Fails to parse Flow-annotated polymorphic methods which name is a keyword

[danez]

I started using Flow recently, and was delighted to see that Babel (which I was already using) supported stripping Flow types by default already! I just found a funny issue though:

sebmck: It's being parsed as a JSX tag for some reason.
sebmck: Figured it out exprAllowed is being set to true on delete tokens so the < is being interpreted as the start of a JSX starting tag expression.
thejameskyle: @sebmck is this an easy one to tackle?

class Foo {
  delete<T>(item: T): T {
    return item;
  }
}

copied from https://phabricator.babeljs.io/T1737

[danez]

I tried to solve this some months ago, but couldn't figure out how to fix. This not only happens for delete but also for some other keywords, can't remember which. Maybe void.

[danez]

declare class A {
   while<T>(): void; // this parses
   do<T>(): void; // this does not
}

The input code should parse, however it errors at the '<' after the 'do'.

The above fails to parse because the 'do' keyword is marked as {beforeExpr: true} in tokenizer/types.js.
Then tokenizer interprets the '<' after the do as the start of a jsx tag, rather than as a relational '<'.

The 'while' variant works because it is not marked beforeExpr.

The above will repro with any method whose name is a keyword marked with beforeExpr true, which are:
case, default, do, else, return, throw, new, extends, yield, in, instanceof, typeof, void, delete.

https://phabricator.babeljs.io/T7284

[vkurchatkin]

The same for get/set

[vkurchatkin]

Fixed the get/set part: #55

[vkurchatkin]

@danez it seems that your examples work on master

[danez]

No both are not working yet.

[vkurchatkin]

Hmm, they work for me. Do you have jsx plugin enabled?

[danez]

yes

declare class A {
   while<T>(): void; // this parses
   do<T>(): void; // this does not
}

{
  "sourceType": "module",
  "plugins": ["jsx", "flow", "asyncFunctions"]
}

Unexpected token (3:2)

[danharper]

I've got a WIP of a fix for this. I think there's still some edge cases to cover to match Flow though (or, they might be bugs in Flow..) I'll probably have a PR ready this weekend.