No constraint for { [P in K]: XXX } where K is type variable

[Anders Hejlsberg (ahejlsberg)]

The following currently produces no errors:

function test1<T, K extends keyof T>(obj: Pick<T, K>) {
    let x = obj.foo;
    let y = obj.sayWhat;
}

function test2<T, K extends keyof T>(obj: Record<K, number>) {
    let x = obj.foo;
    let y = obj.sayWhat;
}

That's obviously not right. This PR removes the code that gets this wrong in resolveMappedTypeMembers.

[Anders Hejlsberg (ahejlsberg)]

TypeScript Bot (@typescript-bot) test this.

[TypeScript Bot (typescript-bot)]

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the extended test suite on this PR at 30d1ecd. You can monitor the build here. It should now contribute to this PR's status checks.

[Anders Hejlsberg (ahejlsberg)]

Looked over the RWC baseline changes. There are new errors in one project, all of which are correct and relate to uses of Pick<T, K> that are strange (e.g. functions with a type parameter K that is never used in the parameter list).