camc314 bbbb4bc5c9 fix(packages/codegen): preserve private-in left operand precedence (#26403) ...

The codegen npm package drops required parentheses when a private-in expression is the left operand of a higher-precedence binary operator. The generated JavaScript can evaluate a different expression and throw a runtime error.

For example, this input returns `2`:

```js
class C {
  #x;
  test(o) {
    return (#x in o) + 1;
  }
}
console.log(new C().test(new C()));
```

The JavaScript printer previously emitted the return expression as:

```js
return #x in o + 1;
```

Because `+` binds more tightly than `in`, that output is parsed as `#x in (o + 1)`. Adding `1` to the object produces a primitive, so the private-field check throws a `TypeError` instead of producing the boolean used by the original addition.

The printer now preserves the grouping:

```js
return (#x in o) + 1;
```

The iterative binary-expression printer already computes the precedence required for each left operand. Its private-in special case discarded that value and passed `PREC_LOWEST` to `printPrivateInExpression`. Passing `v.leftPrecedence` instead lets the existing private-in printer insert the required parentheses.

This preserves grouping for arithmetic, exponentiation, and shift operators. Equal- and lower-precedence operators, such as `<`, `===`, and `&&`, continue to omit unnecessary parentheses. The correction applies to both the ordinary and source-map-enabled JavaScript printer builds and brings this path in line with the Rust codegen fix in #26383.

2026-09-07 15:21:31 +00:00

7.0 KiB

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