Backtick literals in enumerations

[arcanis]

TypeScript Version: 3.4.3

Search Terms: backticks / literals / enums

Code

enum Foo {
  hello = `foo`,
};

Expected behavior:

It should work.

This is especially important because the backticks mode of the quotes rule from ESLint breaks programs (cf yarnpkg/berry#70 for an example). While it could be seen as an ESLint bug, I think it should be possible for TS to use raw template string interchangeably with regular strings as long as they don't contain variables.

Actual behavior:

It throws an error (type "foo" is not assignable to type 'Foo').

Playground Link:

https://www.typescriptlang.org/play/index.html#src=enum%20Foo%20%7B%0D%0A%20%20%20%20%20%20%20%20hello%20%3D%20%60foo%60%2C%0D%0A%7D%3B%0D%0A

Related Issues:

I think fixing this should have been part of #21476, but it focused on the case of "a" + "b" rather than the simpler case of a literal without variables.

[RyanCavanaugh]

Would take a PR for it - should be fairly easy

[arcanis]

I'll take a look end at the end of May unless someone beats me to it 🙂

[IllusionMH]

Any objections if I take a try on this issue during this week?

Do I understand correctly that only NoSubstitutionTemplateLiteral should be added to the list of allowed literals?
Should it support concatenations like `backtic` + `backtic` and `backtic` + 'single' ?

[arcanis]

No objection from my side! In my use case the simple literal would be enough, but I guess that given the initial context of #21476 concatenations would be useful too.

[RyanCavanaugh]

NoSubstitutionTemplateLiteral should be as good as StringLiteral anywhere here IMO