Simplify Iris app initialization and task updates

macro/src/lib.rs

@@ -9,13 +9,15 @@ use syn::{
     spanned::Spanned,
 };
 
-/// Marks the factory called when Android creates an Iris view.
+/// Marks the initializer called when Android creates an Iris view.
 ///
 /// An attribute is necessary here because the Android loader requires one
 /// exported `JNI_OnLoad` symbol and `android-view` requires a plain function
-/// pointer monomorphized for the returned application state. The generated
-/// linker and JNI glue is Android-gated; the annotated function therefore
-/// does not need its own `cfg` attribute.
+/// pointer monomorphized for the application state. A function returning a
+/// custom state remains its factory; a function with no return value receives
+/// `&mut AndroidUiState` and uses that state directly. The generated linker and
+/// JNI glue is Android-gated; the annotated function therefore does not need
+/// its own `cfg` attribute.
 #[proc_macro_attribute]
 pub fn app_init(args: TokenStream, item: TokenStream) -> TokenStream {
     if !args.is_empty() {
@@ -29,13 +31,9 @@ pub fn app_init(args: TokenStream, item: TokenStream) -> TokenStream {
 
     let function = parse_macro_input!(item as ItemFn);
     let name = &function.sig.ident;
-    let ReturnType::Type(_, state) = &function.sig.output else {
-        return Error::new(
-            function.sig.output.span(),
-            "an app_init function must return its application state",
-        )
-        .into_compile_error()
-        .into();
+    let (state, direct_initializer): (Type, bool) = match &function.sig.output {
+        ReturnType::Default => (parse_quote!(::iris::android::AndroidUiState), true),
+        ReturnType::Type(_, state) => ((**state).clone(), false),
     };
     if function.sig.inputs.len() != 2
         || function
@@ -46,7 +44,7 @@ pub fn app_init(args: TokenStream, item: TokenStream) -> TokenStream {
     {
         return Error::new(
             function.sig.inputs.span(),
-            "an app_init function takes AndroidUiState and &mut State::Resources",
+            "an app_init function takes UI state and resources",
         )
         .into_compile_error()
         .into();
@@ -64,6 +62,25 @@ pub fn app_init(args: TokenStream, item: TokenStream) -> TokenStream {
         .into();
     }
 
+    let factory = if direct_initializer {
+        quote! {
+            fn init(
+                mut ui_state: ::iris::android::AndroidUiState,
+                rsc: &mut <#state as ::iris::android::AndroidAppState>::Resources,
+            ) -> #state {
+                super::#name(&mut ui_state, rsc);
+                ui_state
+            }
+        }
+    } else {
+        quote! {}
+    };
+    let create = if direct_initializer {
+        quote! { init }
+    } else {
+        quote! { super::#name }
+    };
+
     quote! {
         #[cfg(target_os = "android")]
         #function
@@ -72,12 +89,14 @@ pub fn app_init(args: TokenStream, item: TokenStream) -> TokenStream {
         mod __iris_android_app {
             use super::*;
 
+            #factory
+
             extern "system" fn new_view_peer<'local>(
                 env: ::iris::android::__private::JNIEnv<'local>,
                 view: ::iris::android::__private::View<'local>,
                 context: ::iris::android::__private::Context<'local>,
             ) -> ::iris::android::__private::JLong {
-                ::iris::android::new_peer::<#state>(env, view, context, super::#name)
+                ::iris::android::new_peer::<#state>(env, view, context, #create)
             }
 
             #[unsafe(no_mangle)]