Require explicit typing for DocumentSnapshot decoding. DocumentReference decoding.

Firestore/Swift/Source/Codable/DocumentReference+ReadDecodable.swift

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2021 Google LLC
+ *
+ * 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 Foundation
+import FirebaseFirestore
+
+public extension DocumentReference {
+  /// Fetches and decodes the document referenced by this `DocumentReference`.
+  ///
+  /// This allows users to retrieve a Firestore document and have it decoded to an instance of
+  /// caller-specified type as follows:
+  /// ```swift
+  /// ref.getDocument(as: Book.self) { result in
+  ///   do {
+  ///     let book = try result.get()
+  ///   } catch {
+  ///     // Handle error
+  ///   }
+  /// }
+  /// ```
+  /// - Parameters:
+  ///   - as: A `Decodable` type to convert the document fields to.
+  ///   - serverTimestampBehavior: Configures how server timestamps that have
+  ///     not yet been set to their final value are returned from the snapshot.
+  ///   - decoder: The decoder to use to convert the document. Defaults to use
+  ///     default decoder.
+  ///   - completion: The closure to call when the document snapshot has been fetched and decoded.
+  func getDocument<T: Decodable>(as type: T.Type,
+                                 with serverTimestampBehavior: ServerTimestampBehavior =
+                                   .none,
+                                 decoder: Firestore.Decoder = .init(),
+                                 completion: @escaping (Result<T, Error>) -> Void) {
+    getDocument { snapshot, error in
+      guard let snapshot = snapshot else {
+        /**
+         * Force unwrapping here is fine since this logic corresponds to the auto-synthesized
+         * async/await wrappers for Objective-C functions with callbacks taking an object and an error
+         * parameter. The API should (and does) guarantee that either object or error is set, but never both.
+         * For more details see:
+         * https://github.com/firebase/firebase-ios-sdk/pull/9101#discussion_r809117034
+         */
+        completion(.failure(error!))
+        return
+      }
+      let result = Result {
+        try snapshot.data(as: T.self,
+                          with: serverTimestampBehavior,
+                          decoder: decoder)
+      }
+      completion(result)
+    }
+  }
+
+  #if compiler(>=5.5) && canImport(_Concurrency)
+    /// Fetches and decodes the document referenced by this `DocumentReference`.
+    ///
+    /// This allows users to retrieve a Firestore document and have it decoded to an instance of
+    /// caller-specified type.
+    /// ```swift
+    /// do {
+    ///   let book = try await ref.getDocument(as: Book.self)
+    /// } catch {
+    ///   // Handle error
+    /// }
+    /// ```
+    /// - Parameters:
+    ///   - as: A `Decodable` type to convert the document fields to.
+    ///   - serverTimestampBehavior: Configures how server timestamps that have
+    ///     not yet been set to their final value are returned from the snapshot.
+    ///   - decoder: The decoder to use to convert the document. Defaults to use
+    ///     default decoder.
+    /// - Returns: This instance of the supplied `Decodable` type `T`.
+    @available(iOS 15, tvOS 15, macOS 12, watchOS 8, *)
+    func getDocument<T: Decodable>(as type: T.Type,
+                                   with serverTimestampBehavior: ServerTimestampBehavior =
+                                     .none,
+                                   decoder: Firestore.Decoder = .init()) async throws -> T {
+      let snapshot = try await getDocument()
+      return try snapshot.data(as: T.self,
+                               with: serverTimestampBehavior,
+                               decoder: decoder)
+    }
+  #endif
+}

Firestore/Swift/Source/Codable/DocumentReference+WriteEncodable.swift

@@ -27,8 +27,8 @@ public extension DocumentReference {
   /// - Parameters:
   ///   - value: An instance of `Encodable` to be encoded to a document.
   ///   - encoder: An encoder instance to use to run the encoding.
-  ///   - completion: A block to execute once the document has been successfully
-  ///                 written to the server. This block will not be called while
+  ///   - completion: A closure to execute once the document has been successfully
+  ///                 written to the server. This closure will not be called while
   ///                 the client is offline, though local changes will be visible
   ///                 immediately.
   func setData<T: Encodable>(from value: T,
@@ -49,8 +49,8 @@ public extension DocumentReference {
   ///   - merge: Whether to merge the provided `Encodable` into any existing
   ///            document.
   ///   - encoder: An encoder instance to use to run the encoding.
-  ///   - completion: A block to execute once the document has been successfully
-  ///                 written to the server. This block will not be called while
+  ///   - completion: A closure to execute once the document has been successfully
+  ///                 written to the server. This closure will not be called while
   ///                 the client is offline, though local changes will be visible
   ///                 immediately.
   func setData<T: Encodable>(from value: T,
@@ -76,8 +76,8 @@ public extension DocumentReference {
   ///                  merge. Fields can contain dots to reference nested fields within the
   ///                  document.
   ///   - encoder: An encoder instance to use to run the encoding.
-  ///   - completion: A block to execute once the document has been successfully
-  ///                 written to the server. This block will not be called while
+  ///   - completion: A closure to execute once the document has been successfully
+  ///                 written to the server. This closure will not be called while
   ///                 the client is offline, though local changes will be visible
   ///                 immediately.
   func setData<T: Encodable>(from value: T,

Firestore/Swift/Source/Codable/DocumentSnapshot+ReadDecodable.swift

@@ -19,27 +19,24 @@ import FirebaseFirestore
 
 public extension DocumentSnapshot {
   /// Retrieves all fields in a document and converts them to an instance of
-  /// caller-specified type. Returns `nil` if the document does not exist.
+  /// caller-specified type.
   ///
   /// By default, server-provided timestamps that have not yet been set to their
   /// final value will be returned as `NSNull`. Pass `serverTimestampBehavior`
-  /// configure this behavior.
+  /// to configure this behavior.
   ///
   /// See `Firestore.Decoder` for more details about the decoding process.
   ///
   /// - Parameters
   ///   - type: The type to convert the document fields to.
   ///   - serverTimestampBehavior: Configures how server timestamps that have
   ///     not yet been set to their final value are returned from the snapshot.
-  ///   - decoder: The decoder to use to convert the document. `nil` to use
-  ///     default decoder.
+  ///   - decoder: The decoder to use to convert the document. Defaults to use
+  ///     the default decoder.
   func data<T: Decodable>(as type: T.Type,
                           with serverTimestampBehavior: ServerTimestampBehavior = .none,
-                          decoder: Firestore.Decoder? = nil) throws -> T? {
-    let d = decoder ?? Firestore.Decoder()
-    if let data = data(with: serverTimestampBehavior) {
-      return try d.decode(T.self, from: data, in: reference)
-    }
-    return nil
+                          decoder: Firestore.Decoder = .init()) throws -> T {
+    let data: Any = data(with: serverTimestampBehavior) ?? NSNull()
+    return try decoder.decode(T.self, from: data, in: reference)
   }
 }

Firestore/third_party/FirestoreEncoder/FirestoreDecoder.swift

@@ -38,7 +38,7 @@ public extension Firestore {
     ///             decoded.
     /// - Returns: An instance of specified type by the first parameter.
     public func decode<T: Decodable>(_: T.Type,
-                                     from container: [String: Any],
+                                     from container: Any,
                                      in document: DocumentReference? = nil) throws -> T {
       let decoder = _FirestoreDecoder(referencing: container)
       if let doc = document {