/src/func/register_metadata.rs b/mingling_macros/src/func/register_metadata.rs
new file mode 100644
index 0000000..a1f9965
--- /dev/null
+++ b/mingling_macros/src/func/register_metadata.rs
@@ -0,0 +1,67 @@
+use proc_macro::TokenStream;
+use quote::ToTokens;
+use syn::TypePath;
+use syn::spanned::Spanned;
+
+use crate::METADATA;
+use crate::get_global_set;
+
+/// Parses and registers a metadata mapping of the form
+/// `register_metadata!(EntryGreet, Description)`.
+///
+/// Stores a match-arm-style string entry `Self::EntryGreet => { ... }` that is
+/// later consumed by `program_final_gen!` to generate the `get_metadata`
+/// method of `ProgramCollect`.
+pub(crate) fn register_metadata_impl(input: TokenStream) -> TokenStream {
+    // Parse the input as a comma-separated list of type arguments.
+    let input_parsed = syn::parse_macro_input!(
+        input with syn::punctuated::Punctuated<syn::Expr, syn::Token![,]>::parse_terminated
+    );
+
+    if input_parsed.len() != 2 {
+        return syn::Error::new(
+            input_parsed.span(),
+            "Expected exactly two comma-separated arguments: `EntryVariant, MetadataType`",
+        )
+        .to_compile_error()
+        .into();
+    }
+
+    let entry_expr = &input_parsed[0];
+    let metadata_expr = &input_parsed[1];
+
+    let entry_type = match syn::parse2::<TypePath>(entry_expr.to_token_stream()) {
+        Ok(ty) => ty,
+        Err(e) => return e.to_compile_error().into(),
+    };
+    let metadata_type = match syn::parse2::<TypePath>(metadata_expr.to_token_stream()) {
+        Ok(ty) => ty,
+        Err(e) => return e.to_compile_error().into(),
+    };
+
+    let entry_str = build_metadata_entry(&entry_type, &metadata_type).to_string();
+
+    get_global_set(&METADATA).lock().unwrap().insert(entry_str);
+
+    quote::quote! {}.into()
+}
+
+/// Builds the match-arm entry for `get_metadata`, matching on the enum variant
+/// and then on the requested `TypeId`.
+fn build_metadata_entry(
+    entry_type: &TypePath,
+    metadata_type: &TypePath,
+) -> proc_macro2::TokenStream {
+    let enum_variant = entry_type.path.segments.last().unwrap().ident.clone();
+    quote::quote! {
+        Self::#enum_variant => {
+            let __metadata_type_id = ::std::any::TypeId::of::<#metadata_type>();
+            match type_id {
+                _ if type_id == __metadata_type_id => Some(::std::boxed::Box::new(
+                    <#entry_type as ::mingling::Metadata<#metadata_type>>::init_metadata(),
+                ) as ::std::boxed::Box<dyn ::std::any::Any>),
+                _ => None,
+            }
+        }
+    }
+}