[SE-0258] Escalate access of wrapperValue-produced $x to internal.

(cherry picked from commit 1160017)

Author: DougGregor

lib/Sema/CodeSynthesis.cpp

@@ -1523,9 +1523,15 @@ static VarDecl *synthesizePropertyWrapperStorageWrapperProperty(
   addMemberToContextIfNeeded(pbd, dc, var);
   pbd->setStatic(var->isStatic());
 
-  // The property is always private.
-  property->overwriteAccess(AccessLevel::Private);
-  property->overwriteSetterAccess(AccessLevel::Private);
+  // Determine the access level for the property.
+  AccessLevel access =
+    std::min(AccessLevel::Internal, var->getFormalAccess());
+  property->overwriteAccess(access);
+
+  // Determine setter access.
+  AccessLevel setterAccess =
+    std::min(AccessLevel::Internal, var->getSetterFormalAccess());
+  property->overwriteSetterAccess(setterAccess);
 
   // Add the accessors we need.
   bool hasSetter = wrapperVar->isSettable(nullptr) &&

test/SILGen/property_wrappers.swift

@@ -191,14 +191,10 @@ struct WrapperWithStorageValue<T> {
 
 struct UseWrapperWithStorageValue {
   // UseWrapperWithStorageValue.$x.getter
-  // CHECK-LABEL: sil private [ossa] @$s17property_wrappers26UseWrapperWithStorageValueV2$x33_{{.*}}SiGvg : $@convention(method) (UseWrapperWithStorageValue) -> Wrapper<Int>
+  // CHECK-LABEL: sil hidden [transparent] [ossa] @$s17property_wrappers26UseWrapperWithStorageValueV2$xAA0D0VySiGvg : $@convention(method) (UseWrapperWithStorageValue) -> Wrapper<Int>
   // CHECK-NOT: return
   // CHECK: function_ref @$s17property_wrappers23WrapperWithStorageValueV07wrapperF0AA0C0VyxGvg
   @WrapperWithStorageValue(value: 17) var x: Int
-
-  func foo() {
-    _ = $x
-  }
 }
 
 @propertyWrapper

test/decl/var/property_wrappers.swift

@@ -695,7 +695,6 @@ extension Wrapper {
 
 struct TestStorageRef {
   @WrapperWithStorageRef var x: Int // expected-note{{'$$x' declared here}}
-  // expected-note@-1{{'$x' declared here}}
 
   init(x: Int) {
     self.$$x = WrapperWithStorageRef(wrappedValue: x)
@@ -713,10 +712,25 @@ struct TestStorageRef {
 }
 
 func testStorageRef(tsr: TestStorageRef) {
-  let _: Wrapper = tsr.$x // expected-error{{'$x' is inaccessible due to 'private' protection level}}
+  let _: Wrapper = tsr.$x
   _ = tsr.$$x // expected-error{{'$$x' is inaccessible due to 'private' protection level}}
 }
 
+struct TestStorageRefPrivate {
+  @WrapperWithStorageRef private(set) var x: Int
+
+  init() {
+    self.$$x = WrapperWithStorageRef(wrappedValue: 5)
+  }
+}
+
+func testStorageRefPrivate() {
+  var tsr = TestStorageRefPrivate()
+  let a = tsr.$x // okay, getter is internal
+  tsr.$x = a  // expected-error{{cannot assign to property: '$x' is immutable}}
+}
+
+
 // rdar://problem/50873275 - crash when using wrapper with wrapperValue in
 // generic type.
 @propertyWrapper