Proposal Inferred Partial type

[Hideman85]

I have really no idea how to call this helper, but let me describe the use case.

// Lets imagine I have an options type
type Options {
  readOnly?: boolean;
  required?: boolean;
  filters?: Record<string, string>;
  // ...
}

// Now lets see how I can use in a function
const buildOptions(required: boolean, name: string, team?: string) => {
  const options: Options = {
     required,
     filters: {
       name,
     },
   };
   
   if (team) {
     // Issue is that filters even if defined above remains optional/partial
     options.filters.team = team;
   }
}

// Today we could manuall build the correct type as
const options: Options & Pick<Required<NonNullable<Options>>, 'required' | 'filters'> = {...}

// Issue is when adding more property you always need to add the property in the list
// I tried the following without success to infer the type without explicitely giving the keys
export const makeInferredPartial = <Base, Real extends Required<NonNullable<Base>>>(
  // partial: {[Key in keyof Base]: Required<NonNullable<Base>>[Key]} extends infer Return ? Partial<Base> & Return : never,
  partial: Real,
) => partial;

const options = makeInferredPartial<Options>({
  filters: { name: 'Hello world' },
})
// Would expect the type to be like
{
  readOnly?: boolean;
  required?: boolean;
  filters: Record<string, string>; // Note it become defined
  // ...
}
// Then the following works
options.filters.team = 'admin';

Please let me know if that make sense and if you could help me to build this helper. I think this become pretty useful when the type has plenty of props and you just want to define them and infer the correct typing.

Thanks in advance for your help.

[papb]

Can't you just let options be typed automatically, and enforce the return type of your buildOptions function instead?

function buildOptions(required: boolean, name: string, team?: string): Options {
  const options = {
     required,
     filters: {
       name,
     },
   };
   
   if (team) {
     options.filters.team = team;
   }

   return options;
}

[Hideman85]

In this way you do not get the other properties neither the real type of them 'foo' | 'bar' !== string.