esm custom loader: multiple calls to nextHook within the same loader result in different nextHooks

[JakobJingleheimer]

Version

pre-release / nightly

Platform

macOS 12.3.1, M1

Subsystem

esm, loaders

What steps will reproduce the bug?

loader-a.mjs

export function resolve(specifier, context, nextHook) {
  assert(nextHook(…) === nextHook(…));
}

How often does it reproduce? Is there a required condition?

100%

A loader hook must call nextHook() more than once to reproduce.

What is the expected behavior?

nextHook should be the same within the same loader

What do you see instead?

The first nextHook is correctly the next in the chain; however, subsequent calls erroneously continue along the hook chain.

Additional information

Thanks @cspotcode for reporting.

Note that this requires loader chaining (#42623), which has not yet been released.

The problem is caused by ESMLoader::resolve() and ESMLoader::load() decrementing hookIndex every time next<HookName> is called. I believe this can be addressed by using a factory to produce the next<HookName> and decrementing the counter in there instead.

[JakobJingleheimer]

My proposed solution above will create a conflict with #43164 (merging soon), so I'll wait til that's merged before sending a PR for this.