Flow-compatible string object type that does not interfere with auto-completion

[refirst11]

In StyleXCSSTypes.js, some types include both string literals and the primitive string type:

type fontWeight =
  | 'normal'
  | 'bold'
  | 'bold'
  | 'bolder'
  | 'lighter'
  | ...
  | string  // ← suppresses all string literal candidates
  | number;

In TypeScript and JavaScript (via d.ts), the primitive string absorbs all string literal types in a union, causing autocomplete candidates to disappear entirely.

Since StyleX$Create uses S as a generic argument type, no actual type checking is performed on values anyway:

<const S extends ...>(styles: S) => ...

This means string serves only as an index, not a validator. Replacing it with string & {} would preserve the open-ended nature of the type while restoring autocomplete for the listed literals.

---

I tested and confirmed that flow-bin cannot compile to d.ts.

Pick<string, keyof string>
Omit<string, never>
string & {}

However, since there are currently few cases where actual harm is being caused, I simply wanted to share this as a potential area for improvement.

[refirst11]

After exploring other methods, I tested the completion speed.

{ valueOf(): string }

The fastest time recorded was 0.06ms.
The average was around 0.12ms.

This was the most concise way to write it compared to other cases such as & {}, Pick, and Record. This is type-compilation compatible with flow-bin.

[henryqdineen]

👍 I also suggested the string & {} trick in #1466. It would be a good improvement.