Spread operator cannot be typed with intersection type

[reverofevil]

🔎 Search Terms

intersection spread

🕗 Version & Regression Information

• I was unable to test this on prior versions because there is no online bisect tool for that, and git clone of TS repo doesn't work on Windows

⏯ Playground Link

https://www.typescriptlang.org/play?#code/MYewdgzgLgBAtgUwE4HMEwLwwDwEEA0MAQgHwAUAhgFwwEwBGNRAlJiTGQN4B0vFhvbvQC+zANwAoCaEiwArphicAHjTKsM7AORbhkmdBgA3RSrUb2ABj3TwhgO6nVHCzChI5CG7dkxlixFQEMjlCQLQyI0J7ZmZuZXVJAHokv24oEAAZEHtkAGEKCHQASwgYMBBYChgAMzkwYChi8B8IEAAbBG52kBQyZXSsnPzC4NixIA

💻 Code

const merge = <A, B>(a: A, b: B) => ({...a, ...b});

const u = {x: () => ''};
const v = {x: () => 0};
const w = {x: () => true};

const x = merge(u, merge(v, w)).x();
// x.toLowerCase is not a function
console.log(x.toLowerCase());

🙁 Actual behavior

TS doesn't see any kind of an issue with the code

🙂 Expected behavior

Property 'toLowerCase' does not exist on type 'boolean'

Additional information about the issue

No response

[RyanCavanaugh]

#50185 (comment)

[reverofevil]

@RyanCavanaugh It links a suggestion/feature request, and this one is surely a bug. Can we mark that one as bug, or unduplicate this one?

[RyanCavanaugh]

Correctly representing this requires a new feature. Missing features aren't bugs - there's no straightforward way to just "fix" this without that feature.

[reverofevil]

It doesn't, really. The type is Exclude<A, keyof B> & B, modulo other bugs in intersections' implementation.

[RyanCavanaugh]

That doesn't correctly handle optional properties.

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.