Add custom SwiftLint rule to prevent missing foundation import to prevent error

Summary:
In D33750740 (8044535803) Hackbook started showing me the following error

```
objc attribute used without importing module 'Foundation'
```

This custom rule should prevent most cases of this. (It will only detect cases in which there are only empty lines between the license and the first objc)

Ran the following to add missing imports
```
git ls-files '*.swift' | xargs perl -0777 -pi -e s'/(of this source tree.\n \*\/)\n+\objc/\1\n\nimport Foundation\n\n\objc/'
```

Reviewed By: samodom

Differential Revision: D33783526

fbshipit-source-id: e75e1a66152d9a9790aa363d2fe7c71fd9446849

.swiftlint.yml

@@ -61,6 +61,9 @@ custom_rules:
   objc_members_above_objc:
     regex: "@objc[^\n]*?\n@objcMembers"
     message: "Place @objcMembers above @objc"
+  objc_used_without_importing_foundation:
+    regex: "LICENSE file in the root directory of this source tree.\n \\*/\n+@objc"
+    message: "@objc attribute used without importing module 'Foundation'"
 
 only_rules:
   - array_init

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/FBSDKLoginManager+Fake.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 @objc(FBSDKLoginManager) // for NSClassFromString(@"FBSDKLoginManager")
 class FBSDKLoginManager: NSObject {

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/SampleEventBinding.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class SampleEventBinding: NSObject {
 

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/SampleRawRemoteEventBindings.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class SampleRawRemoteEventBindings: NSObject {
 

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/ServerConfigurationFixtures.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class ServerConfigurationFixtures: NSObject {
   // swiftlint:disable line_length

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestATEPublisher.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestATEPublisher: NSObject, ATEPublishing {
   var publishATEWasCalled = false

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestATEPublisherFactory.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestATEPublisherFactory: NSObject, ATEPublisherCreating {
   var stubbedPublisher: ATEPublishing? = TestATEPublisher()

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestAccessTokenExpirer.swift

@@ -6,5 +6,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 final class TestAccessTokenExpirer: NSObject, AccessTokenExpiring {}

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestAppEventsConfiguration.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestAppEventsConfiguration: NSObject, AppEventsConfigurationProtocol {
   static var stubbedDefaultConfiguration: TestAppEventsConfiguration?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestAppEventsConfigurationProvider.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestAppEventsConfigurationProvider: NSObject, AppEventsConfigurationProviding {
   var stubbedConfiguration: AppEventsConfigurationProtocol?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestAppEventsReporter.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestAppEventsReporter: NSObject, AppEventsReporter {
   var enableWasCalled = false

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestAppEventsStateProvider.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestAppEventsStateProvider: NSObject, AppEventsStateProviding {
   var state: TestAppEventsState?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestAppEventsStateStore.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestAppEventsStateStore: NSObject, AppEventsStatePersisting {
   var capturedPersistedState: [Any] = []

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestAppLinkResolver.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestAppLinkResolver: NSObject, AppLinkResolving {
   var capturedURL: URL?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestAppStoreReceiptProvider.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestAppStoreReceiptProvider: AppStoreReceiptProviding {
   var wasAppStoreReceiptURLRead = false

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestApplicationDelegateObserver.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestApplicationDelegateObserver: NSObject, FBSDKApplicationObserving {
   var didFinishLaunchingCallCount = 0

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestBackgroundEventLogger.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestBackgroundEventLogger: NSObject, BackgroundEventLogging {
 

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestBridgeAPIResponseFactory.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestBridgeAPIResponseFactory: NSObject, BridgeAPIResponseCreating {
 

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestCodelessEvents.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestCodelessEvents: NSObject, CodelessIndexing {
 

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestDylibResolver.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestDylibResolver: NSObject, FBSDKDynamicFrameworkResolving {
   var stubSafariViewControllerClass: AnyClass?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestErrorConfigurationProvider.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestErrorConfigurationProvider: NSObject, ErrorConfigurationProviding {
   var configuration: ErrorConfigurationProtocol?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestGateKeeperManager.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestGateKeeperManager: NSObject, GateKeeperManaging {
   static var gateKeepers = [String?: Bool]()

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestGraphRequestBody.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestGraphRequestBody: GraphRequestBody {
   var capturedKey: String?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestLogger.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestLogger: Logger {
   static var capturedLoggingBehavior: LoggingBehavior?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestLoggerFactory.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestLoggerFactory: NSObject, LoggerCreating {
   var capturedLoggingBehavior: LoggingBehavior?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestMetadataIndexer.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestMetadataIndexer: NSObject, MetadataIndexing {
   var enableWasCalled = false

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestPaymentObserver.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestPaymentObserver: NSObject, PaymentObserving {
   var didStartObservingTransactions = false

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestTimeSpentRecorder.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestTimeSpentRecorder: NSObject, SourceApplicationTracking, TimeSpentRecording {
 

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestTouch.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestTouch: UITouch {
   var stubbedView: UIView?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestURLSessionProxy.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestURLSessionProxy: NSObject, URLSessionProxying {
   var delegateQueue: OperationQueue?

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestURLSessionProxyFactory.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestURLSessionProxyFactory: NSObject, URLSessionProxyProviding {
   private var stubbedSessions: [TestURLSessionProxy]

FBSDKCoreKit/FBSDKCoreKitTests/Internal/Helpers/TestUserIDProvider.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 class TestUserIDProvider: NSObject, UserIDProviding {
   var userID: String?

FBSDKShareKit/FBSDKShareKitTests/TestInternalURLOpener.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 final class TestInternalURLOpener: NSObject, ShareInternalURLOpening {
   var canOpenURL = false

FBSDKShareKit/FBSDKShareKitTests/TestShareUtility.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 final class TestShareUtility: NSObject, _ShareUtilityProtocol {
   static var stubbedValidateShareShouldThrow = false

TestTools/TestTools/TestBridgeAPIRequest.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 public class TestBridgeAPIRequest: NSObject, BridgeAPIRequestProtocol {
   public var actionID: String

TestTools/TestTools/TestBridgeAPIRequestOpener.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 public class TestBridgeAPIRequestOpener: NSObject, BridgeAPIRequestOpening {
 

TestTools/TestTools/TestErrorFactory.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 public final class TestErrorFactory: NSObject, ErrorCreating {
   public func error(

TestTools/TestTools/TestSDKError.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objc public enum TestSDKErrorType: Int {
   case general
   case invalidArgument

TestTools/TestTools/TestSettings.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 public class TestSettings: NSObject, SettingsProtocol, SettingsLogging {
   public var isEventDataUsageLimited = false

TestTools/TestTools/UserDefaultsSpy.swift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import Foundation
+
 @objcMembers
 public class UserDefaultsSpy: UserDefaults {
   public var capturedObjectRetrievalKeys = [String]()