fix: return type void in result

macro/src/ret.rs

@@ -6,12 +6,13 @@ use syn::{ReturnType, Type};
 pub(crate) struct ReturnOptions {
 	pub(crate) ty: Option<Box<Type>>,
 	pub(crate) result: bool,
+	pub(crate) void: bool,
 }
 
 impl ReturnOptions {
 	pub(crate) fn parse_signature(ret: &ReturnType) -> Result<Self, syn::Error> {
 		match ret {
-			syn::ReturnType::Default => Ok(Self { ty: None, result: false }),
+			syn::ReturnType::Default => Ok(Self { ty: None, result: false, void: true }),
 			syn::ReturnType::Type(_tok, ty) => match *ty.clone() {
 				syn::Type::Path(path) => {
 					let Some(last) = path.path.segments.last() else {
@@ -25,14 +26,14 @@ impl ReturnOptions {
 							syn::PathArguments::AngleBracketed(ref generics) => for generic in generics.args.iter() {
 								match generic {
 									syn::GenericArgument::Lifetime(_) => continue,
-									syn::GenericArgument::Type(ty) => return Ok(Self { ty: Some(Box::new(ty.clone())), result: true }),
+									syn::GenericArgument::Type(ty) => return Ok(Self { ty: Some(Box::new(ty.clone())), result: true, void: is_void(ty) }),
 									_ => return Err(syn::Error::new(Span::call_site(), "unexpected type in Result")),
 								}
 							}
 						}
 					}
 
-					Ok(Self { ty: Some(Box::new(Type::Path(path.clone()))), result: false })
+					Ok(Self { ty: Some(Box::new(Type::Path(path.clone()))), result: false, void: false })
 				},
 				_ => Err(syn::Error::new(Span::call_site(), "unsupported return type")),
 			},
@@ -41,8 +42,29 @@ impl ReturnOptions {
 
 	pub(crate) fn tokens(&self) -> TokenStream {
 		match &self.ty { // TODO why do we need to invoke syn::Token! macro ???
-			Some(t) => ReturnType::Type(syn::Token![->](Span::call_site()), t.clone()).to_token_stream(),
+			Some(t) => quote::quote!( -> <#t as jni_toolbox::IntoJava<'local>>::T ),
 			None => ReturnType::Default.to_token_stream(),
 		}
 	}
 }
+
+fn is_void(ty: &syn::Type) -> bool {
+	match ty {
+		Type::Array(_) => false,
+		Type::BareFn(_) => false,
+		Type::Group(g) => is_void(&g.elem),
+		Type::ImplTrait(_) => false,
+		Type::Infer(_) => false,
+		Type::Macro(_) => false,
+		Type::Never(_) => true,
+		Type::Paren(p) => is_void(&p.elem),
+		Type::Path(p) => p.path.segments.is_empty(),
+		Type::Ptr(_) => false,
+		Type::Reference(_) => false,
+		Type::Slice(_) => false,
+		Type::TraitObject(_) => false,
+		Type::Tuple(x) => x.elems.is_empty(),
+		Type::Verbatim(_) => false,
+		_ => todo!(),
+	}
+}

macro/src/wrapper.rs

@@ -13,7 +13,7 @@ pub(crate) fn generate_jni_wrapper(attrs: TokenStream, input: TokenStream) -> Re
 
 	let attrs = AttrsOptions::parse_attr(attrs)?;
 	let ret = ReturnOptions::parse_signature(&fn_item.sig.output)?;
-	let return_expr = if ret.ty.is_none() {
+	let return_expr = if ret.void {
 		quote::quote!( () )
 	} else if attrs.return_pointer {
 		quote::quote!( std::ptr::null_mut() )
@@ -49,7 +49,7 @@ pub(crate) fn generate_jni_wrapper(attrs: TokenStream, input: TokenStream) -> Re
 			// V----------------------------------V
 			quote::quote! {
 				{
-					use jni_toolbox::{JniToolboxError, FromJava};
+					use jni_toolbox::{JniToolboxError, FromJava, IntoJava};
 					#transforming
 					match #fn_name_inner(#forwarding) {
 						Ok(ret) => ret,
@@ -65,7 +65,7 @@ pub(crate) fn generate_jni_wrapper(attrs: TokenStream, input: TokenStream) -> Re
 			// V----------------------------------V
 			quote::quote! {
 				{
-					use jni_toolbox::{JniToolboxError, FromJava};
+					use jni_toolbox::{JniToolboxError, FromJava, IntoJava};
 					// NOTE: this should be SAFE! the cloned env reference lives less than the actual one, we just lack a
 					//       way to get it back from the called function and thus resort to unsafe cloning
 					let mut env_copy = unsafe { #env_ident.unsafe_clone() };
@@ -84,7 +84,14 @@ pub(crate) fn generate_jni_wrapper(attrs: TokenStream, input: TokenStream) -> Re
 								},
 							},
 						}
-						Ok(ret) => ret,
+						Ok(ret) => match ret.into_java(&mut env_copy) {
+							Ok(fin) => return fin,
+							Err(e) => {
+								// TODO should we panic instead?
+								let _ = env_copy.throw_new("java/lang/RuntimeException", format!("{e:?}"));
+								return #return_expr;
+							}
+						},
 					}
 				}
 			}
@@ -93,9 +100,16 @@ pub(crate) fn generate_jni_wrapper(attrs: TokenStream, input: TokenStream) -> Re
 		// V----------------------------------V
 		quote::quote! {
 			{
-				use jni_toolbox::{JniToolboxError, FromJava};
+				use jni_toolbox::{JniToolboxError, FromJava, IntoJava};
 				#transforming
-				#fn_name_inner(#forwarding)
+				match #fn_name_inner(#forwarding).into_java(&mut #env_ident) {
+					Ok(res) => return res,
+					Err(e) => {
+						// TODO should we panic instead?
+						let _ = #env_ident.throw_new("java/lang/RuntimeException", format!("{e:?}"));
+						return #return_expr;
+					},
+				}
 			}
 		}
 		// ^----------------------------------^