Get NativeFunc passing basic tests

lib/api/tests/module.rs

@@ -156,3 +156,48 @@ fn exports() -> Result<()> {
     );
     Ok(())
 }
+
+#[test]
+fn native_function_works_for_wasm() -> Result<()> {
+    let store = Store::default();
+    let wat = r#"(module
+    (func $multiply (import "env" "multiply") (param i32 i32) (result i32))
+    (func (export "add") (param i32 i32) (result i32)
+       (i32.add (local.get 0)
+                (local.get 1)))
+    (func (export "double_then_add") (param i32 i32) (result i32)
+       (i32.add (call $multiply (local.get 0) (i32.const 2))
+                (call $multiply (local.get 1) (i32.const 2))))
+)"#;
+    let module = Module::new(&store, wat)?;
+
+    let import_object = imports! {
+        "env" => {
+            "multiply" => Function::new(&store, |a: i32, b: i32| a * b),
+        },
+    };
+
+    let instance = Instance::new(&module, &import_object).unwrap();
+
+    // TODO:
+    //let f: NativeFunc<(i32, i32), i32> = instance.exports.get("add").unwrap();
+    let dyn_f: &Function = instance.exports.get("add").unwrap();
+    let dyn_result = dyn_f.call(&[Val::I32(4), Val::I32(6)]).unwrap();
+    assert_eq!(dyn_result[0], Val::I32(10));
+
+    let f: NativeFunc<(i32, i32), i32> = dyn_f.clone().native().unwrap();
+
+    let result = f.call(4, 6).unwrap();
+    assert_eq!(result, 10);
+
+    let dyn_f: &Function = instance.exports.get("double_then_add").unwrap();
+    let dyn_result = dyn_f.call(&[Val::I32(4), Val::I32(6)]).unwrap();
+    assert_eq!(dyn_result[0], Val::I32(20));
+
+    let f: NativeFunc<(i32, i32), i32> = dyn_f.clone().native().unwrap();
+
+    let result = f.call(4, 6).unwrap();
+    assert_eq!(result, 20);
+
+    Ok(())
+}