add core.capture_output

src/logic/scripting/lua/libs/libcore.cpp

@@ -273,6 +273,33 @@ static int l_blank(lua::State*) {
     return 0;
 }
 
+static int l_capture_output(lua::State* L) {
+    int argc = lua::gettop(L) - 1;
+    if (!lua::isfunction(L, 1)) {
+        throw std::runtime_error("function expected as argument 1");
+    }
+    for (int i = 0; i < argc; i++) {
+        lua::pushvalue(L, i + 2);
+    }
+    lua::pushvalue(L, 1);
+
+    auto prev_output = output_stream;
+    auto prev_error = error_stream;
+
+    std::stringstream captured_output;
+
+    output_stream = &captured_output;
+    error_stream = &captured_output;
+    
+    lua::call_nothrow(L, argc, 0);
+
+    output_stream = prev_output;
+    error_stream = prev_error;
+    
+    lua::pushstring(L, captured_output.str());
+    return 1;
+}
+
 const luaL_Reg corelib[] = {
     {"blank", lua::wrap<l_blank>},
     {"get_version", lua::wrap<l_get_version>},
@@ -292,6 +319,7 @@ const luaL_Reg corelib[] = {
     {"get_setting_info", lua::wrap<l_get_setting_info>},
     {"open_folder", lua::wrap<l_open_folder>},
     {"quit", lua::wrap<l_quit>},
+    {"capture_output", lua::wrap<l_capture_output>},
     {"__load_texture", lua::wrap<l_load_texture>},
     {NULL, NULL}
 };