Add "swift" flag to firebaseUserAgent

Example/Core/Tests/FIRAppTest.m

@@ -735,6 +735,10 @@ - (void)testRegisteringNonConformingLibrary {
   XCTAssertFalse([[FIRApp firebaseUserAgent] containsString:@"InvalidLibrary`/1.0.0"]);
 }
 
+- (void)testSwiftFlagWithNoSwift {
+  XCTAssertFalse([[FIRApp firebaseUserAgent] containsString:@"swift"]);
+}
+
 #pragma mark - Core Diagnostics
 
 - (void)testCoreDiagnosticsLoggedWhenFIRAppIsConfigured {

Example/Core/Tests/Swift/FIRAppTests.swift

@@ -0,0 +1,22 @@
+// Copyright 2019 Google
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import XCTest
+@testable import FirebaseCore
+
+class FIRAppTests: XCTestCase {
+  func testSwiftFlagWithSwift() {
+    XCTAssertTrue(FirebaseApp.firebaseUserAgent().contains("swift"))
+  }
+}

Example/Core/Tests/Swift/FirebaseCore-iOS-Unit-swift-unit-Bridging-Header.h

@@ -0,0 +1,15 @@
+// Copyright 2019 Google
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#import "FIRAppInternal.h"

Firebase/Core/FIRApp.m

@@ -35,6 +35,8 @@
 #import "Private/FIROptionsInternal.h"
 #import "Private/FIRVersion.h"
 
+#import <objc/runtime.h>
+
 // The kFIRService strings are only here while transitioning CoreDiagnostics from the Analytics
 // pod to a Core dependency. These symbols are not used and should be deleted after the transition.
 NSString *const kFIRServiceAdMob;
@@ -537,7 +539,13 @@ + (NSString *)firebaseUserAgent {
       if (sdkVersion) {
         [FIRApp registerLibrary:@"apple-sdk" withVersion:sdkVersion];
       }
+
+      if ([self hasSwiftRuntime]) {
+        // Add "swift" flag to the `firebaseUserAgent`.
+        [FIRApp registerLibrary:@"swift" withVersion:@"true"];
+      }
     });
+
     NSMutableArray<NSString *> *libraries =
         [[NSMutableArray<NSString *> alloc] initWithCapacity:sLibraryVersions.count];
     for (NSString *libraryName in sLibraryVersions) {
@@ -549,6 +557,10 @@ + (NSString *)firebaseUserAgent {
   }
 }
 
++ (BOOL)hasSwiftRuntime {
+  return objc_lookUpClass("Swift._SwiftObject") != nil;
+}
+
 - (void)checkExpectedBundleID {
   NSArray *bundles = [FIRBundleUtil relevantBundles];
   NSString *expectedBundleID = [self expectedBundleID];

FirebaseCore.podspec

@@ -48,4 +48,12 @@ Firebase Core includes FIRApp and FIROptions which provide central configuration
     unit_tests.dependency 'OCMock'
     unit_tests.resources = 'Example/Core/App/GoogleService-Info.plist'
   end
+
+  s.test_spec 'swift-unit' do |swift_unit_tests|
+    swift_unit_tests.source_files = 'Example/Core/Tests/Swift/**/*.swift',
+                                    'Example/Core/Tests/Swift/**/*.h'
+    swift_unit_tests.pod_target_xcconfig = {
+      'SWIFT_OBJC_BRIDGING_HEADER' => '$(PODS_ROOT)/../../Example/Core/Tests/Swift/FirebaseCore-iOS-Unit-swift-unit-Bridging-Header.h'
+    }
+  end
 end