Incorrect type inference for array rest assignment and inability to add annotation

[theseyi]

TypeScript Version: 2.7.1-insiders.20180127

Search Terms: array destructuring rest assignment

Code

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.
const [stringA, ...numbers] = ['string', 1, 2];
// const [stringA, ...numbers] = <[string, number, number]>['string', 1, 2];
// const [stringA, ...numbers]: [string, number[]] = ['string', 1, 2];
// const [stringA, ...numbers]: [string, [number, number]] = ['string', 1, 2];

Expected behavior: Expect numbers to be of type number[] rather than (string | number)[].
TS also does not allow annotating as a tuple

Actual behavior: const numbers: (string | number)[]

Playground Link: http://www.typescriptlang.org/play/index.html#src=const%20%5BstringA%2C%20...numbers%5D%20%3D%20%5B'string'%2C%201%2C%202%5D%3B%0A%2F%2F%20const%20%5BstringA%2C%20...numbers%5D%20%3D%20%3C%5Bstring%2C%20number%2C%20number%5D%3E%5B'string'%2C%201%2C%202%5D%3B%0A%2F%2F%20const%20%5BstringA%2C%20...numbers%5D%3A%20%5Bstring%2C%20number%5B%5D%5D%20%3D%20%5B'string'%2C%201%2C%202%5D%3B%0A%2F%2F%20const%20%5BstringA%2C%20...numbers%5D%3A%20%5Bstring%2C%20%5Bnumber%2C%20number%5D%5D%20%3D%20%5B'string'%2C%201%2C%202%5D%3B

Related Issues:

[mhegazy]

Duplicate of #3369. A tuple type is not inferred in the absence of an explicit type annotation.

you can find related discussions in #16656

[theseyi]

A tuple type is not inferred in the absence of an explicit type annotation

@mhegazy so how would the numbers rest assignment be annotated as a tuple? I believe I tried to this in the last line:

const [stringA, ...numbers]: [string, [number, number]] = ['string', 1, 2];

[mhegazy]

The right type should be const [stringA, ...numbers]: [string, number, number]. and numbers should be inferred correctly. that is a bug we should fix.

[sandangel]

I have run into this issue too with overload function

// I have tried this but it does not work
interface OperatorTuple extends Array<OperatorFunction<any, any>> {
  0: OperatorFunction<any, any>;
  1: OperatorFunction<any, any>;
  2: OperatorFunction<any, any>;
  3: OperatorFunction<any, any>;
  4: OperatorFunction<any, any>;
  5: OperatorFunction<any, any>;
  6: OperatorFunction<any, any>;
  7: OperatorFunction<any, any>;
  length: 8;
}

// this is an overload function
export function Select<A, B>(mapFn: ((state: A) => B), ...operators: OperatorFunction<any, any>[]) {
  return function(target: any, name: string): void {
    if (typeof mapFn !== 'function') {
      throw new TypeError(
        `Unexpected type '${typeof mapFn}' in select operator,` + ` expected 'function'`
      );
    }

    // trying to cast type tuple
    operators = [...operators] as OperatorTuple;

    const descriptor = Object.getOwnPropertyDescriptor(target, name);

    if (delete target[name]) {
      Object.defineProperty(target, name, {
        get() {
          const source$ = NgrxSelect.store;

          if (!source$) {
            throw new Error('NgrxSelect not connected to store!');
          }

         // I have tried this too but have failed
         if (operators.length > 8) {
            throw new Error()
         }
          
          // Error: Expect 0-9 arguments but received 1 or more
          return source$.pipe(select(mapFn), ...operators);
        },
        ...descriptor
      });
    }
  };
}