Intersection Type not merging objects in array properly

[ErlendS]

Bug Report

🔎 Search Terms

intersection type, intersection type array

🕗 Version & Regression Information

• This changed between versions 4.8.4 and 4.9.4
• This bug also appears in version 3.5.1, 3.3.3

⏯ Playground Link

Playground link with relevant code

💻 Code

interface Colorful {
  color: string;
}
interface Circle {
  radius: number;
}

type ColorfulCircle = Colorful[] & Circle[];

const test: ColorfulCircle = [{
  color: 'red',
  radius: 2
}]

🙁 Actual behavior

radius field gets type error: Object literal may only specify known properties, and 'radius' does not exist in type 'Colorful'

It looks like it is treating it as a union type where only one of the fields can exist.

🙂 Expected behavior

I expected the merging of the types to make color and radius accessible (and required) in the ColorfulCircle type.

[fatcerberus]

ColorfulCircle should be defined as (Colorful & Circle)[].

[ErlendS]

ColorfulCircle should be defined as (Colorful & Circle)[].

Thanks for replying. That would fix this, but it is a contrived example to show the issue. I can't use that fix in the real issue I'm having.

What I am wondering is if the error I am getting now is a bug introduced in TS 4.9 since that used to work. (and the issue also shows up in two other versions, and then seems to be fixed again)

Looking at specs (though depricated) it looks like the intended behaviour of the intersection type would be to merge the two types to something like: Array<{color: string, radius: number}>

[jcalz]

Duplicate of #41874

[ErlendS]

Yes, sorry I didn't find that when searching. Will close this one then.

[ErlendS]

by the way Joe Calzaretta (@jcalz), any idea why my code example seems to work on version 4.8, but not 4.9?