Add support for typeof symbol === "symbol"

[jamiebuilds]

Fixes #2241

[caitp]

I think you're going to need to add another assertion to the tests that use that fixture, but otherwise it looks p. good. Will merge when tests are fixed

[caitp]

actually, I guess you probably won't need to add an assertion, since it's testing that an error isn't thrown... I guess it's okay :>

[jamiebuilds]

It does error if I remove the fix

[caitp]

yeah it's fine, we might want to do a followup to support the new futurehostile feature with it, which would call for some assertions --- but I think this is fine for now

[jamiebuilds]

to support the new futurehostile feature with it,

I'm not sure I understand what that'd consist of.

[caitp]

I'm not sure I understand what that'd consist of.

It just means making it a bit more complicated so that people authoring for ES3/5 environments can keep new features out of their code

[jamiebuilds]

Should it selectively add "symbol" to the typeof list when this option is enabled?

[caitp]

something like that, I'm not sure exactly. @jugglinmike is the expert on it, but it's probably something we can hold back on until someone complains

[jugglinmike]

I don't think the follow-up should use futurehostile because that option is intended to help people avoid authoring code that is difficult to upgrade to future versions of the language. This feature doesn't raise any future portability concerns; in this case, we just want to continue warning about "symbol" in pre-ES6 environments.

Doing this will require additional abstraction around the values array to key off the configured language version.