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`Duplicate declaration` error with Babel 7, typescript preset and namespace #10038

ikenik opened this issue May 29, 2019 · 1 comment


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commented May 29, 2019

Bug Report

Current Behavior

Transpilation of the code fails with the following error.

TypeError: D:\Git\babel-duplicate-declaration-example\example.ts: Duplicate declaration "foo"
   6 |     }
   7 |     export namespace ns2 {
>  8 |         export class foo {
     |                      ^
   9 |             F1: string;
  10 |         }
  11 |     }
    at File.buildCodeFrameError (D:\Git\babel-duplicate-declaration-example\node_modules\@babel\core\lib\transformation\file\file.js:261:12)
    at Scope.checkBlockScopedCollisions (D:\Git\babel-duplicate-declaration-example\node_modules\@babel\traverse\lib\scope\index.js:344:22)
    at Scope.registerBinding (D:\Git\babel-duplicate-declaration-example\node_modules\@babel\traverse\lib\scope\index.js:501:16)
    at Scope.registerDeclaration (D:\Git\babel-duplicate-declaration-example\node_modules\@babel\traverse\lib\scope\index.js:444:12)
    at Object.BlockScoped (D:\Git\babel-duplicate-declaration-example\node_modules\@babel\traverse\lib\scope\index.js:187:28)
    at Object.newFn (D:\Git\babel-duplicate-declaration-example\node_modules\@babel\traverse\lib\visitors.js:230:17)
    at NodePath._call (D:\Git\babel-duplicate-declaration-example\node_modules\@babel\traverse\lib\path\context.js:53:20)
    at (D:\Git\babel-duplicate-declaration-example\node_modules\@babel\traverse\lib\path\context.js:36:14)
    at NodePath.visit (D:\Git\babel-duplicate-declaration-example\node_modules\@babel\traverse\lib\path\context.js:88:12)
    at TraversalContext.visitQueue (D:\Git\babel-duplicate-declaration-example\node_modules\@babel\traverse\lib\context.js:118:16)

Input Code

// typescript
module src {
    export namespace ns1 {
        export class foo {
            F1: string;
    export namespace ns2 {
        export class foo {
            F1: string;

Expected behavior/code
A clear and concise description of what you expected to happen (or code).

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

    presets: ["@babel/preset-typescript"]
  "dependencies": {
    "@babel/core": "^7.4.5"
  "devDependencies": {
    "@babel/preset-typescript": "^7.3.3"
npm install
npm start


  • Babel version(s): v7.4.5
  • Node/npm version: Tested and confirmed in Node 8/9/10 with npm 5.6.0
  • OS: Windows 10
  • Monorepo: no
  • How you are using Babel: cli

Additional context/Screenshots

#8559, #8525 may be related.


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commented May 29, 2019

Hey @ikenik! 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
that typically always has someone willing to help. You can sign-up here
for an invite.

@ikenik ikenik changed the title `Duplicate declaration` error with Babel 7, typescropt preset and namespace `Duplicate declaration` error with Babel 7, typescript preset and namespace May 29, 2019

@nicolo-ribaudo nicolo-ribaudo referenced a pull request that will close this issue May 29, 2019


Implement TypeScript namespace support #9785

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