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Question on class/method/property location data when it has decorator(s)

JamesHenry opened this issue · comments

commented

I find it a little unintuitive that if you apply a decorator to a method (or other target construct such as a class), the method's location data does not include the decorator, given that the decorators: [] array is a property of the node.

Both the TypeScript and Flow parsers (the only others I believe support decorators) behave differently to Babylon here, their relevant method node location includes the decorator content.

I could not find any guidance on location data within https://github.com/tc39/proposal-decorators

Was this behaviour explicitly discussed and decided on in Babylon? Are there other precedents of nested nodes "overflowing" their parents?

Example Code

class Other {
    @foo({ baz: true })
    static get bar() { return this._bar; }
}

Live example: http://astexplorer.net/#/gist/c7692dd145ef9aaa2c9600f976257a2a/bf55ed4537b7520a6c19045d7e9fa4e6f3f11d14

...take a look at the highlighted method for Bablyon vs TypeScript and Flow (and the location data in the AST of course).

commented

Hey @JamesHenry! We really appreciate you taking the time to report an issue. The collaborators
on this project attempt to help as many people as possible, but we're a limited number of volunteers,
so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack
community that typically always has someone willing to help. You can sign-up here
for an invite.

commented

@JamesHenry IIRC this is fixed in decorators2

commented

Indeed it is, thanks, @existentialism!

Updating my parser config to use decorators2 instead of decorators fixes it, however it clashes quite badly with the TypeScript support, because TS has more options for things like parameter decorators than decorators2 allows (cc @andy-ms)

Is there any reason not to apply the location fix to the decorators plugin as well? That works perfectly with TypeScript as far as I can tell. (I'm happy to submit the PR if it will be accepted)

commented

(Updated the description a bit as this does not just apply to method decorators)

commented

@JamesHenry not sure how others feel re: making changes to old decorator plugin, but I'm fine with it... and nice side effect: it'll help remove some comment-related hacking in prettier as well.

commented

Yep, and I'm sure @vjeux will be happy about that 😄

@hzoo @danez How do you feel about me adding the location fix to the original decorators plugin?

commented

I'd be super happy indeed :p

commented

Go ahead.

commented

Thanks @jridgewell, PR opened here #699

commented

The PR was merged! Thanks all