It looks like you've sent a pull request to update our 'lib' files. These files aren't meant to be edited by hand, as they consist of last-known good states of the compiler and are generated from 'src'. Unless this is necessary, consider closing the pull request and sending a separate PR to update 'src'.

cc @orta

ping @orta :)

ping @DanielRosenwasser

Overall looks good, I think UnicodeBCP47LocaleIdentifier should probably live here and get removed from the 2020 version.

Hmm, is that a breaking change?

That's what I thought but I'm cargo culting and tests seem upset if I just modified src

@DanielRosenwasser what do you think? Should we go ahead and merge this? Seems like the only outstanding question is whether to check in the lib/ changes.

can I get a verdict here 😄 ? cc @DanielRosenwasser @sandersn

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

OK, I've rebased this and set it up locally - as it is a project targeting es2020 would get duplicate identifiers for UnicodeBCP47LocaleIdentifier:

❯ node ../../typescript-compiler/built/local/tsc.js
../../typescript-compiler/built/local/lib.es2016.intl.d.ts:29:10 - error TS2300: Duplicate identifier 'UnicodeBCP47LocaleIdentifier'.

29     type UnicodeBCP47LocaleIdentifier = string;
            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  ../../typescript-compiler/built/local/lib.es2020.intl.d.ts:29:10
    29     type UnicodeBCP47LocaleIdentifier = string;
                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    'UnicodeBCP47LocaleIdentifier' was also declared here.

../../typescript-compiler/built/local/lib.es2020.intl.d.ts:29:10 - error TS2300: Duplicate identifier 'UnicodeBCP47LocaleIdentifier'.

29     type UnicodeBCP47LocaleIdentifier = string;
            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  ../../typescript-compiler/built/local/lib.es2016.intl.d.ts:29:10
    29     type UnicodeBCP47LocaleIdentifier = string;
                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    'UnicodeBCP47LocaleIdentifier' was also declared here.


Found 2 errors.

I think we'll need to remove the identifier from es2020 to have it be usable in es2016. The question of whether this is a breaking change is a good one. If you had a setup like:

"target": "es2019",
"lib": ["es2020.intl"]

and were referring to UnicodeBCP47LocaleIdentifier you would still have access to it because of the target. However, if your target was es2015, and you explicitly just referenced the es2020.intl in lib:

"target": "es2015",
"lib": ["es2020.intl"]

Then moving the type back is a breaking change. Which given the breadth of the TS userbase, someone probably has this setup.

Which gives three options:

• Accept the potential break in the types for target es2015 + a direct reference in lib, and move the identifier to es2016
• NOOP on this change
• Switch the type in es2016 to be string instead of the named alias, keeping UnicodeBCP47LocaleIdentifier in es2020

Personally, I fall into the last bucket.

I personally would pick the 1st option. ECMA402 doesn't often introduce a lot of new APIs per release and have them work independently without previous version, e.g you should not be able specify es2020.intl without es2019.intl and expect it to properly work. Future versions add new options to existing set of limited APIs and normative changes are made to previous types.
UnicodeBCP47LocaleIdentifier is an example of that, it used to just be BCP47 which includes grandfathered locales but was removed in later versions (see tc39/proposal-intl-locale#63 for discussion).
I think the real change (outside of this PR) is probably to make es2020.intl includes all es2015.intl through out es2019.intl.

OK, I think this is good to go now:

• I've removed all the lib references, those changes will get propagated when we update the lkg
• I've removed the es2020.intl reference to UnicodeBCP47LocaleIdentifier. It's now available in es2016.

This last one needs to get mentioned in the 4.5 release notes breaking changes section. Something like:

If you relied on UnicodeBCP47LocaleIdentifier from es2020.intl it is now available in es2016.intl.

I agree it's pretty niche, but a single sentence should be enough to handle covering all cases during migration.

@typescript-bot user test this

Heya @orta, I've started to run the parallelized community code test suite on this PR at b840e5c. You can monitor the build here.

The user suite test run you requested has finished and failed. I've opened a PR with the baseline diff from master.

This PR was deprecated and merged into main via #45647 - thanks @longlho !

This PR was deprecated and merged into main via #45647

I don't see this code anywhere in #45647 or anywhere else in TS (as mentioned elsewhere). Is that intentional?