Re-export statements are omitted from output using @babel/plugin-transform-typescript@7.5.0

[elliottsj]

Bug Report

Current Behavior
Using @babel/plugin-transform-typescript@7.5.0 via @babel/preset-typescript@7.3.3, re-export statements are omitted from the transpiled output.

Repro:

$ npm install @babel/cli @babel/core @babel/preset-typescript
$ echo "export { bar } from './bar';" > script.ts
$ ./node_modules/.bin/babel --presets @babel/preset-typescript script.ts


$ # observe: the above output is empty

Note that separate import + export statements transpile properly:

$ echo "import { bar } from './bar'; export { bar };" > script.ts
$ ./node_modules/.bin/babel --presets @babel/preset-typescript script.ts
import { bar } from './bar';
export { bar };

$ # observe: the output is as expected

Input Code

export { bar } from './bar';

Expected behavior/code
The re-export statement should be included in the output.

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

{
  "presets": ["@babel/preset-typescript"]
}

Environment

• Babel version(s):

  $ npm ls --depth=1                                                                                                                                                                                                                                          (522ms)
  /Users/spencerelliott/Dev/temp
  ├─┬ @babel/cli@7.5.0
  │ ├── chokidar@2.1.6
  │ ├── commander@2.20.0
  │ ├── convert-source-map@1.6.0
  │ ├── fs-readdir-recursive@1.1.0
  │ ├── glob@7.1.4
  │ ├── lodash@4.17.11
  │ ├── mkdirp@0.5.1
  │ ├── output-file-sync@2.0.1
  │ ├── slash@2.0.0
  │ └── source-map@0.5.7
  ├─┬ @babel/core@7.5.0
  │ ├── @babel/code-frame@7.0.0
  │ ├── @babel/generator@7.5.0
  │ ├── @babel/helpers@7.5.0
  │ ├── @babel/parser@7.5.0
  │ ├── @babel/template@7.4.4
  │ ├── @babel/traverse@7.5.0
  │ ├── @babel/types@7.5.0
  │ ├── convert-source-map@1.6.0 deduped
  │ ├── debug@4.1.1 extraneous
  │ ├── json5@2.1.0
  │ ├── lodash@4.17.11 deduped
  │ ├── resolve@1.11.1
  │ ├── semver@5.7.0
  │ └── source-map@0.5.7 deduped
  └─┬ @babel/preset-typescript@7.3.3
    ├── @babel/helper-plugin-utils@7.0.0
    └── @babel/plugin-transform-typescript@7.5.0
  

• Node/npm version: Node v10.15.0, npm 6.9.0

• OS: macOS 10.14.5

• Monorepo: no

• How you are using Babel: see above

[babel-bot]

Hey @elliottsj! 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.

[hzoo]

Ah thanks for the report! I did want to confirm, is this only happening with the TS plugin?

edit: looking at https://github.com/babel/babel/releases/tag/v7.5.0 there's a few TS PRs. I'm thinking it's from #10034, so might not be too hard of a fix cc @Wolvereness? @airato

I would pin to the TS plugin to 7.4.5 for now, apologies!

[elliottsj]

Yes, I've only noticed this issue with the TS plugin. Pinned to 7.4.5 for now. Thanks!

[eyousefifar]

I'm having the same problem

[Turbo87]

I just stepped through this after running into the same issue and I can confirm that 8d492b1 is the issue. The only change to that part of the code since v7.4.5 was that particular commit.

[Wolvereness]

Just to confirm, 2080042 and a6392bd do not have the issue?

[pixelass]

I noticed that all my default exports were missing.

export default "foo"

with 7.5.0

var _default = "foo";
;

with 7.4.5

const _default = "foo";
var _default2 = _default;
exports.default = _default2;
;

@Wolvereness related to a6392bd

[JLHwung]

@Wolvereness Hi I just figure out a quick fix of this issue and it works well on my cases. Are you also working on a fix? If so I would leave it as-is and stop here.

diff --git a/packages/babel-plugin-transform-typescript/src/index.js b/packages/babel-plugin-transform-typescript/src/index.js
index a768907a5..79ca00102 100644
--- a/packages/babel-plugin-transform-typescript/src/index.js
+++ b/packages/babel-plugin-transform-typescript/src/index.js
@@ -98,9 +98,10 @@ export default declare(
         ExportNamedDeclaration(path) {
           // remove export declaration if it's exporting only types
           if (
+            !path.node.source &&
             path.node.specifiers.length > 0 &&
             !path.node.specifiers.find(exportSpecifier =>
-              path.scope.hasOwnBinding(exportSpecifier.local.name),
+              path.scope.hasBinding(exportSpecifier.local.name),
             )
           ) {
             path.remove();
@@ -109,7 +110,10 @@ export default declare(
 
         ExportSpecifier(path) {
           // remove type exports
-          if (!path.scope.hasOwnBinding(path.node.local.name)) {
+          if (
+            !path.parent.source &&
+            !path.scope.hasBinding(path.node.local.name)
+          ) {
             path.remove();
           }
         },
@@ -118,7 +122,7 @@ export default declare(
           // remove whole declaration if it's exporting a TS type
           if (
             t.isIdentifier(path.node.declaration) &&
-            !path.scope.hasOwnBinding(path.node.declaration.name)
+            !path.scope.hasBinding(path.node.declaration.name)
           ) {
             path.remove();
           }

[Wolvereness]

Edit: was told I may have messed up the tests - updated with reruns, and this is only babel-plugin-transform-typescript

bff79e1 (fix commit):

• Input:

  export default "foo";

  Output:

  export default "foo";

• Input:

  export { bar } from './bar';

  Output:

  export { bar } from './bar';

• Input:

  export default "foo";
  export { bar } from './bar';

  Output:

  export default "foo";
  export { bar } from './bar';

bff79e1~1:

• Input:

  export default "foo";

  Output:

  export default "foo";

• Input:

  export { bar } from './bar';

  Output:

• Input:

  export default "foo";
  export { bar } from './bar';

  Output:

  export default "foo";

8d492b1 (my rewrite commit):

• Input:

  export default "foo";

  Output:

  export default "foo";

• Input:

  export { bar } from './bar';

  Output:

• Input:

  export default "foo";
  export { bar } from './bar';

  Output:

  export default "foo";

8d492b1~1:

• Input:

  export default "foo";

  Output:

  export default "foo";

• Input:

  export { bar } from './bar';

  Output:

  export { bar } from './bar';

• Input:

  export default "foo";
  export { bar } from './bar';

  Output:

  export default "foo";
  export { bar } from './bar';

a6392bd:

• Input:

  export default "foo";

  Output:

  export default "foo";

• Input:

  export { bar } from './bar';

  Output:

  export { bar } from './bar';

• Input:

  export default "foo";
  export { bar } from './bar';

  Output:

  export default "foo";
  export { bar } from './bar';

2080042 No change from parent:

• Input:

  export default "foo";

  Output:

  export default "foo";

• Input:

  export { bar } from './bar';

  Output:

  export { bar } from './bar';

• Input:

  export default "foo";
  export { bar } from './bar';

  Output:

  export default "foo";
  export { bar } from './bar';

2080042~1

• Input:

  export default "foo";

  Output:

  export default "foo";

• Input:

  export { bar } from './bar';

  Output:

  export { bar } from './bar';

• Input:

  export default "foo";
  export { bar } from './bar';

  Output:

  export default "foo";
  export { bar } from './bar';

@pixelass - Your issue is probably unrelated based on these tests.

[qiqiboy]

This issue seems still exists in v7.5.1.

[JoshRobertson]

In my case:
In 7.5.0 compilation was successful but would throw an error at runtime.
In 7.5.1 compilation fails with an export was not found error, which is the same error I had with 7.4.5. So I'm stuck on 7.4.4 still.

[nicolo-ribaudo]

@qiqiboy @JoshRobertson Can you share your code?

[JoshRobertson]

@nicolo-ribaudo

sample repo here: https://github.com/JoshRobertson/babel-typescript-issue

[nicolo-ribaudo]

@JoshRobertson Babel can't handle re-exports of TypeScript types, since we don't do cross-file analysis and by looking at this code:

export { Avatar, AvatarProps } from "./Avatar";

it's impossible to know that AvatarProps is a type.

Since usages of AvatarProps will be removed anyway, you can safely ignore the webpack warning: it tells you that something can't be exported, but it isn't being used anyway.

If you want to make that warning go away, you can "hint" Babel that AvatarProps is a type by using it as such:

export { Avatar } from "./Avatar";

import { AvatarProps as Props } from "./Avatar";
export type AvatarProps = Props;

[qiqiboy]

.babelrc

{
  "plugins": ["react-hot-loader/babel", "@babel/plugin-transform-typescript"]
}

Input:

export defualt 'Foo';

Output:

const _default = 'Foo';
; // what???

May this is related with react-hot-loader? I think it's because the updates from >=v7.5.0 make some third-party plugins incompatible.

[nicolo-ribaudo]

Yes, it is a problem with react-hot-loader. A plugin is responsible of maintaining scope information up-to-date, and Babel 7.5.0 brought to the surface that bug in react-hot-loader/babel because it uses scope information to remove exports.
I'm surprised that this didn't come up before, since we use scope info in many other places.

Would you be willing to open a PR to that package (or open an issue)?
https://github.com/gaearon/react-hot-loader/blob/master/src/babel.dev.js#L118
insertBefore returns an array of ast paths, and that plugin should call path.scope.registerDeclaration(resultOfInsertBefore[0])

[theKashey]

So that stuff was there for years, and everybody was just lucky :)

[theKashey]

If someone could verify gaearon/react-hot-loader#1293 with a patch @nicolo-ribaudo proposed - I'll issue a new version of React-Hot-Loader.
I was unable to find documentation for registerDeclaration and have no tests previously red, so you are the ones, who could say "👍"

[sciyoshi]

Seems to be fixed for me by updating react-hot-loader to 4.12.5 with gaearon/react-hot-loader#1293 Thank you @theKashey @nicolo-ribaudo!

[nicolo-ribaudo]

We just released Babel 7.5.2. Please check that in your lockfile it contains v7.5.2 of @babel/plugin-transform-typescript!