Sema: Remove a workaround for an accessibility problem in the standard library

Author: slavapestov

lib/Sema/TypeCheckProtocol.cpp

@@ -2268,9 +2268,7 @@ void ConformanceChecker::recordTypeWitness(AssociatedTypeDecl *assocType,
     aliasDecl->getAliasType()->setRecursiveProperties(
         type->getRecursiveProperties());
 
-    Type interfaceTy = aliasDecl->getAliasType();
-    if (interfaceTy->hasArchetype())
-      interfaceTy = ArchetypeBuilder::mapTypeOutOfContext(DC, type);
+    auto interfaceTy = DC->mapTypeOutOfContext(aliasDecl->getAliasType());
     aliasDecl->setInterfaceType(MetatypeType::get(interfaceTy));
 
     aliasDecl->setImplicit();

stdlib/public/core/Arrays.swift.gyb

@@ -1769,7 +1769,7 @@ extension ${Self} {
   public mutating func replaceSubrange<C>(
     _ subrange: Range<Int>,
     with newElements: C
-  ) where C : Collection, C.Iterator.Element == _Buffer.Element {
+  ) where C : Collection, C.Iterator.Element == Element {
 % if Self in ['Array', 'ContiguousArray']:
     _precondition(subrange.lowerBound >= self._buffer.startIndex,
       "${Self} replace: subrange start is negative")
@@ -2289,7 +2289,7 @@ extension ${Self} {
   public mutating func replaceRange<C>(
     _ subRange: Range<Int>,
     with newElements: C
-  ) where C : Collection, C.Iterator.Element == _Buffer.Element {
+  ) where C : Collection, C.Iterator.Element == Element {
     Builtin.unreachable()
   }
 

test/Sema/accessibility.swift

@@ -637,3 +637,21 @@ internal struct AssocTypeOuterProblem2 {
     fileprivate typealias Assoc = Int // expected-error {{type alias 'Assoc' must be as accessible as its enclosing type because it matches a requirement in protocol 'AssocTypeProto'}} {{5-16=internal}}
   }
 }
+
+// This code was accepted in Swift 3
+public protocol P {
+  associatedtype Element
+
+  func f() -> Element
+}
+
+struct S<T> : P {
+  func f() -> T { while true {} }
+}
+
+public struct G<T> {
+  typealias A = S<T> // expected-note {{type declared here}}
+
+  public func foo<U : P>(u: U) where U.Element == A.Element {}
+  // expected-error@-1 {{instance method cannot be declared public because its generic requirement uses an internal type}}
+}