Omit<> excludes types from merged interfaces including index types

[Kapcash]

TypeScript Version: v4.1.0-dev.20201008

Search Terms: Omit merged interface, Generic type with declaration merging

Code

interface Todo extends Record<string, any> {
  title: string
  description: string
  completed: boolean
}

interface Todo extends Record<string, any> {
  tags: string[]
}

const todo: Omit<Todo, 'description'> = {
  title: 'Todo 1',
  completed: false,
  tags: [''],
}

const trimedTags = todo.tags.map(tag => tag.trim()) // tags is considered as 'any' here.

Expected behavior:
Using Omit<> on types defining index types ([key: xxx]), the types from merged interface should remain defined and not fallback to the specified index type.

Actual behavior:
Any types from the merged interface are transformed to 'any' or 'unknown', as if they were only part of the index type, but they are actually defined. I expect them to keep their defined type from the merged interface.

It works well using Pick<> though.

Playground Link:

Here is a playground showing the error.

Related Issues:
Indexed access operator issue with Omit type #36316

[andrewbranch]

Duplicate of #31153—@dragomirtitian's OmitFromKnownKeys suggestion solves your problem.

[Kapcash]

Got it, thanks!
And sorry for the duplicate, I wish I found the issue myself.

[andrewbranch]

No worries, duplicates can be hard to find in a haystack of 40k 😄