Enable AccessLevelOnImport by default.

This feature also makes it an error for `.swiftinterface` files to publicly import non-resilient modules, so I've updated our `.swiftinterface` test case to stop depending on Foundation, which is not resilient on Linux.

PiperOrigin-RevId: 640123191

swift/toolchains/xcode_swift_toolchain.bzl

@@ -646,6 +646,13 @@ def _xcode_swift_toolchain_impl(ctx):
         target_triple = target_triple,
     ))
     requested_features.extend(default_warnings_as_errors_features())
+    requested_features.extend([
+        # Allow users to start using access levels on `import`s by default. Note
+        # that this does *not* change the default access level for `import`s to
+        # `internal`; that is controlled by the upcoming feature flag
+        # `InternalImportsByDefault`.
+        "swift.experimental.AccessLevelOnImport",
+    ])
 
     # TODO: b/336996662 - Use a very high Xcode version number until we've
     # confirmed the actual Xcode release that ships with a compiler that

test/fixtures/module_interface/Client.swift

@@ -15,5 +15,5 @@
 import ToyModule
 
 let value = ToyValue(number: 10)
-print(value.hexString)
+print(value.stringValue)
 print(value.squared())

test/fixtures/module_interface/library/ToyModule.swift

@@ -12,17 +12,15 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import Foundation
-
 /// A toy value.
 @frozen
 public struct ToyValue {
   /// The numeric value.
   public var number: Int
 
   /// The hexadecimal value of the numeric value.
-  public var hexString: String {
-    String(format: "0x%x", number)
+  public var stringValue: String {
+    "\(number)"
   }
 
   /// Creates a new toy value with the given numeric value.