swift234

Fix <rdar://problem/19746552> QoI: variable "used before being initialized" instead of "returned uninitialized" in address-only enum/struct

Teach DI about a pattern in address-only struct/enum initializers, improving diagnostics
on code like:

struct S<T, U> {
    let a : T?
    let b : U?
    
    init(a : T) {
        self.a = a
    }
}

enum E<T> {
  case X(T), Y
  
  init() {
  }
}

from:

t.swift:7:5: error: variable 'self.b' used before being initialized
    }
    ^
t.swift:14:3: error: variable 'self' used before being initialized
  }
  ^

To:

t.swift:7:5: error: return from initializer without initializing all stored properties
    }
    ^
t.swift:3:9: note: 'self.b' not initialized
    let b : U?
        ^
t.swift:14:3: error: return from enum initializer method without storing to 'self'
  }
  ^




Swift SVN r25528