@qwitwa's V8 REPL concern

@avivkeller

@avivkeller Apologies for abusing this PR for an off topic DM, but I would appreciate some guidance in what, if anything, should be done to raise the issue I encountered, and if so, where. I had a look on the chromium issue tracker and found a few similarish discussions but was honestly intimidated by it. In my own app, I've fixed this by stripping the contents of the backticks and only completing on an empty string. That approach works for me and I expect it would work in a statistical majority of cases, but it doesn't seem actually Correct (there's nothing actually preventing an empty template argument to a tag function from side-effecting, never mind the fact that I'm assuming "my" code is handling nesting complexities right with acorn, but it's vibecoded and I haven't reviewed it properly.)

Is this worth filing a node issue for? V8 only? Is there a chat room that would make sense for me to visit to get pointed in the right direction? Feel free to ignore this if you don't have the spoons, since it isn't relevant to this PR as you've said. I just figured whilst I have the motivation for this it might be worth making it bureaucratically visible.

Originally posted by @qwitwa in nodejs/node#64034 (comment)

Can you make a minimal reproduction without relying on external libraries? Here's how to check if a function has side effects:

import { Session } from 'node:inspector/promises';

const session = new Session();
session.connect();

async function hasSideEffects(expression) {
  const { exceptionDetails } = await session.post('Runtime.evaluate', {
    expression,
    throwOnSideEffect: true,
    returnByValue: true,
  });

  if (!exceptionDetails) return false;

  const desc = exceptionDetails.exception?.description ?? exceptionDetails.text ?? '';
  if (/[Pp]ossible side-effect/.test(desc)) return true;
  throw new Error(`evaluation failed: ${desc}`);
}

Actually, I rewrote the completion logic to accomodate those changes, and will update the PR

Sick. I did have a go at compiling your PR but I'm on a steam deck and with make -j2 to avoid running out of ram it's been 2 hours already. The dax pattern is a tag function that returns a side-effectful thennable, so assuming I found a repro, I was going to go look for the details of how await gets handled behind the scenes, but honestly I'm probably out of my depth - ideally I'd have a much more solid and total grasp of semantics nooks and crannies before trying to trace "is this safe to eval" code. .

Wow! Compiling node on a steam deck is certainly not something that happens often. Thank for your help identifying this bug, and I'm so glad my PR fixes yet another wacky quirk of the REPL!

I did end up managing to follow (badly, wish I'd started using ninja) the build/test instructions, and after an age ended up with this; is this expected? I'm sleep deprived right now, I'll have more spoons to take stuff in maybe in a day or two.

Node.js v27.0.0-pre
Command: out/Release/node /home/deck/Code/external/node/test/parallel/test-snapshot-reproducible.js


[14:14|% 100|+ 5726|-   1]: Done

Failed tests:
out/Release/node /home/deck/Code/external/node/test/parallel/test-snapshot-reproducible.js
make[1]: *** [Makefile:322: jstest] Error 1
make: *** [Makefile:359: test-only] Error 2

Full (well, up to what was printed to the console) verbose assertion failure at https://gist.github.com/qwitwa/baf4d4099aa38942af9edd7abda699c0

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@qwitwa's V8 REPL concern #5156

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@qwitwa's V8 REPL concern #5156

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avivkeller commented on Jun 28, 2026

avivkeller commented on Jun 30, 2026

qwitwa commented on Jul 1, 2026

avivkeller commented on Jul 1, 2026

qwitwa commented on Jul 2, 2026

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