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Parser allows spaces between # and identifier #8225

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ramin25 opened this issue Jun 25, 2018 · 6 comments · Fixed by #8756
Closed

Parser allows spaces between # and identifier #8225

ramin25 opened this issue Jun 25, 2018 · 6 comments · Fixed by #8756
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claimed outdated A closed issue/PR that is archived due to age. Recommended to make a new issue pkg: parser Spec: Class Fields

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@ramin25
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ramin25 commented Jun 25, 2018

Bug Report

Current Behavior
First identified in: Class Fields (Stage 3) #12
The parser currently allows spacing between the private name symbol # and the identifier.

However, it seems to violate the lexical grammar in the spec proposal:

PrivateName:: #IdentifierName

Input Code

class Foo {
    #    p = 0;
    constructor() {
        this.#   p   ++;
    }

    print() {
        console.log(this   .   #    p);
    }
}

Expected behavior/code
Babel should communicate the parser error, e.g: "Spaces not permitted in private field name"

Babel Configuration (.babelrc, package.json, cli command)

const presets = [
  ["@babel/env", {
    targets: {
      node: "6"
    },
    useBuiltIns: "usage"
  }]
];

module.exports = { presets,
    "plugins": ["@babel/plugin-proposal-class-properties"]
 };

Environment

  • Babel version(s): [v7.0.0-beta.34]
  • Node/npm version: [e.g. Node 6/npm 3.10.10]
  • OS: [Windows 7]
  • Monorepo [no]
  • How you are using Babel: [cli]

CC'ing @rricard @mheiber and @littledan who were part of the conversation regarding this in Class Fields (Stage 3) #12.

I would also like to volunteer to fix this.
@babel-bot
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Hey @ramin25! 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
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@loganfsmyth
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This may well make sense logically, but does the spec actually say that? Since # and IdentifierName are two separate tokens, it seems like having whitespace between them would actually be allowed, the same way whitespace is optional between other tokens.

It seems like this would require new logic in the syntactic grammar itself to assert a lack of whitespace/comments.

@nicolo-ribaudo
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See babel/proposals#12 (comment): white spaces should be disallowed. I don't know how the proposal spec handles this, but if it doesn't it's a bug with the proposal.

@loganfsmyth
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Alright, then is there a spec bug tracking that? I don't see anything in the spec text actually backing this up.

@littledan
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It's subtle, but because the PrivateName production uses two :: rather than one :, it is part of the token grammar, and no whitespace is permitted. We have discussed whether whitespace should be permitted here in TC39 and the decision to treat it as one token with no whitespace was an explicit one.

@loganfsmyth
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@littledan Perfect, that's all I was missing. Like I said, seems like the right thing to do, I just wanted to make sure it was actually specified fully.

@macabeus macabeus mentioned this issue Sep 23, 2018
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@lock lock bot added the outdated A closed issue/PR that is archived due to age. Recommended to make a new issue label Jan 2, 2019
@lock lock bot locked as resolved and limited conversation to collaborators Jan 2, 2019
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@loganfsmyth @littledan @nicolo-ribaudo @ramin25 @babel-bot