Default importAttributesKeyword to with

[JLHwung]

Q	A
Fixed Issues?	Fixes #16975
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

In this PR we defaults the Babel 7 generator option importAttributesKeyword (IAK) to with and prints the missing IAK warning only when users are using a non-standard import attributes syntax, e.g. assert { type: "json" } or with type: "json".

Given that the import attributes proposal has reached stage 4, I think such a change should be considered spec compliance: Babel should output valid JS syntax by default and we should not nudge users for the importAttributesKeyword option unless they are actually using the out-dated syntax.

Caveat: it could be a breaking change for users when these conditions are both satisfied:

1. Users depend on a long deprecated import attributes syntax with type: "json"
2. Users have pinned @babel/parser but chooses to update @babel/generator to the latest version

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/58359

[JLHwung]

The attributes-with-to-default is merged with this case now that we output the standard syntax by default.

[JLHwung]

We output the standard syntax on input import "a" with { type: "json" }; and options

{
  "BABEL_8_BREAKING": false,
  "plugins": ["importAssertions"]
}

[JLHwung]

We output the standard syntax on input import "a" assert { type: "json" }; and options

{
  "BABEL_8_BREAKING": true,
  "plugins": ["deprecatedImportAssert"]
}

[JLHwung]

The input is already valid: import "a" with { type: "json" };

[liuxingbaoyu]

1. Users depend on a long deprecated import attributes syntax with type: "json"

From what I understand we already avoid this with extra?

2. Users have pinned @babel/parser but chooses to update @babel/generator to the latest version

Perhaps we could add extra to with instead of with-legacy to avoid this?

[nicolo-ribaudo]

I have a light preference for doing the opposite: for Babel 7, we store on .extra that the user is using the new syntax.

However, it's more out of a purity semver point of view, and I agree that it's very likely that this wouldn't break anybody. https://www.npmjs.com/package/@babel/plugin-syntax-module-attributes has been deprecated for ages, and it has basically no downloads.

[JLHwung]

If we add extra to the standard syntax but later remove it in Babel 8, I think it will unnecessarily confuse plugin developers: Although Babel 8 will not support with-legacy syntax, the feature detection such as if (node.extra.standardWithSyntax) will break in Babel 8 if we do the opposite.

Like Nicolò has mentioned, there is basically no downloads for the long deprecated syntax, I would prefer to promote the ES2025 syntax and hide the IAK option: This option has served its purpose well and it's time to move on.

[nicolo-ribaudo]

Wdyt about doing this in a minor release, so we can at least mention it in the blog post?