Add `group!` macro for registering external types

1 files changed, 115 insertions, 0 deletions

diff --git a/mingling_macros/src/group_impl.rs b/mingling_macros/src/group_impl.rs
new file mode 100644
index 0000000..1b765f3
--- /dev/null
+++ b/mingling_macros/src/group_impl.rs
@@ -0,0 +1,115 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::parse::{Parse, ParseStream};
+use syn::{Ident, Path, Result as SynResult, Token, TypePath};
+
+/// Input for the `group!` macro
+///
+/// # Syntax
+///
+/// ```rust,ignore
+/// // Explicit mode: specify both program path and type path
+/// group!(crate::ThisProgram, std::io::Error);
+///
+/// // Implicit mode: only type path, uses default `crate::ThisProgram` as program
+/// group!(std::io::Error);
+/// ```
+enum GroupInput {
+    Explicit {
+        program_path: Path,
+        type_path: TypePath,
+    },
+    Implicit {
+        type_path: TypePath,
+    },
+}
+
+impl Parse for GroupInput {
+    fn parse(input: ParseStream) -> SynResult<Self> {
+        // Parse the first path (could be program path or type path)
+        let first_path: Path = input.parse()?;
+
+        // If followed by a comma, it's explicit mode: Path, TypePath
+        if input.peek(Token![,]) {
+            input.parse::<Token![,]>()?;
+            let type_path: TypePath = input.parse()?;
+            Ok(GroupInput::Explicit {
+                program_path: first_path,
+                type_path,
+            })
+        } else {
+            // Otherwise it's implicit mode: just a type path
+            Ok(GroupInput::Implicit {
+                type_path: TypePath {
+                    qself: None,
+                    path: first_path,
+                },
+            })
+        }
+    }
+}
+
+/// Convert a type path into a valid module name segment
+///
+/// e.g. `std::io::Error` -> `internal_group_std_io_error`
+fn module_name_from_type(type_path: &TypePath) -> Ident {
+    let segments: Vec<String> = type_path
+        .path
+        .segments
+        .iter()
+        .map(|seg| seg.ident.to_string().to_lowercase())
+        .collect();
+    Ident::new(
+        &format!("internal_group_{}", segments.join("_")),
+        proc_macro2::Span::call_site(),
+    )
+}
+
+/// Get the last segment name of a type path (the simple type name)
+///
+/// e.g. `std::io::Error` -> `Error`
+fn type_simple_name(type_path: &TypePath) -> Ident {
+    type_path
+        .path
+        .segments
+        .last()
+        .expect("TypePath must have at least one segment")
+        .ident
+        .clone()
+}
+
+pub fn group_macro(input: TokenStream) -> TokenStream {
+    let input = syn::parse_macro_input!(input as GroupInput);
+
+    let (program_path, type_path) = match input {
+        GroupInput::Explicit {
+            program_path,
+            type_path,
+        } => (quote! { #program_path }, type_path),
+        GroupInput::Implicit { type_path } => (crate::default_program_path(), type_path),
+    };
+
+    // Use the type's simple name as the enum variant identifier
+    let type_name = type_simple_name(&type_path);
+    // Create a unique module name from the full type path
+    let module_name = module_name_from_type(&type_path);
+
+    // Generate the module with the Groupped implementation
+    let expanded = quote! {
+        #[allow(non_camel_case_types)]
+        mod #module_name {
+            use #program_path as __MinglingProgram;
+            use #type_path;
+
+            impl ::mingling::Groupped<__MinglingProgram> for #type_name {
+                fn member_id() -> __MinglingProgram {
+                    __MinglingProgram::#type_name
+                }
+            }
+
+            ::mingling::macros::register_type!(#type_name);
+        }
+    };
+
+    expanded.into()
+}