Equality (==) does not work properly inflight

[garysassano]

I tried this:

app.w

let j = Json { hello: 123, world: [1, 2, 3] };
assert(Json.values(j) == [Json 123, Json [1, 2, 3]]);

test "inflight" {
  let j = Json { hello: 123, world: [1, 2, 3] };
  assert(Json.values(j) == [Json 123, Json [1, 2, 3]]);
}

I run this command:

wing test app.w

This happened:

The preflight code assertion passes, but the inflight assertion fails:

fail ┌ main.wsim » root/env0/test:inflight
     │ runtime error: assertion failed: Json.values(j) == [Json 123, Json [1, 2, 3]]
     │    --> ../../.volta/tools/image/packages/winglang/lib/node_modules/winglang/node_modules/@winglang/sdk/src/helpers.ts:27:11
     │    | 
     │    | export function assert(condition: any, message: string): asserts condition {
     │    |   if (!condition) {
     │ 27 |     throw new Error("assertion failed: " + message);
     │    |           ^
     │ at assert (/Users/chrisr/.volta/tools/image/packages/winglang/lib/node_modules/winglang/node_modules/@winglang/sdk/src/helpers.ts:27:11)
     │ at handle (/Users/chrisr/dev/wing-test/main.w:6:3)
     │ at handler (/Users/chrisr/dev/wing-test/target/test/main.wsim/.wing/handler_c8054fcc.js:17:25)
     └ at processTicksAndRejections (node:internal/process/task_queues:95:5)

I expected this:

I expected Wing assertion to work, because the compiled JS code doesn't throw any error when pasted into Node.js REPL.

preflight.js

const j = ({"hello": 123,"world": [1, 2, 3]});
{((cond) => {if (!cond) throw new Error("assertion failed: Json.values(j) == [Json 123, Json [1, 2, 3]]")})((((a,b) => { try { return require('assert').deepStrictEqual(a,b) === undefined; } catch { return false; } })((Object.values(j)),[123, [1, 2, 3]])))};

Is there a workaround?

No response

Component

Compiler

Wing Version

No response

Node.js Version

No response

Platform(s)

No response

Anything else?

No response

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[garysassano]

Found about this with @hasanaburayyan while doing some tests.

[ekeren]

@Chriscbr FYI

[Chriscbr]

It appears to be an issue with how Object.values and equality behave in a VM:

let code = `
const j = {};
const values = Object.values(j);
const expected = [];
console.log(Object.getPrototypeOf(values) === Object.getPrototypeOf(expected));
console.log({}.constructor.prototype === Object.prototype);
require('assert').deepStrictEqual(values, expected);
console.log("done");
`
eval(code);

let vm = require("vm").runInNewContext(code, {
    require,
    Object,
    console,
});
console.log(vm);

error:

node vm.js
true
true
done
false
false
node:assert:124
  throw new AssertionError(obj);
  ^

AssertionError [ERR_ASSERTION]: Values have same structure but are not reference-equal:

[]

    at evalmachine.<anonymous>:7:19
    at Script.runInContext (node:vm:141:12)
    at Script.runInNewContext (node:vm:146:17)
    at Object.runInNewContext (node:vm:300:38)
    at Object.<anonymous> (/Users/chrisr/dev/wing-test/vm.js:12:24)
    at Module._compile (node:internal/modules/cjs/loader:1254:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1308:10)
    at Module.load (node:internal/modules/cjs/loader:1117:32)
    at Module._load (node:internal/modules/cjs/loader:958:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12) {
  generatedMessage: true,
  code: 'ERR_ASSERTION',
  actual: [],
  expected: [],
  operator: 'deepStrictEqual'
}

[ekeren]

I don't think it ever worked

[Chriscbr]

I updated the example in my code above -- it's quite interesting that {}.constructor.prototype === Object.prototype works outside of the VM but not inside it.

In either case, I seems assert.deepStrictEqual is doing a little bit more work than we need it to (according to the NodeJS docs it compares the prototypes of objects -- but I don't think this check needed for our language's equality semantics).

What if we compile a == b into something like $stdlib._equals(a, b), and define our own custom equality logic in the SDK?

[hasanaburayyan]

@Chriscbr freaking dope catch, I did not think about testing this in a vm. I was pretty baffled at why the hell there was a difference.

[staycoolcall911]

I think @Chriscbr's solution makes sense - we should implement our own equality logic instead of the current solution, which uses deepStrictEqual.

[Chriscbr]

It looks like the code shared in the original post works since we're executing preflight code inside of a worker thread - but the assertion still fails for inflight code:

test "inflight" {
  let j = Json { hello: 123, world: [1, 2, 3] };
  assert(Json.values(j) == [Json 123, Json [1, 2, 3]]);
}

I've updated the issue title to reflect this.

[MarkMcCulloh]

See #4725, which I think would be an ideal solution for this issue

[monadabot]

Congrats! 🚀 This was released in Wing 0.59.43.