"cannot coerce undefined to object" - Spread into array syntax issues

[lll000111]

EDIT Very small reproducible example added in a comment below.

---

I have a weird problem that running in isolation works just fine.

Code

(Excerpt)

  if (thing.referenceTo !== undefined) {
    trace(thing.referenceTo + '\n');
    for (let entry of thing.referenceTo) {
      trace(entry + '\n');
    }

    [...thing.referenceTo];  // LOCATION OF ERROR, line #178

thing.referenceTo is a Set with a single string value "*" inside as shown by the trace output below.

Output

I wish I could copy & paste from the console in xsbug....

[object Set]
'*'
the-file.js (178) # Break: the-function: cannot coerce undefined to object!

The same thing happens in another place (the case is resched because Object.prototype.toString.call returned string "Set", which was extracted, so obj is sure to be a Set):

case 'Set':
      return actualStringify([...obj], seenObjects);

Just for the record, all of that is well-tested, the exact same code, just a mini-example of our stuff, runs on node.js browser, react-native - and even low.js (on this board).

Works when run in isolation

I tried to run this as an isolated example:

function isString(thing) {
  return typeof thing === 'string';
}

const thing = {
  referenceTo: new Set(['*'])
};

trace(thing.referenceTo + '\n');

for (let entry of thing.referenceTo) {
  trace(entry + '\n');
}

if (
  thing.referenceTo !== undefined &&
  (
    !(thing.referenceTo instanceof Set) ||
    ![...thing.referenceTo].every(type => isString(type))
  )
) {
  throw new Error('Error');
}

but this worked fine.

[lll000111]

PS: I'll keep debugging and if I can't think of anything else create a runnable example to send you.

EDIT: Blocked by #141 in this attempt.

EDIT ²: Unblocked by manifest.json entry `"strip": "[]", but the minimal examples keep working.... :(

[lll000111]

An update: When I replace the [...setObject] by Array.from(setObj) it works. So it seems that there is an issue specifically when the object spread syntax is used. But it only happens in the large project thus far, which I keep shrinking piece by piece to get a small test case. <Sigh>

[lll000111]

Reproducible example

The error is connected to array spread syntax. Everything works if I replace it with Array.from. Also, there have to be two spreads, the first one works.

I ran it on Linux, but I discovered the issue originally on ESP32.

There are two different errors. To discover the first one just uncomment the code marked Error #1.

'use strict';

function isString (thing) {
    return typeof thing === 'string';
}

function ensureRecipeRule (thing) {
    if (thing.referenceTo instanceof Set) {
        [...thing.referenceTo].every(type => isString(type));
    }

    // ERROR #1
    // THE EXACT SAME THING AS ABOVE REPEATED: "callback is no function"
    // if (thing.referenceTo instanceof Set) {
    //     [...thing.referenceTo].every(type => isString(type));
    // }

    // ERROR #2
    // "cannot coerce undefined to object"
    if (thing.idReferenceTo instanceof Set) {
        [...thing.idReferenceTo].every(type => isString(type));
    }
}

trace('Start\n');

[
    {
        referenceTo: new Set(['Person']),
    },
    {
        idReferenceTo: new Set(['Group'])
    }
]
.map(rule => ensureRecipeRule(rule));

trace('End\n');

Result (Error 2):

The "callback is no function" error can also be reproduced simply by

function isString (s) {
    return typeof s === 'string';
}

const s1 = new Set('s1');

[...s1].every(isString);
[...s1].every(isString);  // the 2nd call fails

[lll000111]

Another possibly related example:

Test performed on Linux.

Code

const a1 = [1,2,3];
const a2 = [];

const result = [...a1, ...a2];

Expected Result

[1, 2, 3]

Actual Result

undefined

[phoddie]

This was fixed a while back.