index operator and object spread

[bradzacher]

TypeScript Version: 2.4.2

Code

interface HasIndex {
    [key : string] : number
}
interface HasPropWithHasIndex {
    hasIndex ?: HasIndex
}

// one - works fine
const obj1 : HasPropWithHasIndex = {
    hasIndex: {
        a: 1
    }
}

// two - works fine
const test2 = { a: 1 }
const obj2 : HasPropWithHasIndex = {
    hasIndex: test2
}

// three - doesn't work
const obj = {
    a: 1,
    b: 2,
    c: 3,
}
const { a, ...test3 } = obj
// Error: Index signature is missing in type '{ b: number; c: number; }'.
const obj3 : HasPropWithHasIndex = {
    hasIndex: test3,
}

// four - test4 should be of type number, is instead of type any
const test4 = test3['a']

Expected behavior:
The obj3 assignment in test three should work without an issue.
test4 in test four should be of type number

Actual behavior:
The obj3 assignment in test three throws an error: Index signature is missing in type '{ b: number; c: number; }'.
test4 is of type any.

It looks like when you use the spread operator, typescript changes the type of the index operator to return any.

[DanielRosenwasser]

@ahejlsberg, should this work with respect to changes made in #7029?

[olegdunkan]

test2 and {a:1} originates in an object literal, test3 originates from rest type, for test2 and {a:1} we can apply #7029 for test3 probably not, but there is not any info in spec for both cases!!!

[RyanCavanaugh]

This works as expected now

[benhamlin]

This is an old issue but was never actually fixed? You can paste the original code into the playground and all the same errors occur.

[koba04]

@RyanCavanaugh
I think this issue has not been fixed yet.
I've created an example of this. Is it expected behavior that var error: A = rest; is an error, but var ok2: A = {...rest}; is not?

type A = { [key: string]: string };

var obj = { foo: 'foo', bar: 'bar', baz: 'baz'};
const {...rest} = obj;

const mapped: { [a in keyof typeof rest]: string } = rest;

var ok: A = obj;
var ok2: A = {...rest};
var ok3: A = mapped
var error: A = rest;   // An error occurred

https://www.typescriptlang.org/play?#code/C4TwDgpgBAglC8UDeUDaBrCIBcUDOwATgJYB2A5gLq4EkVQC+A3AFAsBuAhoVAPYBGAKwTIoAM169cAcgm9pAGij9uMlYUXLOALzU7pzFgGNepAsgB0VwhAIMRAwa2OnzAW05hIAE1wpUnFBkUJggvGJQoJDhUDYE1PhEZOSMInHAzlw8vOi4cIiOrFl86ABMeSJIVhbphsU5AMwViB5eEN4c3FAQhIS8hM2xthksQA