loose-autocomplete.ts

const colorMap = {
  red: "#f00",
  green: "#0f0",
  blue: "#00f",
} as const;

type Color = keyof typeof colorMap;

type LooseAutocomplete<T extends string> = T | (string & {});

function setColor(color: LooseAutocomplete<Color>) {
  // accepts "red", "green", "blue" with autocomplete
  // also accepts any other string without error
}

// Valid usages
setColor("red");       // ✅ autocomplete
setColor("purple");    // ✅ no autocomplete, but allowed
setColor("green");     // ✅ autocomplete