[fs] Add a fs.opensync function to the k6/experimental/fs module

[oleiade]

What?

This Pull Request adds an fs.openSync function to the k6/experimental/fs module, as per #3143.

It allows to open a file as such:

const f = fs.openSync('myfile.txt')

As opposed to the current workaround necessary to go around the limitation of not being able to use await in the init context:

let file
(() => {
  await file = await fs.open('myfile.txt')
)();

Why?

This function acts as a workaround for the lack of support for the await keyword in the init context and is meant to go away as soon as we do. It aims at ensuring a good UX that's more intuitive than the existing workaround ☝🏻

We should document it as such and make it explicit that it won't be supported any further once we address the core issue and that the following syntax is possible:

let f = await fs.open('myfile.txt')

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make ci-like-lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

closes #3143

[codecov-commenter]

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Additional details and impacted files

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[codebien]

We should document it as such and make it explicit that it won't be supported any further once we address the core issue and that the following syntax is possible

I'm not very happy with it. We are adding something that in a cycle could be removed.

If it is useful a lot of people will use it then removing it will make them a lot unhappy.
If it isn't useful then we could just not add.

I would wait for one more cycle before adding it to see the evolution around JS ES modules.

[olegbespalov]

I'm sharing concerns with @codebien regarding adding something temporary.

On the other side, it's an experimental module, and by our definition, the API isn't stable, so it's OK to have this for a few releases.

[oleiade]

There seems to be a consensus that we should not add openSync if we know we won't need it in the foreseeable future.

I'm happy to oblige and will close this Pull Request as a result 🙇🏻

I would consider support for await in the init stage a must-have for taking the fs module out of experimental though, and will add that condition to the issue 👍🏻