Definite assignment assertions not in AST

[azz]

What version of TypeScript are you using?
typescript@2.7.0-dev.20171224

What version of typescript-eslint-parser are you using?
master

What code were you trying to parse?

class X { a!: any }

What did you expect to happen?
Something like definite: true or exclamationToken: true in the AST. In the TS AST it is called exclamationToken.

New in microsoft/TypeScript#20166

What happened?

{
  type: 'ClassProperty',
  range: [ 10, 17 ],
  loc: {...},
  key:  {...},
  value: null,
  computed: false,
  static: false,
  readonly: undefined,
  typeAnnotation:  {...}
}

Thoughts on which property name to go for?

[sgoll]

I'd go with exclamationToken for two reasons:

1. The parser should IMHO add as little additional interpretation (i.e. semantics) as possible, and for now the exclamation mark token might mean "definite" but this may change or broaden at some later point.
2. The TS AST calls it exclamationToken and sticking to the same name avoids confusion.

[JamesHenry]

For me the parallel with optional (coming from questionToken in the original TS AST) is very strong.

As per Nicolo's comment here: babel/babel#7159 (comment)

[JamesHenry]

@sgoll We will definitely be going for whatever is agreed on that babylon PR to stay aligned, so if you feel strongly about it either way please add to the discussion on there. Thanks!

[sgoll]

@JamesHenry Done that, and you are right, of course—the parallel with optional is strong.