Infer string literal object keys

[solid linden]

Frosk#6439

Playground Link

Preview:```ts
const fields = {
[field0]: 1,
}
type Fields = typeof fields
// ^?

const fieldsLiteral = {
[field${0}]: 1,
}
type FieldsLiteral = typeof fieldsLiteral
// ^?
// Note the {[x: string]: number} type

const fieldsLiteralAsConst = {
[field${0} as const]: 1,
...```

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[hasty lichen]

Is it possible to get {field0: number} through narrowing instead of writing as const?

More specifically, I have something like

const fields = {
  [`field${0}a`]: 'a',
  [`field${0}b`]: 1,
}

// --> typeof fields = {
    [x: string]: string | number;
} 
//I would like it to not create a union like so:

const fieldsAsConst = {
  [`field${0}a` as const]: 'a',
  [`field${0}b` as const]: 1,
}

// --> typeof fieldsAsConst = {
    field0a: string;
    field0b: number;
}

[north glacier]

try satisfies { [k: string]: unknown; }

[hasty lichen]

you are likely right, but I was hoping to avoid having the user write additional syntax that could be easily forgotten

[north glacier]

then you'd need a function

[solid linden]

function foo<T extends { [k: string]: unknown; }>(obj: T) { return obj; }
const fields = foo({
//    ^? - const fields: {
//        [x: string]: string | number;
//    }
  [`field${0}a`]: 'a',
  [`field${0}b`]: 1,
});

[north glacier]

dang

[solid linden]

const what = {
//    ^? - const what: {
//        readonly [x: string]: "a" | 1;
//    }
  [`field${0}a`]: 'a',
  [`field${0}b`]: 1,
} as const;

[north glacier]

ouch

so i guess it's not possible

[hasty lichen]

yeah each key must be as const

[north glacier]

yeah that kinda sucks