fix!: Expression.Return.get_value can be null (#149)

* fix!: Expression.Return.get_value can be null

* Add test

src/binaryen_stubs_expressions.c

@@ -1534,7 +1534,12 @@ CAMLprim value
 caml_binaryen_return_get_value(value _exp) {
   CAMLparam1(_exp);
   BinaryenExpressionRef exp = BinaryenExpressionRef_val(_exp);
-  CAMLreturn(alloc_BinaryenExpressionRef(BinaryenReturnGetValue(exp)));
+  BinaryenExpressionRef val = BinaryenReturnGetValue(exp);
+  if (val == NULL) {
+    CAMLreturn(Val_none);
+  } else {
+    CAMLreturn(caml_alloc_some(alloc_BinaryenExpressionRef(val)));
+  }
 }
 
 CAMLprim value

src/binaryen_stubs_expressions.js

@@ -1273,8 +1273,9 @@ function caml_binaryen_drop_set_value(exp, value) {
 
 //Provides: caml_binaryen_return_get_value
 //Requires: binaryen
+//Requires: to_option
 function caml_binaryen_return_get_value(exp) {
-  return binaryen.Return.getValue(exp);
+  return to_option(binaryen.Return.getValue(exp));
 }
 
 //Provides: caml_binaryen_return_set_value

src/expression.ml

@@ -693,7 +693,7 @@ end
 
 module Return = struct
   external make : Module.t -> t -> t = "caml_binaryen_return"
-  external get_value : t -> t = "caml_binaryen_return_get_value"
+  external get_value : t -> t option = "caml_binaryen_return_get_value"
   external set_value : t -> t -> unit = "caml_binaryen_return_set_value"
 end
 

src/expression.mli

@@ -241,7 +241,7 @@ end
 
 module Return : sig
   val make : Module.t -> t -> t
-  val get_value : t -> t
+  val get_value : t -> t option
   val set_value : t -> t -> unit
 end
 

test/test.ml

@@ -20,6 +20,20 @@ let _ = Settings.set_low_memory_unused false
 let wasm_mod = Module.create ()
 let _ = Module.set_features wasm_mod [ Module.Feature.all ]
 
+(* Testing Return.get_value *)
+let _ =
+  assert (
+    Option.is_some
+      (Expression.Return.get_value
+         (Expression.Return.make wasm_mod
+            (Expression.Const.make wasm_mod (Literal.int32 0l)))))
+
+let _ =
+  assert (
+    Option.is_none
+      (Expression.Return.get_value
+         (Expression.Return.make wasm_mod (Expression.Null.make ()))))
+
 (* Create function type for i32 (i32, i32) *)
 let params () = Type.create [| Type.int32; Type.int32 |]
 let results = Type.int32