Suyash Srijan 8f44a0bd66 [TypeChecker] Diagnose key paths with contextual type but no leading dot ...

If a Swift key path has root type inferred but does not have a leading dot,
then diagnose it, because it's not valid.

For example:

```swift
struct Foo {
  let property: [Int] = []
  let kp: KeyPath<Foo, Int> = \property.count // error
}
```

Resolves SR-12290
Resolves rdar://problem/59874355

2020-04-07 16:59:23 -07:00

..

keypath

[TypeChecker] Diagnose key paths with contextual type but no leading dot

2020-04-07 16:59:23 -07:00