babel: Bug: 7.0.0-beta.0 - export default async function named() {} is broken

Bug report

Input Code

export default async function named(input) {
  return input;
}

Failing demo project: git@gist.github.com:e33790419e48fc6c504e39aa3b35572f.git or https://gist.github.com/Ambroos/e33790419e48fc6c504e39aa3b35572f - scripts in package.json.

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

{
  "scripts": {
    "babelify-ok": "babel input.js --out-file output.js",
  },
  "devDependencies": {
    "babel-cli": "^7.0.0-beta.0",
    "babel-preset-env": "^2.0.0-beta.0"
  },
  "babel": {
    "presets": [
      [
        "env",
        {
          "targets": {
            "browsers": [
              "IE 11",
              "last 3 Chrome versions",
              "last 2 Safari versions",
              "last 2 Firefox versions",
              "Firefox ESR",
              "last 2 Edge versions",
              "last 2 iOS versions"
            ]
          }
        }
      ]
    ]
  }
}

Expected Behavior

Transpiling works as it did in 6.

Current Behavior

TypeError: broken.js: Property declaration of ExportNamedDeclaration expected node to be of a type ["Declaration"] but instead got "ExpressionStatement"
    at Object.validate (project-dir/node_modules/babel-types/lib/definitions/index.js:86:13)
    at Object.validate (project-dir/node_modules/babel-types/lib/index.js:478:9)
    at NodePath._replaceWith (project-dir/node_modules/babel-traverse/lib/path/replacement.js:176:7)
    at NodePath.replaceWith (project-dir/node_modules/babel-traverse/lib/path/replacement.js:160:8)
    at Object.replaceWithOrRemove (project-dir/node_modules/regenerator-transform/lib/util.js:32:10)
    at PluginPass.exit (project-dir/node_modules/regenerator-transform/lib/visit.js:163:14)
    at newFn (project-dir/node_modules/babel-traverse/lib/visitors.js:236:21)
    at NodePath._call (project-dir/node_modules/babel-traverse/lib/path/context.js:68:19)
    at NodePath.call (project-dir/node_modules/babel-traverse/lib/path/context.js:42:17)
    at NodePath.visit (project-dir/node_modules/babel-traverse/lib/path/context.js:112:8)```

Context

Only seems to happen when named async functions are exported in one statement: export default async function name() {...}. Splitting the function definition and export default name works, as does exporting unnamed async functions.

Your Environment

babel-cli 7.0.0-beta.0, babel-env 2.0.0-beta.0

software	version(s)
Babel	7.0.0-beta.0
node	8.5.0
yarn	1.0.2
Operating System	macOS 10.13 Beta (17A358a)

(as you may have noticed, I like bleeding edge/beta stuff)

About this issue

Original URL
State: closed
Created 7 years ago
Reactions: 3
Comments: 16 (6 by maintainers)

Most upvoted comments

I’ve dug in a little further, and I’m pretty confident this is an incompatibility between babylon 6/7 ASTs that affects babel-types@6 in this tree:

└─┬ babel-preset-env@2.0.0-beta.2
  ├─┬ babel-plugin-transform-regenerator@7.0.0-beta.2
  │ └─┬ regenerator-transform@0.10.0
  │   └── babel-types@6.26.0

I assume that regenerator needs to update to babel@7-beta

brokentone on Sep 28, 2017

Not sure, although we should just remove the dependency so this won’t be an issue in the future https://github.com/facebook/regenerator/issues/328

hzoo on Nov 23, 2017

I’m confirming this is still an issue in beta.2, here is a repo/branch reproducing with the following command: ./node_modules/.bin/babel --out-dir lib src/

I did notice that anonymous functions were fixed in this situation (export, default, async). However, named are still not.

brokentone on Sep 27, 2017

@hzoo - I think this still is an issue. Targeting Node 8 with babel-preset-env probably just disables the relevant transform as it may not be needed.

export default async function named()… is still broken as mentioned in my issue. @bradchristensen’s comments are not completely related to this.

Ambroos on Sep 27, 2017