Support Flow Enums

[lyleunderwood]

Babel added support for flow enums here: babel/babel#10344

Currently trying to import an enum results in MyEnum not found in enum-module

They're currently experimental, but should be coming down the pipe. I think it would be pretty trivial to support these, basically add an EnumDeclaration everywhere there is currently a TSEnumDeclaration.

I tried working on a PR for this, but the problem is getting the tests running. EnumDeclaration was added in babel 7.7.0. I was trying to get @babel/eslint-parser going in all the flow-related tests while retaining babel-eslint in other tests, but I kept running into problems.

[Brianzchen]

Flow Enums have shipped and at first usage import/named throws an error.

import { MyEnum } from 'enumModule'; // errors
MyEnum.A; // Ideal usage

import * as EnumModule from 'enumModule';
EnumModule.MyEnum.A; // Not so ideal but no errors this way

[ljharb]

That’s expected, when the issue asking to support them remains open :-)

[ljharb]

We have better testing around specific parsers now than we did back in May, so it may be easier to attempt a PR now.

[Brianzchen]

@ljharb I've have a look into this one now and just working on getting tests to run and noticed that babel-core is version 6.26.3 but to support transpiling enums the docs need >=7.13.0. Any thoughts here?

Also side note I'll need to add a babel plugin to interact with the RuleTester would you expect that to be added here?

[ljharb]

In that case we’ll need a bit of infra change to be able to test on both Babel 6 and babel 7.

[Brianzchen]

Should v6 still be supported? It's years old at this point? Just wondering is all.

Also want to add that import/exports also has an issue when there is a module that contains only an enum type, it will throw saying No named exports found in module ...

[ljharb]

Yes, we still support down to eslint 2. Age is irrelevant.

I’m in the process of updating this package to more easily test across multiple parsers, including Babel 7. I’ll comment here once that’s done.

[chrisbobbe]

I was trying to get @babel/eslint-parser going[…]

Can @babel/eslint-parser actually work with Flow enums? The Flow doc is pretty vague; I think its claim is just (quote) "this may also work".

With that as my chosen parser in my eslintrc, I got an ESLint error with

Parsing error: Unexpected token, expected "{"

on a Flow enum definition. When I changed the parser to hermes-eslint (npm, GitHub; the one the Flow doc seems to promote most), the error went away. A quote from hermes-eslint's README: "It is the recommended parser for use for linting with Flow code."

In any case, this seems like a very helpful next step:

I’m in the process of updating this package to more easily test across multiple parsers