Sema: Add simulation of buggy Swift 3 typealias accessibility checking

Basically if the underlying type of a typealias was dependent on
generic parameters from context, it wouldn't participate in
accessibility checking.

Turns out people were (accidentally) relying on this behavior, so
add a simulation of it in Swift 3 mode by ignoring such typealiases
entirely.

Fixes <rdar://problem/29549232>.

lib/Sema/TypeCheckDecl.cpp

@@ -1139,6 +1139,7 @@ static void recordSelfContextType(AbstractFunctionDecl *func) {
 namespace {
 
 class AccessScopeChecker {
+  ASTContext &Context;
   const SourceFile *File;
   TypeChecker::TypeAccessScopeCacheMap &Cache;
 
@@ -1147,7 +1148,9 @@ protected:
 
   AccessScopeChecker(const DeclContext *useDC,
                      decltype(TypeChecker::TypeAccessScopeCache) &caches)
-      : File(useDC->getParentSourceFile()), Cache(caches[File]),
+      : Context(useDC->getASTContext()),
+        File(useDC->getParentSourceFile()),
+        Cache(caches[File]),
         Scope(AccessScope::getPublic()) {}
 
   bool visitDecl(ValueDecl *VD) {
@@ -1161,6 +1164,12 @@ protected:
         return true;
     }
 
+    // Simulation for Swift 3 bug.
+    if (isa<TypeAliasDecl>(VD) &&
+        VD->getInterfaceType()->hasTypeParameter() &&
+        Context.isSwiftVersion3())
+      return true;
+
     auto cached = Cache.find(VD);
     if (cached != Cache.end()) {
       Scope = Scope->intersectWith(cached->second);

test/Compatibility/accessibility_typealias.swift

@@ -0,0 +1,42 @@
+// RUN: %target-typecheck-verify-swift -swift-version 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>
+
+  public func foo<U : P>(u: U) where U.Element == A.Element {}
+}
+
+public final class ReplayableGenerator<S: Sequence> : IteratorProtocol {
+    typealias Sequence = S
+    public typealias Element = Sequence.Iterator.Element
+
+    public func next() -> Element? {
+      return nil
+    }
+}
+
+struct Generic<T> {
+  fileprivate typealias Dependent = T
+}
+
+var x: Generic<Int>.Dependent = 3
+
+func internalFuncWithFileprivateAlias() -> Generic<Int>.Dependent {
+  return 3
+}
+
+private func privateFuncWithFileprivateAlias() -> Generic<Int>.Dependent {
+  return 3
+}
+
+var y = privateFuncWithFileprivateAlias()

test/Sema/accessibility.swift

@@ -637,21 +637,3 @@ 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}}
-}

test/Sema/accessibility_private.swift

@@ -210,24 +210,3 @@ fileprivate struct SR2579 {
   private var outerProperty = Inner().innerProperty // expected-warning {{property should not be declared in this context because its type 'SR2579.Inner.InnerPrivateType' uses a private type}}
   var outerProperty2 = Inner().innerProperty // expected-warning {{property should be declared private because its type 'SR2579.Inner.InnerPrivateType' uses a private type}}
 }
-
-// FIXME: Dependent member lookup of typealiases is not subject
-// to accessibility checking.
-struct Generic<T> {
-  fileprivate typealias Dependent = T
-}
-
-var x: Generic<Int>.Dependent = 3
-// expected-error@-1 {{variable must be declared private or fileprivate because its type uses a fileprivate type}}
-
-func internalFuncWithFileprivateAlias() -> Generic<Int>.Dependent {
-// expected-error@-1 {{function must be declared private or fileprivate because its result uses a fileprivate type}}
-  return 3
-}
-
-private func privateFuncWithFileprivateAlias() -> Generic<Int>.Dependent {
-  return 3
-}
-
-// FIXME: No error here
-var y = privateFuncWithFileprivateAlias()

test/Sema/accessibility_typealias.swift

@@ -0,0 +1,46 @@
+// RUN: %target-typecheck-verify-swift -swift-version 4
+
+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}}
+}
+
+public final class ReplayableGenerator<S: Sequence> : IteratorProtocol {
+    typealias Sequence = S // expected-note {{type declared here}}
+    public typealias Element = Sequence.Iterator.Element // expected-error {{type alias cannot be declared public because its underlying type uses an internal type}}
+
+    public func next() -> Element? {
+      return nil
+    }
+}
+
+// FIXME: Dependent member lookup of typealiases is not subject
+// to accessibility checking.
+struct Generic<T> {
+  fileprivate typealias Dependent = T
+}
+
+var x: Generic<Int>.Dependent = 3 // expected-error {{variable must be declared private or fileprivate because its type uses a fileprivate type}}
+
+func internalFuncWithFileprivateAlias() -> Generic<Int>.Dependent { // expected-error {{function must be declared private or fileprivate because its result uses a fileprivate type}}
+  return 3
+}
+
+private func privateFuncWithFileprivateAlias() -> Generic<Int>.Dependent {
+  return 3
+}
+
+// FIXME: No error here
+var y = privateFuncWithFileprivateAlias()