Add import assertions

[Josh-Cena]

Summary

Fixes #14052, fixes #14053, part of mdn/content#19220

First time doing actual compat data changes... I don't really know how this ought to be done. I don't know if this addresses #14053 either.

Test results and supporting details

See https://v8.dev/features/import-assertions

Node versions are hand-tested.

Related issues

[Josh-Cena]

I called it "options" instead of "assertions", because unlike the import statement, the options here permit any unknown attributes from the start, so other keys won't throw parser errors either. In this case, should "assertions" be separately listed as a subfeature to increase discoverability?

[queengooborg]

Thanks! Just a couple of quick updates, and then this will be LGTM!

[queengooborg]

Thanks for the quick fixes!

[Josh-Cena]

"16.14.0" is NOT a valid version number for nodejs

Okay that looks hilarious...

Also, I'm pretty confident it should be called experimental, since we only have V8 support.

[queengooborg]

Experimental set to true sounds good to me!

I've opened up #17367 to add v16.14.0 to the browser data, and will merge that promptly so this PR passes!

[queengooborg]

Ah, we should actually set the second of the three NodeJS statements to partial_implementation, since there are extra details to note regarding compatibility.

By the way, should we create a subfeature for the json assertion type? It might be a little easier to represent the fact that NodeJS added support for the type in 16.15.0 and 17.5.0 (AKA 17.0.0 through 17.4.0 did not have support).

[Josh-Cena]

It's complicated for JSON modules. IIRC it's unflagged in 17.5, but backported to 16.15. I don't think we've reached resolution on what to do in that case—do we? I also don't plan to address #14053 — just focusing on the syntax in this PR. JSON modules would also involve web API I think. (Again it's complicated.)

[queengooborg]

In a case like that, I'd say that we should do the following:

[
  {
    "version_added": "17.5.0"
  },
  {
    "version_added": "16.15.0",
    "version_removed": "17.0.0"
  },
  {
    "version_added": "17.0.0",
    "version_removed": "17.5.0",
    "flags": [
      {
        "type": "runtime_flag",
        "name": "--experimental-json-modules"
      }
    ]
  },
  {
    "version_added": "16.0.0",
    "version_removed": "16.15.0",
    "flags": [
      {
        "type": "runtime_flag",
        "name": "--experimental-json-modules"
      }
    ]
  }
]

It's kind of messy, especially with the flag data, but it's the best we can do with Node's LTS release cycle. WDYT?

[Josh-Cena]

This problem is kind of non-unique—also present in #15123.

Also, do you want to me to do the --experimental-json-modules flag in this PR as well? Frankly I didn't check that. In fact JSON modules and import assertions are two separate things: the latter is merely syntax. I only included a "partial implementation" note about JSON modules in Node for convenience.

[queengooborg]

Yeah, it's an ugly solution, but I feel it is a necessary one due to how NodeJS' release cycle works. On the plus side, doing this allows us to better represent exactly which versions support the feature!

As for the flag, if you're down to incorporate it, that would be great! Otherwise, no big deal; flags quickly become useless to document once they're no longer needed for a feature. ;P

[Josh-Cena]

Sorry @queengooborg I think I'm a bit lost on this. Could you update the PR in the way you want (or in the form of a suggestion) so we can get to merge this?

[hamishwillee]

@queengooborg ^^^ Could you please propose fixes as suggestions to unblock this?

[queengooborg]

I have proposed a solution already, actually -- see #17366 (comment)!

[Josh-Cena]

The flags data for Node is a bit of a mess—there are two flags: --harmony-import-assertions and --experimental-json-modules. The first one enables the parser feature, the second one makes assert { type: "json" } actually "work" (turns on the JSON loader). I don't really know what to do here...

[queengooborg]

I went ahead and pushed the changes I'm looking to see to reduce the back-and-forth and to help get this merged quicker!