Make instanceForProtocol:inContainer: return nullable T (#12391)

Author: andrewheard

FirebaseCore/Extension/FIRComponentType.h

@@ -27,7 +27,8 @@ NS_SWIFT_NAME(ComponentType)
 
 /// Do not use directly. A factory method to retrieve an instance that provides a specific
 /// functionality.
-+ (T)instanceForProtocol:(Protocol *)protocol inContainer:(FIRComponentContainer *)container;
++ (nullable T)instanceForProtocol:(Protocol *)protocol
+                      inContainer:(FIRComponentContainer *)container;
 
 @end
 

FirebaseCore/Sources/FIRComponentType.m

@@ -20,7 +20,8 @@
 
 @implementation FIRComponentType
 
-+ (id)instanceForProtocol:(Protocol *)protocol inContainer:(FIRComponentContainer *)container {
++ (nullable id)instanceForProtocol:(Protocol *)protocol
+                       inContainer:(FIRComponentContainer *)container {
   // Forward the call to the container.
   return [container instanceForProtocol:protocol];
 }

FirebaseStorage/Sources/Storage.swift

@@ -61,8 +61,10 @@ import FirebaseCore
   /// - Parameter app: The custom `FirebaseApp` used for initialization.
   /// - Returns: A `Storage` instance, configured with the custom `FirebaseApp`.
   @objc(storageForApp:) open class func storage(app: FirebaseApp) -> Storage {
-    let provider = ComponentType<StorageProvider>.instance(for: StorageProvider.self,
-                                                           in: app.container)
+    guard let provider = ComponentType<StorageProvider>.instance(for: StorageProvider.self,
+                                                                 in: app.container) else {
+      fatalError("No \(StorageProvider.self) instance found for Firebase app: \(app.name)")
+    }
     return provider.storage(for: Storage.bucket(for: app))
   }
 
@@ -75,8 +77,10 @@ import FirebaseCore
   /// URL.
   @objc(storageForApp:URL:)
   open class func storage(app: FirebaseApp, url: String) -> Storage {
-    let provider = ComponentType<StorageProvider>.instance(for: StorageProvider.self,
-                                                           in: app.container)
+    guard let provider = ComponentType<StorageProvider>.instance(for: StorageProvider.self,
+                                                                 in: app.container) else {
+      fatalError("No \(StorageProvider.self) instance found for Firebase app: \(app.name)")
+    }
     return provider.storage(for: Storage.bucket(for: app, urlString: url))
   }
 

FirebaseStorage/Tests/Unit/StorageComponentTests.swift

@@ -70,14 +70,14 @@ class StorageComponentTests: StorageTestHelpers {
                                                            in: container)
     XCTAssertNotNil(provider)
 
-    let storage1 = provider.storage(for: "randomBucket")
-    let storage2 = provider.storage(for: "randomBucket")
+    let storage1 = provider?.storage(for: "randomBucket")
+    let storage2 = provider?.storage(for: "randomBucket")
     XCTAssertNotNil(storage1)
 
     // Ensure they're the same instance.
     XCTAssert(storage1 === storage2)
 
-    let storage3 = provider.storage(for: "differentBucket")
+    let storage3 = provider?.storage(for: "differentBucket")
     XCTAssertNotNil(storage3)
 
     XCTAssert(storage1 !== storage3)