Add support for template literals in enums

[IllusionMH]

Fixes #30962

[IllusionMH]

One small question:
If this one is accepted do I need to update Handbook - Enums section?
It has line "a literal enum expression (basically a string literal or a numeric literal)". Should it include somethins like "basically a string literal, a numeric literal, or a template literal without placeholders" or it is unnecessary detail/incorrect statement?

[RyanCavanaugh]

@ahejlsberg just wanted to get a 👍 from you on this one before proceeding

[ahejlsberg]

You made this comment in the issue:

NoSubstitutionTemplateLiteral should be as good as StringLiteral anywhere here IMO

I agree, but this PR narrowly handles string literals in enum initializers. There are multiple other places in the checker where we look for StringLiteral but not NoSubstitutionTemplateLiteral. It's my opinion we should do all of them or none of them.

[weswigham]

It's my opinion we should do all of them or none of them.

Except ES6 imports. Because per spec they aren't allowed there. :(

[IllusionMH]

Oh, I was working in scope of initial issue so this PR only supports enums.
If there are no objections - I will prepare new PR to cover other places and replace this PR.

Just to clarify scope of expected PR:

1. Updates only to checker

2. Add support for NoSubstitutionTemplateLiteral where StringLiteral is supported

3. Do not add TemplateExpressions at this point

4. Exceptions:

   ES6 imports. Because per spec they aren't allowed there.

   Which is already "String literal expected." error.

Is it correct?

[IllusionMH]

I'm finishing my investigation of places where support for NoSubstitutionTemplateLiteral can be added.
Should I create separate issue with list of changes for discussion or draft PR with detailed description would be enough?

[arcanis]

Is there a blocker on this issue I could help with?

[IllusionMH]

I've prepared list of places that have different behavior for template literals and regular strings.
Hope that scope described in #31548 will be approved and I'll send new PR (will include this changes too) this week.

[IllusionMH]

Closing this one in favor of #32064