TS Unable to detect duplicate keys in object when using variables + computed properties

[joshburgess]

TypeScript Version:

3.3.0-dev.201xxxxx

Search Terms:

computed properties, duplicate keys

Code

// type error, as expected
const foo1 = {
  Key1: 1,
  Key1: 2
}

// ok, let's try with computed properties
const Key1 = 'Key1'
const Key2 = 'Key2'

// no type error? widened type to `string`, maybe?
const foo2 = {
  [Key1]: 1,
  [Key1]: 2
}

// type error when literals are used
const foo3 = {
  ['Key1']: 1,
  ['Key1']: 2
}

// now, let's try with enums
enum TestEnum {
  Key1 = 'Key1',
  Key2 = 'Key2'
}

// no type error? widened type to `string`, maybe?
const foo4 = {
  [TestEnum.Key1]: 1,
  [TestEnum.Key1]: 2
}

Expected behavior:

I found some weirdness around how typescript treats computed properties & duplicate keys. I would expect it to detect duplicate keys when passed variables with specific type literals, whether created via constants or enum members.

Actual behavior:

Duplicate keys are not detected when variables are used as computed properties. This is particularly a problem when trying to use enum members, because there is no alternative way to use them as keys in an object.

Playground Link:

https://bit.ly/2TrDznF

Related Issues:

Possibly these:

#26208

#18596

[ajafff]

Duplicate of #25758

[joshburgess]

Whoops. Sorry, @ajafff .

[typescript-bot]

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