Erroneous generated JS code when incrementing private (hashtag) fields with parenthesis

[mfederczuk]

Bug Report

When incrementing a private class field (using the hashtag-syntax) and the field is put inside parenthesis while the increment operator is outside the parenthesis, invalid JavaScript code is generated.
e.g.: ++(this.#n)

🔎 Search Terms

private hashtag field increment parenthesis

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about private class fields and incrementing/decrementing

⏯ Playground Link

Playground link with relevant code

💻 Code

class Foo {
  #n: number = 0;

  inc() {
    ++(this.#n); // generated JS code here is erroneous
  }
}

const foo = new Foo();
foo.inc();

🙁 Actual behavior

The following code is generated:

++(__classPrivateFieldGet(this, _Foo_n, "f"))

which leads to the error: invalid increment/decrement operand when executing it, since the result of a function cannot be incremented/decremented.

The compiler seems to think that the variable-reference expression is read-only because of the parenthesis.

🙂 Expected behavior

The parenthesis should be ignored by the compiler and the correct code needs to be generated:

__classPrivateFieldSet(this, _Foo_n, (_a = __classPrivateFieldGet(this, _Foo_n, "f"), ++_a), "f")