add currentTimestamp()

Author: cherylEnkidu

Firestore/Swift/Source/SwiftAPI/Pipeline/Expressions/FunctionExpressions/CurrentTimestamp.swift

@@ -0,0 +1,30 @@
+// Copyright 2024 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
+
+/// An expression that represents a server-side timestamp.
+///
+/// `CurrentTimestamp` is used to generate a timestamp on the server.
+/// This is useful for recording current date and time.
+///
+/// Example:
+/// ```swift
+/// CurrentTimestamp().as("createdAt")
+/// ```
+public class CurrentTimestamp: FunctionExpression, @unchecked Sendable {
+  public init() {
+    super.init("current_timestamp", [])
+  }
+}

Firestore/Swift/Tests/Integration/PipelineTests.swift

@@ -3157,6 +3157,21 @@ class PipelineIntegrationTests: FSTIntegrationTestCase {
     }
   }
 
+  func testCurrentTimestampWorks() async throws {
+    let collRef = collectionRef(withDocuments: ["doc1": ["foo": 1]])
+    let db = collRef.firestore
+
+    let pipeline = db.pipeline()
+      .collection(collRef.path)
+      .select([
+        CurrentTimestamp().as("timestamp"),
+      ])
+
+    let snapshot = try await pipeline.execute()
+
+    XCTAssertEqual(snapshot.results.count, 1)
+  }
+
   func testSupportsByteLength() async throws {
     let db = firestore()
     let randomCol = collectionRef()