Pavel Yaskevich 91dbcfdfcc [ConstraintSystem] Deplay opening generic requirements until after contextual self has been applied ...

While computing a type of member via `getTypeOfMemberReference`
let's delay opening generic requirements associated with function
type until after self constraint has been created, that would give
a chance for contextual types to get propagated and make mismatch
originated in generic requirements much easier to diagnose.

Consider following example:

```swift
struct S<T> {}

extension S where T == Int {
  func foo() {}
}

func test(_ s: S<String>) {
  s.foo()
}
```

`foo` would get opened as `(S<$T>) -> () -> Void` and contextual `self`
type is going to be `S<String>`, so applying that before generic requirement
`$T == Int` would make sure that `$T` gets bound to a contextual
type of `String` and later fails requirement constraint `$T == Int`.

This is much easier to diagnose comparing to `$T` being bound to
`Int` right away due to same-type generic requirement and then
failing an attempt to convert `S<String>` to `S<Int>` while simplifying
self constraint.

Resolves: rdar://problem/46427500
Resolves: rdar://problem/34770265

2019-05-24 11:33:30 -07:00

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