Simple downlevelled optional chain generates an extra, unnecessary variable

[bradzacher]

Describe the bug

It looks like SWC's logic is defined to always add a variable for optional chaining, even when it's unnecessary.

This generates a number of extra bytes that could otherwise be avoided.

Input code

export function foo(arg) {
  arg?.foo();
}

Config

{
  "jsc": {
    "parser": {
      "syntax": "typescript"
    },
    "target": "es2019",
    "transform": {
      "optimizer": {
        "simplify": true
      }
    }
  },
  "sourceMaps": true
}

Playground link

https://play.swc.rs/?version=1.3.74&code=H4sIAAAAAAAAA0utKMgvKlFIK81LLsnMz1NIy8%2FXSCxK11So5lJQADLs9UAimtZctVwAufDgFisAAAA%3D&config=H4sIAAAAAAAAA11Su27DMAzc8xWG5gxthwLt2BhBO3TqFxAKHbDQCyQF2A3y75Xs2HG8COIddTySuuyaxlBwFPAnZrYohxgUg5r3RjnjvvK%2FYkt4KdcSYK%2FIAdwnuoQsq7xCJmBBXpILIkNQ6AtidEgolimp2c%2FsCW1k0LjRqcwQwJP98imybkmV%2FgaNyPVWXYHPWJMNysvT85uZcYYgXWS%2FNpYFW%2BxK38fIBwciR0J3qj46cHKv5fAMdmhno1srjGB1pVuhHJQ8Vh%2BQNXpQskvLU%2BWPTE4pyLqLpY%2BSElNRoL%2BHUdZhkk%2BOumHzbDefo4Dx8ZQd3jdG5xAZ22mgj%2FuqO5nm9WqW9zJ%2BhG9Ii73rP1R%2Fu4gnAgAA

SWC Info output

No response

Expected behavior

Output should be

export function foo(arg) {
    arg === null || arg === void 0 ? void 0 : arg.foo();
}

Actual behavior

Output is

export function foo(arg) {
    var _arg;
    (_arg = arg) === null || _arg === void 0 ? void 0 : _arg.foo();
}

Version

1.3.74

Additional context

No response

[bradzacher]

Why is this a problem?

1. It generates a lot more bytes than are necessary
2. In some cases it causes even more code to be generated than necessary. EG in a bodyless arrow function SWC will insert a body when it doesn't need to:

// input
export const foo = (arg) => arg?.foo();

// expected output
export const foo = (arg) => arg === null || arg === void 0 ? void 0 : arg.foo();

// actual output
export const foo = (arg)=>{
    var _arg;
    return (_arg = arg) === null || _arg === void 0 ? void 0 : _arg.foo();
};

playground

[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.