@babel/preset-typescript and generic arrow function (<T extends {}>)

[Tsury]

Bug Report

Current Behavior
I have an anonymous generic arrow function which looks like this:
const myFunc = <T extends {}>(params: any): any => { }

I'm using vscode and everything is fine, but when I try to build, I get this error from babel-loader:
Unexpected token, expected ";"

Input Code

• REPL or Repo link if applicable:

`const myFunc = <T extends {}>(params: any): any => { }`

Expected behavior/code
Should just build my code

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

My .babelrc has this global preset:

  "presets": [
    "@babel/preset-typescript"
  ],

and this env preset:
["@babel/preset-react", { "development": true }]

These global plugins:

    ["@babel/plugin-proposal-decorators", { "legacy" : true }],
    ["@babel/plugin-proposal-class-properties", { "loose" : true }],
    "@babel/plugin-syntax-dynamic-import",
    ["import", { "libraryName": "antd", "style": true }]

And these env plugins:

        ["@babel/plugin-transform-react-display-name"],
        ["emotion", { "sourceMap": true, "autoLabel": true }]

babel-loader in webpack has no additional settings to the .babelrc file.

Environment

• Babel version(s): 7.1.6
• Node/npm version: Node 11.0.0/npm 6.2.0
• OS: Windows 10
• How you are using Babel: loader

Possible Solution

Additional context/Screenshots
Add any other context about the problem here. If applicable, add screenshots to help explain.

[babel-bot]

Hey @Tsury! 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.

[nicolo-ribaudo]

This seems to work on master

[lapto]

Have the same issue, we had to return to react-native-typescript-transformer.

#7504 is probably related.

[danez]

I'm not able to reproduce this with 7.1.6. Would you be able to paste the complete stacktrace?

[lapto]

@danez Im running it using react-native. Seems like metro is stingy with its stacktrace but here it is:

export const test = async <P extends IP>(body: IE<P>): Promise<void> => {

at _class.raise (*/node_modules/@babel/parser/lib/index.js:4028:15) at _class.unexpected (*/node_modules/@babel/parser/lib/index.js:5343:16) at _class.semicolon (*/node_modules/@babel/parser/lib/index.js:5327:40) at _class.parseVarStatement (*/node_modules/@babel/parser/lib/index.js:7729:10) at _class.parseStatementContent (*/node_modules/@babel/parser/lib/index.js:7327:21) at _class.parseStatementContent (*/node_modules/@babel/parser/lib/index.js:10082:58) at _class.parseStatement (*/node_modules/@babel/parser/lib/index.js:7277:17) at _class.parseExportDeclaration (*/node_modules/@babel/parser/lib/index.js:8365:17) at _class.parseExportDeclaration (*/node_modules/@babel/parser/lib/index.js:10200:68) at _class.parseExport (*/node_modules/@babel/parser/lib/index.js:8312:31)

I checked the version written in package.json of node_mules/@babel and its "version": "7.1.6",

[e-r-w]

If it helps, I've come across this issue too:

const someFunc = () => Promise.resolve(1);

export const worksFine = async <T>(thing: T): Promise<T> => {
  return someFunc().then(() => thing);
};

export const itsBroken = async <T>(thing: T): Promise<T> => {
  return await someFunc().then(() => thing);
};

Seems to break when you have the await keyword mixed in with generic arrow functions. @babel/core 7.1.6.

[danez]

The problem with typescript and async/await has been fixed in #9055 and will be released with 7.2.0.

[danez]

Please try again. It should work now with 7.2.0, as we fixed several issues mentioned in this issue.

If there are still problems please open new issues for them. Thank you.