Backport default empty arguments array

Author: ashtonmeuser

README.md

@@ -55,7 +55,7 @@ See the [Usage wiki page](https://github.com/ashtonmeuser/godot-wasm/wiki/Gettin
 
 1. A small subset of [WASI](https://wasmbyexample.dev/examples/wasi-introduction/wasi-introduction.all.en-us.html) bindings are provided to the Wasm module by default. These can be overridden by the imports supplied on module instantiation. The guest Wasm module has no access to the host machines filesystem, etc. Pros for this are simplicity and increased security. Cons include more work required to run Wasm modules created in ways that require a larger set of WASI bindings e.g. [TinyGo](https://tinygo.org/docs/guides/webassembly/) (see relevant [issue](https://github.com/tinygo-org/tinygo/issues/3068)).
 1. Only `int` and `float` return values are supported. While workarounds could be used, this limitation is because the only [concrete types supported by Wasm](https://webassembly.github.io/spec/core/syntax/types.html#number-types) are integers and floating point.
-1. A default empty `args` parameter for `function(name, args)` can not be supplied. Default `Array` parameters in GDNative seem to retain values between calls. Calling methods of this addon without expected arguments produces undefined behaviour. This is reliant on [godotengine/godot-cpp#209](https://github.com/godotengine/godot-cpp/issues/209).
+1. Default empty `args` parameter for `function(name, args)` is not supported in Godot 3.x using Godot Wasm as an addon e.g. via the Godot Asset Library. Default `Array` parameters in GDNative seem to retain values between calls. Calling methods of this addon without expected arguments produces undefined behaviour. Default empty arguments *are* supported in Godot 4.x and Godot 3.x when using Godot Wasm as a module.
 1. Web/HTML5 export is not supported (see [#15](https://github.com/ashtonmeuser/godot-wasm/issues/15) and [#18](https://github.com/ashtonmeuser/godot-wasm/issues/18)).
 
 ## Relevant Discussion

examples/wasm-test/TestGeneral.gd

@@ -52,6 +52,7 @@ func test_function():
 	var wasm = load_wasm("simple")
 	var result = wasm.function("add", [1, 2])
 	expect_eq(result, 3)
+	expect_empty()
 
 func test_invalid_function():
 	var wasm = load_wasm("simple")
@@ -81,6 +82,17 @@ func test_invalid_function_arg_count():
 	expect_eq(result, null)
 	expect_error("Incorrect number of arguments supplied")
 
+func test_function_default_args():
+	if !Utils.godot_4(): return # Default arguments are unsupported in GDNative
+	var wasm = load_wasm("simple")
+	var result = wasm.function("count") # Expects no arguments
+	expect_eq(result, 1)
+	result = wasm.function("add", [1, 2])
+	expect_eq(result, 3)
+	result = wasm.function("add") # Expects arguments
+	expect_eq(result, null)
+	expect_error("Incorrect number of arguments supplied")
+
 func test_global():
 	var wasm = load_wasm("simple")
 	var global_const = wasm.global("global_const")
@@ -122,8 +134,9 @@ func test_inspect():
 		},
 		"export_functions": {
 			"_initialize": [[], []],
-			"add": [[TYPE_INT, TYPE_INT], [TYPE_INT]]
+			"add": [[TYPE_INT, TYPE_INT], [TYPE_INT]],
+			"count": [[], [TYPE_INT]],
 		},
-		"memory": {}
+		"memory": {},
 	}
 	expect_eq(inspect, expected)

examples/wasm-test/TestMemory.gd

@@ -14,9 +14,10 @@ func test_inspect_compiled():
 		},
 		"export_functions": {
 			"_initialize": [[], []],
-			"add": [[TYPE_INT, TYPE_INT], [TYPE_INT]]
+			"add": [[TYPE_INT, TYPE_INT], [TYPE_INT]],
+			"count": [[], [TYPE_INT]],
 		},
-		"memory": {}
+		"memory": {},
 	}
 	expect_eq(inspect, expected)
 

examples/wasm-test/utils/Utils.gd

@@ -15,3 +15,6 @@ static func file_length(f: File) -> int:
 
 static func to_utf8(s: String) -> PoolByteArray:
 	return s.to_utf8()
+
+static func godot_4() -> bool:
+	return Engine.get_version_info()["major"] == 4

examples/wasm-test/wasm/simple.wasm

@@ -230,7 +230,7 @@ namespace godot {
       ClassDB::bind_method(D_METHOD("load", "bytecode", "import_map"), &Wasm::load);
       ClassDB::bind_method(D_METHOD("inspect"), &Wasm::inspect);
       ClassDB::bind_method(D_METHOD("global", "name"), &Wasm::global);
-      ClassDB::bind_method(D_METHOD("function", "name", "args"), &Wasm::function);
+      ClassDB::bind_method(D_METHOD("function", "name", "args"), &Wasm::function, DEFVAL(Array()));
       ClassDB::bind_method(D_METHOD("set_permissions"), &Wasm::set_permissions);
       ClassDB::bind_method(D_METHOD("get_permissions"), &Wasm::get_permissions);
       ClassDB::bind_method(D_METHOD("has_permission", "permission"), &Wasm::has_permission);