ES2015::block_scoping renames exports

[fatso83]

Describe the bug

I was writing a how-to on using a new Sinon feature for auto-cleanup of stubs injected using accessors when I discovered it did not work when I exposed accessors on an exported object called 'mock'.

Basically, if I write something like this:

export const mock = {
    get toBeMocked(){ return toBeMocked; },
    set toBeMocked(mock){ toBeMocked = mock; }
}

it will be transpiled to this by SWC, which is very different from tsc:

export const _$mock = {
    get toBeMocked(){ return toBeMocked; },
    set toBeMocked(mock){ toBeMocked = mock; }
}

Somehow 'mock' gets turned into _$mock.

To run this example, just do

gh repo clone fatso83/sinon-swc-bug
cd sinon-swc-bug
git checkout swc-special-handling-mock
npm install
npm test

This is not a typescript issue, btw, as the playground shows the issue with a minimal example

Input code

// The entire runnable example is here: 
// https://github.com/fatso83/sinon-swc-bug/tree/swc-special-handling-mock

function _toBeMocked() {
  return "I am the original function";
}

export let toBeMocked = _toBeMocked

export const mock = {
    get toBeMocked(){ return toBeMocked; },
    set toBeMocked(mock){ toBeMocked = mock; }
}

Config

{
    "test": ".*.ts$",
    "jsc": {
      "parser": {
        "syntax": "typescript",
        "decorators": true
      },
      "transform": {
        "legacyDecorator": true,
        "decoratorMetadata": true
      }
    },
    "module": {
      "type": "commonjs"
    }
  }

Playground link (or link to the minimal reproduction)

https://play.swc.rs/?version=1.3.94-nightly-20231016.1&code=H4sIAAAAAAAAA1WNQQrCMBBF93OKT1cteIPixp0LzyAlTmuwnZF0CkLJ3ZuIWrP9vP9ev4gzr4Kr6Ykv6h58qxusBAS2JQiqM7oJdmdo8IOXbkT%2FOVUtRSJ%2BPTUYRjbsDhz%2FjT%2FIqcyGKY0JyBFgKH51s37D%2B9giHt7sXLLZk%2FiimrfEU9wALRrz29oAAAA%3D&config=H4sIAAAAAAAAA1WPSw7DIAwF9zkF8rrbdtE79BAWdSIifrKJVBTl7iUE0maH3xsz8jooBbNoeKq1PMsQkYX4nEsi2Sf8lARIOxTNJia49XaWvRrRCtVoOxpIyBOluiX3hoMNQajjLXPGmzH%2FC3VwkUnkCu4o%2BsnSVTc0JbjwXmrZDkk50qF%2FwA%2FqsvNjMPLqm4kXGrYvhlQioBQBAAA%3D

SWC Info output

Operating System:
    Platform: darwin
    Arch: arm64
    Machine Type: arm64
    Version: Darwin Kernel Version 23.0.0: Fri Sep 15 14:43:05 PDT 2023; root:xnu-10002.1.13~1/RELEASE_ARM64_T6020
    CPU: (12 cores)
        Models: Apple M2 Max

Binaries:
    Node: 20.5.0
    npm: 9.8.0
    Yarn: 1.22.19
    pnpm: 7.13.0

Relevant Packages:
    @swc/core: 1.3.76
    @swc/helpers: N/A
    @swc/types: N/A
    typescript: 5.1.6

SWC Config:
    output: N/A
    .swcrc path: N/A

Next.js info:
    output: N/A

Expected behavior

This code:

export const mock = {
    get toBeMocked(){ return toBeMocked; },
    set toBeMocked(mock){ toBeMocked = mock; }
}

should be pretty much unaltered when compiled to ES5 with ESM exports. Probably something like this

function _toBeMocked() {
    return "I am the original function";
}
export var toBeMocked = _toBeMocked;
export var mock = {
    get toBeMocked () {
        return toBeMocked;
    },
    set toBeMocked (mock){
        toBeMocked = mock;
    }
};

Actual behavior

The export is called _$mock instead of mock

function _toBeMocked() {
    return "I am the original function";
}
export var toBeMocked = _toBeMocked;
export var _$mock = {
    get toBeMocked () {
        return toBeMocked;
    },
    set toBeMocked (mock){
        toBeMocked = mock;
    }
};

Version

1.3.94

Additional context

Originally posted as question on the Q&A.

Just play with the playground. It will show in any combination using ES5 as the target

[kdy1]

It's not mock being special.

https://play.swc.rs/?version=1.3.94-nightly-20231016.1&code=H4sIAAAAAAAAA1WNMQrCQBBF%2BznFJ1UCNtbBxs7CM0hYJ3ExmZHNBISwd3dd1Ljt5733%2B0WceRVcTI98Vnfna91gJSCwLUFQndBNsBtDgx%2B8dCP6j1S1FIn4%2BdBgGNmwNXD4L%2F4gpzIbpjTuE%2FF%2BAYZCrJv1%2B7yNLeIus3PJ5lASit88JoPiC5A3bAvdAAAA&config=H4sIAAAAAAAAA1WPSw7DIAwF9zkF8rrbdtE79BAWdSIifrKJVBTl7iUE0maH3xsz8jooBbNoeKq1PMsQkYX4nEsi2Sf8lARIOxTNJia49XaWvRrRCtVoOxpIyBOluiX3hoMNQajjLXPGmzH%2FC3VwkUnkCu4o%2BsnSVTc0JbjwXmrZDkk50qF%2FwA%2FqsvNjMPLqm4kXGrYvhlQioBQBAAA%3D

It's about var scoping

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.