1 files changed, 231 insertions, 0 deletions
diff --git a/mingling_macros/src/attr/help.rs b/mingling_macros/src/attr/help.rs
new file mode 100644
index 0000000..aa7bc88
--- /dev/null
+++ b/mingling_macros/src/attr/help.rs
@@ -0,0 +1,231 @@
+use proc_macro::TokenStream;
+use quote::{ToTokens, quote};
+use syn::spanned::Spanned;
+use syn::{Ident, ItemFn, Pat, ReturnType, Signature, TypePath, parse_macro_input};
+
+use crate::get_global_set;
+use crate::res_injection::{extract_args_info, generate_immut_resource_bindings};
+
+/// Extracts the user's return type, returning `None` for no return type.
+fn extract_user_return_type(sig: &Signature) -> Option<proc_macro2::TokenStream> {
+    match &sig.output {
+        ReturnType::Type(_, ty) => Some(quote! { #ty }),
+        ReturnType::Default => None,
+    }
+}
+
+pub(crate) fn help_attr(item: TokenStream) -> TokenStream {
+    // Parse the function item
+    let input_fn = parse_macro_input!(item as ItemFn);
+
+    // Validate the function is not async
+    if input_fn.sig.asyncness.is_some() {
+        return syn::Error::new(input_fn.sig.span(), "Help function cannot be async")
+            .to_compile_error()
+            .into();
+    }
+
+    // Extract the entry type and resource injection params
+    let (_, entry_type, resources) = match extract_args_info(&input_fn.sig) {
+        Ok(info) => info,
+        Err(e) => return e.to_compile_error().into(),
+    };
+
+    // Determine the user's return type for preserving the original function
+    let user_return_type = extract_user_return_type(&input_fn.sig);
+
+    // Get the function body
+    let fn_body = &input_fn.block;
+    let fn_body_stmts = &fn_body.stmts;
+
+    // Get function attributes excluding the help attribute
+    let mut fn_attrs = input_fn.attrs.clone();
+    fn_attrs.retain(|attr| !attr.path().is_ident("help"));
+
+    // Get function visibility
+    let vis = &input_fn.vis;
+
+    // Get function name
+    let fn_name = &input_fn.sig.ident;
+
+    // Get original inputs to keep the original function
+    let original_inputs = input_fn.sig.inputs.clone();
+    let original_return_type = user_return_type.clone().unwrap_or(quote! { () });
+
+    // Generate internal name using snake_case
+    let internal_name = format!(
+        "__internal_help_{}",
+        just_fmt::snake_case!(fn_name.to_string())
+    );
+    let struct_name = Ident::new(&internal_name, fn_name.span());
+
+    let program_type = crate::default_program_path();
+    let has_resources = !resources.is_empty();
+    let mut_resources: Vec<_> = resources.iter().filter(|r| r.is_mut).collect();
+
+    // Generate immutable resource bindings
+    let immut_resource_stmts = generate_immut_resource_bindings(resources.iter(), &program_type);
+
+    // Build the call to the original function with resource arguments injected
+    let resource_args: Vec<_> = resources
+        .iter()
+        .map(|res| {
+            let var_name = &res.var_name;
+            quote! { #var_name }
+        })
+        .collect();
+
+    // Use a fixed parameter name `prev` for the trait method, regardless of
+    // the user's original parameter name (which may be `_` and cannot be
+    // referenced in expression position).
+    let fixed_prev: Pat = syn::parse_quote!(prev);
+
+    let fn_call = if has_resources {
+        quote! { #fn_name(#fixed_prev, #(#resource_args),*) }
+    } else {
+        quote! { #fn_name(#fixed_prev) }
+    };
+
+    // Wrap the function call with modify_res for mutable resources
+    let inner_call = if mut_resources.is_empty() {
+        fn_call
+    } else {
+        let mut wrapped = fn_call;
+        for res in mut_resources.iter().rev() {
+            let var_name = &res.var_name;
+            let inner_type = &res.inner_type;
+            wrapped = quote! {
+                ::mingling::this::<#program_type>().modify_res(|#var_name: &mut #inner_type| {
+                    #wrapped
+                })
+            };
+        }
+        wrapped
+    };
+
+    let help_render_body = if has_resources {
+        quote! {
+            #(#immut_resource_stmts)*
+            #inner_call
+        }
+    } else {
+        quote! { #inner_call }
+    };
+
+    // Register the help request mapping
+    let help_entry = build_help_entry(&struct_name, &entry_type);
+    let entry_str = help_entry.to_string();
+
+    // Check for duplicate variant before inserting
+    let variant_name = entry_type.path.segments.last().unwrap().ident.to_string();
+    {
+        let helps = get_global_set(&crate::HELP_REQUESTS).lock().unwrap();
+        if let Err(err) = crate::check_duplicate_variant(
+            &helps,
+            &entry_str,
+            &variant_name,
+            "help",
+            entry_type.span(),
+        ) {
+            return err.into();
+        }
+    }
+
+    get_global_set(&crate::HELP_REQUESTS)
+        .lock()
+        .unwrap()
+        .insert(entry_str);
+
+    // Generate the struct and HelpRequest implementation
+    let expanded = quote! {
+        #(#fn_attrs)*
+        #[doc(hidden)]
+        #[allow(non_camel_case_types)]
+        #vis struct #struct_name;
+
+        impl ::mingling::HelpRequest for #struct_name {
+            type Entry = #entry_type;
+
+            fn render_help(#fixed_prev: Self::Entry) -> ::mingling::RenderResult {
+                let __help_result = { #help_render_body };
+                ::std::convert::Into::into(__help_result)
+            }
+        }
+
+        ::mingling::macros::register_help!(#entry_type, #struct_name);
+
+        // Keep the original function unchanged
+        #(#fn_attrs)*
+        #vis fn #fn_name(#original_inputs) -> #original_return_type {
+            #(#fn_body_stmts)*
+        }
+    };
+
+    expanded.into()
+}
+
+/// Builds a help request entry for the global help requests list
+fn build_help_entry(struct_name: &Ident, entry_type: &TypePath) -> proc_macro2::TokenStream {
+    let enum_variant = &entry_type.path.segments.last().unwrap().ident;
+    quote! {
+        Self::#enum_variant => {
+            // SAFETY: The member_id check ensures that `any` contains a value of type `#entry_type`,
+            // so downcasting to `#entry_type` is safe.
+            let value = unsafe { any.downcast::<#entry_type>().unwrap_unchecked() };
+            <#struct_name as ::mingling::HelpRequest>::render_help(value)
+        }
+    }
+}
+
+pub(crate) fn register_help(input: TokenStream) -> TokenStream {
+    // Parse the input as a comma-separated list of arguments
+    let input_parsed = syn::parse_macro_input!(input with syn::punctuated::Punctuated<syn::Expr, syn::Token![,]>::parse_terminated);
+
+    // Check if there are exactly two elements
+    if input_parsed.len() != 2 {
+        return syn::Error::new(
+            input_parsed.span(),
+            "Expected exactly two comma-separated arguments: `EntryType, StructName`",
+        )
+        .to_compile_error()
+        .into();
+    }
+
+    // Extract the two elements
+    let entry_type_expr = &input_parsed[0];
+    let struct_name_expr = &input_parsed[1];
+
+    // Convert expressions to TypePath and Ident
+    let entry_type = match syn::parse2::<TypePath>(entry_type_expr.to_token_stream()) {
+        Ok(ty) => ty,
+        Err(e) => return e.to_compile_error().into(),
+    };
+
+    let struct_name = match syn::parse2::<syn::Ident>(struct_name_expr.to_token_stream()) {
+        Ok(ident) => ident,
+        Err(e) => return e.to_compile_error().into(),
+    };
+
+    // Register the help request mapping
+    let help_entry = build_help_entry(&struct_name, &entry_type);
+    let entry_str = help_entry.to_string();
+
+    // Check if entry was already pre-inserted by `#[help]` attribute
+    let mut helps = get_global_set(&crate::HELP_REQUESTS).lock().unwrap();
+    if helps.contains(&entry_str) {
+        // Already registered by `#[help]`, no duplicate check needed
+        return quote! {}.into();
+    }
+
+    // Check for duplicate variant (different struct, same type)
+    let variant_name = entry_type.path.segments.last().unwrap().ident.to_string();
+    if let Err(err) =
+        crate::check_duplicate_variant(&helps, &entry_str, &variant_name, "help", entry_type.span())
+    {
+        return err.into();
+    }
+
+    helps.insert(entry_str);
+
+    quote! {}.into()
+}