Generic index into two types not seen as assignable, even if the two types are identical for all relevant keys about typescript HOT 4 CLOSED

Right, so it's presumably not worth the performance hit to look at K extends keyof Bar and compare Pick<Foo, keyof Bar> to Pick<Bar, keyof Bar> instead of comparing Foo to Bar. Synthesizing the Pick types for every generic assignment would be equivalent to such "exhaustive analysis", I presume?

from typescript.

Right, exactly

from typescript.

the only difference between Foo and Bar occurs in a key that K can never be.

How does one arrive at this conclusion except via exhaustive analysis of possible values of K? Note that from TS's perspective, this example isn't any different from one with

interface Foo {
  a: string,
  b: number,
}

interface Bar {
  a: string,
  b: number,
  c: boolean
}

from typescript.

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

from typescript.