ERROR: indexing array with string in Promise.serial()

[gjanvier]

Promise.serial() makes my imp04 device crash.

I found a workaround by reimplementing this function with a tiny variation, but the fact that it solves the issue makes no sense for me. I don't know what I am talking about, but I suspect a bug in the squirel VM itself. So please consider my test case.

I tried to simplify my app, so this sample may seem to be too complex for the features it implements.

RUN on imp04, device or agent.

#require "Promise.lib.nut:4.0.0"

// Here we will test several variations of Promise.serial

function Promise_serial(promises) {
    // static method
    return Promise.serial(promises);
}

function Promise_serial1(promises) {
    // Copy/paste of Promise.serial
    local i = 0;
    return Promise.loop(
        @() i < promises.len(),
        function () {
            return "function" == type(promises[i]) // you'll see that this i integer will become a string??
                 ? promises[i++]()
                 : promises[i++];
        }
    )
}

function Promise_serial2(promises) {
    // Just a tiny change in Promise.serial
    local i = 0;
    return Promise.loop(
        @() i < promises.len(),
        function () {
            // I don't know why but I had to change the order here
            local res = promises[i++];
            if ("function" == type(res)) {
                res = res();
            }
            return res;
        }
    )
}

// My simplified app
// I removed everything that is not required to reproduce the bug

/**
 * Simulates an asynchronous command that is sent to a device throuh a serial interface
 * and its response.
 */
function executeCommand(cmd) {
    server.log("--> " + cmd);
    return Promise(function(resolve, reject) {
        imp.wakeup(0, function() {
            server.log("<-- " + cmd);
            resolve(true);
        });
    });
}


currentCommandPromise <- null;

/**
 * Wrapper that make sure that only one command is running at a time.
 */
function commandWrapper(callback) {
    if (null == currentCommandPromise) {
        currentCommandPromise = callback();
    }
    else {
        currentCommandPromise = currentCommandPromise.then(
            function(value) { // onFulfilled
                return callback();
            },
            function(reason) { // onError
                logger.error("Failed callback: " + reason);
                return callback();
            }
        );
    }

    return currentCommandPromise;
}

/**
 * Callback executed when the device starts
 */
function onStartCallback() {
    local promises = [
        function() {
            return executeCommand("onStartCallback");
        },
        // We would expect more commands here
    ];

    return commandWrapper(function() {
        return Promise.serial(promises);
    });
}


// My tests with the Promise.serial variation


function test() {
    server.log("Run test");
    
    local promises = [
        function() {
            return onStartCallback();
        },
        // We would expect more commands here
    ];

    Promise_serial(promises);
}

function test1() {
    server.log("Run test1");
    
    local promises = [
        function() {
            return onStartCallback();
        },
        // We would expect more commands here
    ];

    Promise_serial1(promises);
}

function test2() {
    server.log("Run test2");
    
    local promises = [
        function() {
            return onStartCallback();
        },
        // We would expect more commands here
    ];

    Promise_serial2(promises);
}


// main
// Pick the test you want
test(); // crash with ERROR: indexing array with string
//test1(); // crash with ERROR: indexing array with string
//test2(); // this test works fine

If you run test() or test1() which runs the same code:

2021-03-22T21:57:01.360 +00:00 | [Agent] | Run test
2021-03-22T21:57:01.374 +00:00 | [Agent] | ERROR: indexing array with string
2021-03-22T21:57:01.374 +00:00 | [Agent] | ERROR:   in commandWrapper agent_code:64
2021-03-22T21:57:01.374 +00:00 | [Agent] | ERROR:   from unknown electricimp#promise.lib.nut#4.0.0:251
2021-03-22T21:57:01.374 +00:00 | [Agent] | ERROR:   from unknown electricimp#promise.lib.nut#4.0.0:219

But if you run test2() it is OK

2021-03-22T21:57:25.095 +00:00 | [Agent] | Run test2
2021-03-22T21:57:25.133 +00:00 | [Agent] | --> onStartCallback
2021-03-22T21:57:25.153 +00:00 | [Agent] | <-- onStartCallback

I let you play with this test2() and try to understand what makes the difference. From my understanding, it is the position of the i++. There is no reason for it, but in the crashing tests, this integer suddenly becomes a string!?!

I've spend quite a lot of time to investigate, don't hesitate to point out any stupid error I made, but please enlighten me ;-)

[pdh11]

Somewhat surprisingly, not in fact a bug, see https://forums.electricimp.com/t/my-integer-suddenly-becomes-a-string/6454

[smittytone]

This will be addressed in 4.0.1