Intersection breaks disjoint unions

[vkurchatkin]

This type-checks, although it shouldn't:

type Common = {
};

type A = Common & {
  type: 'A',
  foo: number
};

type B = Common & {
  type: 'B',
  foo: Array<number>
}

type MyType = A | B;

function print(x: number) {
  console.log(x);
}

function printAll(val: MyType) {
  print(val.foo);  // <--- foo could be an array
}

If I remove intersection it works as expected.

[vkurchatkin]

Interesting thing: order matters. If you declare types like this:

type A = {
  type: 'A',
  foo: number
} & Common;

type B = {
  type: 'B',
  foo: Array<number>
} & Common;

This example begins to fail correctly, but refinement doesn't work anymore:

type Common = {
};

type A = {
  type: 'A',
  foo: number
} & Common;

type B = {
  type: 'B',
  foo: Array<number>
} & Common;

type MyType = A | B;


function print(x: number) {
  console.log(x);
}

function printAll(val: MyType) {
  if (val.type === 'A') {
    print(val.foo);
  } else {
    val.foo.forEach(print);
  }
}

Outputs:

test/good/tmp.js:25
 25:     print(val.foo);
         ^^^^^^^^^^^^^^ function call
 25:     print(val.foo);
               ^^^^^^^ array type. This type is incompatible with
 19: function print(x: number) {
                       ^^^^^^ number

test/good/tmp.js:27
 27:     val.foo.forEach(print);
                 ^^^^^^^ property `forEach`. Property not found in
 27:     val.foo.forEach(print);
         ^^^^^^^ Number


Found 2 errors

[zerkalica]

Any progress on this? How to create unions with common part?

[zerkalica]

duplicate: #1118

[avikchaudhuri]

This will be fixed in an upcoming release.

[zerkalica]

@avikchaudhuri flow 0.27, not fixed for me:
May be related: #1931, #1664

// @flow
type DataBase = {
  id: string;
  name: string;
};

type UserData = DataBase & {
  kind: 'user';
};

type SystemData = DataBase & {
  kind: 'system';
  n: number;
}

type Data = UserData | SystemData;
function test(data: Data): void {
    if (data.kind === 'system') {
        if ((data: SystemData).n === 1) { // Error: this type is incompatible with
            return
        }
    }
}

[maboelsoud]

Any updates on this, I'm using the latest version and this is still a problem.