Wrong Conversion of Let and Const Variables Defined in Block

[clhiker]

Describe the bug

Const and let only exist in the blocks they are defined in, but after swc conversion, they all become var variables and can print value out of the block.

Input code

{
  let a = 1;
  const b = 1;
  var c = 1;
}
console.log(a); 
console.log(b); 
console.log(c);

Config

{
  "jsc": {
    "parser": {
      "syntax": "ecmascript",
      "jsx": false,
      "dynamicImport": false,
      "privateMethod": false,
      "functionBind": false,
      "exportDefaultFrom": false,
      "exportNamespaceFrom": false,
      "decorators": false,
      "decoratorsBeforeExport": false,
      "topLevelAwait": false,
      "importMeta": false
    },
    "transform": null,
    "target": "es5",
    "loose": false,
    "externalHelpers": false
  }
}

Playground link

https://play.swc.rs/?version=1.2.106&code=H4sIAAAAAAAAA6vm5VJQyEktUUhUsFUwtAbxkvPziksUkuD8ssQihWQor5aXCySdn5Oql5OfrpGoaa2AKpKEIZIMFAEAhYlu3mYAAAA%3D&config=H4sIAAAAAAAAA0WMTQrEIAxG75K1286id5hDBCctFv9IUhgR714tlu7C915ehUMsrBUyshCPS0pU%2FMMKZAOKZZcVTNf6tKEXagYUeScdiiyd%2BZSEJjUQXHRbGSWbQmYSeRHG3T9m66GQfucYKmjJdAc%2F0N7G%2FHPynaLySe0Cj9ke9LUAAAA%3D

Expected behavior

const and let only exist in the blocks they are defined in. After transforming, they should like this

// const and let only exist in the blocks they are defined in.
{
  var _a = 1;
  var _b = 1;
  var c = 1;
}
console.log(a); // ReferenceError
console.log(b); // ReferenceError
console.log(c); // Prints 1

or like this
// const and let only exist in the blocks they are defined in.

{
  var a$__0 = 1;
  var b$__1 = 1;
  var c = 1;
}
console.log(a); // ReferenceError
console.log(b); // ReferenceError
console.log(c); // Prints 1

Version

@swc/cli: 0.1.51 @swc/core: 1.2.106

Additional context

I run swc use cmd as follows

npx swc --config-file=.swcrc poc.js -o poc.js

The environment is ubuntu 20.04 amd64.

[swc-bot]

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