First always inferred as mixed in [infer First, ...infer Rest]

[mwiencek]

Flow version: v0.273.1

Expected behavior

type GetFirst = ['a', 'b', 'c'] extends [infer First, ...infer Rest]
    ? First
    : empty;
declare var f: GetFirst;

// this should work
f as 'a';

Actual behavior

Cannot cast f to string literal a because mixed [1] is incompatible with string literal a [2]. [incompatible-cast]

Strangely, First is inferred fine when only using [infer First, ...], or [...infer Rest] + Rest[0]; see the three examples in the Try-Flow.

• Link to Try-Flow or Github repo: https://flow.org/try/#1N4Igxg9gdgZglgcxALlAIwIZoKYBsD6uEEAztvhgE6UYCe+JADpdhgCYowa5kA0I2KAFcAtiRQAXSkOz9sADwxgJ+NPTbYuQ3BMnTZA+Y2yU4IwRO4A6SFBIrGVDGM7c+h46fNRLuKxJIGWh8MeT0ZfhYlCStpHzNsFBAMIQkIEQwJODAQfiEyfBE4eWw2fDgofDBMsAALfAA3KjgsXGxxZC4eAw0G-GhcWn9aY3wWZldu-g1mbGqJUoBaCRHEzrcDEgBrbAk62kXhXFxJ923d-cPRHEpTgyEoMDaqZdW7vKgoOfaSKgOKpqmDA+d4gB5fMA-P6LCCMLLQbiLOoYCqgh6-GDYRYIXYLSgkRZkCR4jpddwPfJLZjpOBkUEKTwJEJ+DAkMiUFSwkyZCC3dbdAC+-EgGiSK2MAAIACpCRhtCUAXglAG0AOQYVW8CWqtCa7VgVUAXQA3AAdKDmgD0lolAHdeVsSObxdgJQBxXYAMTg+IkAEZFdLZfKFAsoGwSCqKpjKBLvb6tVYk4bzRK0xKAPxxn32VPp5AS7AiOG0M3hua4KiuwESmB+gseiTx+x+st1iWs7UastWm0mSi8khaga0CVsOAwGOCSES2kSiS1V0AA2jJglACV2hIl87Vu6vTmJAAmQMyuWu0OCCNR2Br5sSRNJ1exzf2FNQdOZ7O+vNpgtFksyw0J4qwlGsYCPBsD19I82xPTt1VVHsoGtedajnMgi0jNI7QdNCICEBBagAQl3SVG3vABmU9gwveQw2vZUkysZ8Ny3d9PyzV8JGVAAGDj80LYsViAitQPAyioKbQ9KLbaiEO7c1chABoTBIOBoCSBpeKsI8AHZKKsP0QAFIA