Broken inference of empty object as Record

[javiertury]

TypeScript Version: 3.9.7

Search Terms: empty object, broken inference, Record

Code

export class Bar <
  Key extends string,
  Value extends string
> {
  get foo (): Record<Key, Value> {
    return {}; // [tsserver 2322] [E] Type '{}' is not assignable to type 'Record<Key, Value>'.
  }
}

Expected behavior:

The empty object type should be inferred as Record<Key, Value>

Actual behavior:

[tsserver 2322] [E] Type '{}' is not assignable to type 'Record<Key, Value>'.

Playground Link:

https://www.typescriptlang.org/play/#code/KYDwDg9gTgLgBAYwDYEMDOa4CEVTgHgCg44BpYATzlBmADsATTNGKASzoHMAaYuANRRIArsGohajZqw6dCAPjgBvPp2DwAZhAhwAFAEoAXHABKwBNAb5yFbgKGjFKkiSjrhUOsoC+Abj7ehN5AA

I used the default version in the playground because the nightly version is completely broken and very slow.

Cannot find name 'Record'.(2304)
Return type of public getter 'foo' from exported class has or is using private name 'Record'.(4043)

Related Issues:

This problem is similar but not equal to #14930

[RyanCavanaugh]

This is a correct error.

export class Bar <
  Key extends string,
  Value extends string
> {
  get foo (): Record<Key, Value> {
    return {}; // [tsserver 2322] [E] Type '{}' is not assignable to type 'Record<Key, Value>'.
  }
}
const k = new Bar<"bla", "baz">();
// No error, crashes
k.foo.bla.toLowerCase();

[javiertury]

I thought Record didn't require the property to be defined. Most of the time it's used like this:

type Foo = Record<string, number>;
const foo: Foo = {}; // Ok

But investigating further I see that you are right and this is the expected behavior when the key is a string literal union. Thank you.