ucode-mod-lua: support prototype lookups and method calls on ucode values

Expose ucode arrays and objects with prototypes as userdata proxy objects
to Lua and extend the userdata metadatable with an __index metamethod to
lookup not found properties in the ucode values prototype chain.

Also extend the __call metamethod implementation to infer method call
status from the activation record in order to invoke ucode functions with
the correct `this` context when called as method from Lua.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

contrib/package/ucode-mod-lua/src/lua.c

@@ -155,6 +155,21 @@ ucv_to_lua(uc_vm_t *vm, uc_value_t *uv, lua_State *L, struct lh_table *visited)
 
 	case UC_ARRAY:
 	case UC_OBJECT:
+		if (ucv_prototype_get(uv)) {
+			ud = lua_newuserdata(L, sizeof(*ud));
+
+			if (ud) {
+				ud->vm = vm;
+				ud->uv = ucv_get(uv);
+
+				luaL_getmetatable(L, "ucode.value");
+				lua_setmetatable(L, -2);
+			}
+			else {
+				lua_pushnil(L);
+			}
+		}
+		else {
 			if (!visited) {
 				freetbl = true;
 				visited = lh_kptr_table_new(16, NULL);
@@ -180,6 +195,7 @@ ucv_to_lua(uc_vm_t *vm, uc_value_t *uv, lua_State *L, struct lh_table *visited)
 			else {
 				lua_pushnil(L);
 			}
+		}
 
 		break;
 
@@ -401,17 +417,28 @@ lua_uv_call(lua_State *L)
 	ucv_userdata_t *ud = luaL_checkudata(L, 1, "ucode.value");
 	int nargs = lua_gettop(L), i;
 	uc_value_t *rv;
+	lua_Debug ar;
+	bool mcall;
 
 	if (!ucv_is_callable(ud->uv))
 		return luaL_error(L, "%s: Invoked value is not a function",
 			uc_exception_type_name(EXCEPTION_TYPE));
 
+	if (!lua_getstack(L, 0, &ar) || !lua_getinfo(L, "n", &ar))
+		return luaL_error(L, "%s: Unable to obtain stackframe information",
+			uc_exception_type_name(EXCEPTION_RUNTIME));
+
+	mcall = !strcmp(ar.namewhat, "method");
+
+	if (mcall)
+		uc_vm_stack_push(ud->vm, lua_to_ucv(L, 2, ud->vm, NULL));
+
 	uc_vm_stack_push(ud->vm, ucv_get(ud->uv));
 
-	for (i = 2; i <= nargs; i++)
+	for (i = 2 + mcall; i <= nargs; i++)
 		uc_vm_stack_push(ud->vm, lua_to_ucv(L, i, ud->vm, NULL));
 
-	if (uc_vm_call(ud->vm, false, nargs - 1)) {
+	if (uc_vm_call(ud->vm, mcall, nargs - 1 - mcall)) {
 		rv = ucv_object_get(ucv_array_get(ud->vm->exception.stacktrace, 0), "context", NULL);
 
 		return luaL_error(L, "%s: %s%s%s",
@@ -428,6 +455,26 @@ lua_uv_call(lua_State *L)
 	return 1;
 }
 
+static int
+lua_uv_index(lua_State *L)
+{
+	ucv_userdata_t *ud = luaL_checkudata(L, 1, "ucode.value");
+	const char *key = luaL_checkstring(L, 2);
+	uc_value_t *proto, *rv;
+	bool found;
+
+	proto = ucv_prototype_get(ud->uv);
+	rv = ucv_object_get(proto, key, &found);
+
+	if (!found)
+		return 0;
+
+	ucv_to_lua(ud->vm, rv, L, NULL);
+	ucv_put(rv);
+
+	return 1;
+}
+
 static int
 lua_uv_tostring(lua_State *L)
 {
@@ -443,6 +490,7 @@ lua_uv_tostring(lua_State *L)
 static const luaL_reg ucode_ud_methods[] = {
 	{ "__gc",			lua_uv_gc         },
 	{ "__call",			lua_uv_call       },
+	{ "__index",		lua_uv_index      },
 	{ "__tostring",		lua_uv_tostring   },
 
 	{ }
@@ -899,8 +947,6 @@ uc_lua_create(uc_vm_t *vm, size_t nargs)
 
 	luaL_newmetatable(L, "ucode.value");
 	luaL_register(L, NULL, ucode_ud_methods);
-	lua_pushvalue(L, -1);
-	lua_setfield(L, -2, "__index");
 	lua_pop(L, 1);
 
 	return uc_resource_new(vm_type, L);