[Bug]: Invalid "Missing initializer in const declaration" error reported in .d.ts files

[michaldudak]

💻

• Would you like to work on a fix?

How are you using Babel?

Programmatic API (babel.transform, babel.parse)

Input code

import * as babel from "@babel/core";

const source = `
export const foo: string;
`;

babel.parse(source, {
  configFile: false,
  filename: "source.d.ts",
  plugins: ["@babel/plugin-syntax-typescript"],
});

Configuration file name

No response

Configuration

No response

Current and expected behavior

After updating @babel/parser from 7.17.3 to 7.17.7, parsing .d.ts files, as shown above, fails with the following error:

SyntaxError: C:\Users\Michal\Desktop\babel-repro\source.d.ts: Missing initializer in const declaration. (2:24)

  1 |
> 2 | export const foo: string;
    |                         ^
  3 |
    at instantiate (C:\Users\Michal\Desktop\babel-repro\node_modules\@babel\parser\lib\index.js:72:32)
    at constructor (C:\Users\Michal\Desktop\babel-repro\node_modules\@babel\parser\lib\index.js:358:12)
    at Object.raise (C:\Users\Michal\Desktop\babel-repro\node_modules\@babel\parser\lib\index.js:3334:19)
    at Object.parseVar (C:\Users\Michal\Desktop\babel-repro\node_modules\@babel\parser\lib\index.js:15292:16)
    at Object.parseVarStatement (C:\Users\Michal\Desktop\babel-repro\node_modules\@babel\parser\lib\index.js:15085:10)
    at Object.parseVarStatement (C:\Users\Michal\Desktop\babel-repro\node_modules\@babel\parser\lib\index.js:10243:31)
    at Object.parseStatementContent (C:\Users\Michal\Desktop\babel-repro\node_modules\@babel\parser\lib\index.js:14631:21)
    at Object.parseStatementContent (C:\Users\Michal\Desktop\babel-repro\node_modules\@babel\parser\lib\index.js:10284:18)
    at Object.parseStatement (C:\Users\Michal\Desktop\babel-repro\node_modules\@babel\parser\lib\index.js:14556:17)
    at Object.parseExportDeclaration (C:\Users\Michal\Desktop\babel-repro\node_modules\@babel\parser\lib\index.js:15932:17) {
  code: 'BABEL_PARSE_ERROR',
  reasonCode: 'DeclarationMissingInitializer',
  loc: Position { line: 2, column: 24, index: 25 },
  pos: [Getter/Setter]
}

The official TypeScript compiler does not complain about this sample code.

Environment

System:
OS: Windows 10 10.0.19044
Binaries:
Node: 16.17.0 - C:\Program Files\nodejs\node.EXE
Yarn: 1.22.19 - ~\AppData\Roaming\npm\yarn.CMD
npm: 8.15.0 - ~\node_modules.bin\npm.CMD
npmPackages:
@babel/core: ^7.18.13 => 7.18.13
@babel/plugin-syntax-typescript: 7.16.7 => 7.16.7

Possible solution

No response

Additional context

No response

[babel-bot]

Hey @michaldudak! 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]

We should expose the dts option of the typescript plugin of @babel/parser to @babel/plugin-syntax-typescript. As a workaround, try this:

babel.parseSync(source, {
  configFile: false,
  filename: "source.d.ts",
  parserOpts: {
    plugins: [
      ["typescript", { dts: true }]
    ]
  }
});

[nicolo-ribaudo]

@AnmolBansalDEV I saw in other issues that you are looking for a good first issue: this could be it!

@babel/plugin-syntax-typescript currently accepts a disallowAmbiguousJSXLike option, and "forwards" it to the parser:

babel/packages/babel-plugin-syntax-typescript/src/index.ts

Line 41 in ab5b91d

["typescript", { disallowAmbiguousJSXLike }],

We should do something similar for the dts option. You can add a test in https://github.com/babel/babel/tree/main/packages/babel-plugin-syntax-typescript/test/fixtures, adding a folder dts/enabled with the input code as in the above issue description and this config:

{
  "plugins": [["syntax-typescript", { "dts": true }]]
}

[AnmolBansalDEV]

Thank you @nicolo-ribaudo for suggesting! Right now, I'm traveling, I'll start working on this issue next week. Thank you for your cooperation!

[nicolo-ribaudo]

Awesome! I'm assigning this to you :)
Let us know if you need any help!

[oceandrama]

@nicolo-ribaudo I could help with this issue, if @AnmolBansalDEV doesn't mind

[sanyamgandhak]

Hi there ,
Please assign to me

[liuxingbaoyu]

#14923
Hi, this issue has been fixed, just waiting for the minor release,