Fix BuildArchive updates for existing jar entries

src/Xamarin.Android.Build.Tasks/Tasks/BuildArchive.cs

@@ -158,16 +158,26 @@ public override bool RunTask ()
 				// ItemSpec for these will be "<jarfile>#<entrypath>
 				// eg: "obj/myjar.jar#myfile.txt"
 				var jar_file_path = disk_path.Substring (0, disk_path.Length - (jar_entry_name.Length + 1));
-
-				if (apk.ContainsEntry (apk_path)) {
-					Log.LogDebugMessage ("Failed to add jar entry {0} from {1}: the same file already exists in the apk", jar_entry_name, Path.GetFileName (jar_file_path));
-					continue;
-				}
+				var wasExistingOutputEntry = existingEntries.Remove (apk_path);
 
 				using (var stream = File.OpenRead (jar_file_path))
 				using (var jar = ZipArchive.Open (stream)) {
 					var jar_item = jar.ReadEntry (jar_entry_name);
 
+					if (apk.ContainsEntry (apk_path)) {
+						if (!wasExistingOutputEntry) {
+							Log.LogDebugMessage ("Failed to add jar entry {0} from {1}: the same file already exists in the apk", jar_entry_name, Path.GetFileName (jar_file_path));
+							continue;
+						}
+
+						if (apk.GetEntry (apk_path).CRC == jar_item.CRC) {
+							Log.LogDebugMessage ("Skipping {0} from {1} as it is up to date.", jar_entry_name, jar_file_path);
+							continue;
+						}
+
+						apk.DeleteEntry (apk_path);
+					}
+
 					byte [] data;
 					var d = MemoryStreamPool.Shared.Rent ();
 

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/BuildArchiveTests.cs

@@ -0,0 +1,96 @@
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+using NUnit.Framework;
+using Xamarin.Android.Tasks;
+using Xamarin.Tools.Zip;
+
+namespace Xamarin.Android.Build.Tests
+{
+	[TestFixture]
+	public class BuildArchiveTests
+	{
+		string tempDirectory;
+
+		[SetUp]
+		public void Setup ()
+		{
+			tempDirectory = Path.Combine (Path.GetTempPath (), Path.GetRandomFileName ());
+			Directory.CreateDirectory (tempDirectory);
+		}
+
+		[TearDown]
+		public void TearDown ()
+		{
+			Directory.Delete (tempDirectory, recursive: true);
+		}
+
+		[Test]
+		public void ExistingJavaArchiveEntriesAreUpdated ()
+		{
+			var apk = Path.Combine (tempDirectory, "app.apk");
+			var jar = Path.Combine (tempDirectory, "classes.jar");
+
+			CreateArchive (apk, ("commonMain/default/manifest", "existing"), ("stale.txt", "stale"));
+			CreateArchive (jar, ("commonMain/default/manifest", "current"));
+
+			var item = new TaskItem ($"{jar}#commonMain/default/manifest");
+			item.SetMetadata ("ArchivePath", "commonMain/default/manifest");
+			item.SetMetadata ("JavaArchiveEntry", "commonMain/default/manifest");
+
+			var task = new BuildArchive {
+				BuildEngine = new MockBuildEngine (TestContext.Out),
+				ApkOutputPath = apk,
+				FilesToAddToArchive = new ITaskItem [] { item },
+			};
+
+			Assert.IsTrue (task.RunTask (), "task should have succeeded");
+
+			using (var archive = ZipArchive.Open (apk, FileMode.Open)) {
+				archive.AssertEntryContents (apk, "commonMain/default/manifest", "current");
+				archive.AssertDoesNotContainEntry (apk, "stale.txt");
+			}
+		}
+
+		[Test]
+		public void ExistingJavaArchiveEntriesAreSkippedWhenUpToDate ()
+		{
+			var apk = Path.Combine (tempDirectory, "app.apk");
+			var jar = Path.Combine (tempDirectory, "classes.jar");
+
+			CreateArchive (apk, ("commonMain/default/manifest", "current"));
+			CreateArchive (jar, ("commonMain/default/manifest", "current"));
+
+			var item = new TaskItem ($"{jar}#commonMain/default/manifest");
+			item.SetMetadata ("ArchivePath", "commonMain/default/manifest");
+			item.SetMetadata ("JavaArchiveEntry", "commonMain/default/manifest");
+			var messages = new List<BuildMessageEventArgs> ();
+
+			var task = new BuildArchive {
+				BuildEngine = new MockBuildEngine (TestContext.Out, messages: messages),
+				ApkOutputPath = apk,
+				FilesToAddToArchive = new ITaskItem [] { item },
+			};
+
+			Assert.IsTrue (task.RunTask (), "task should have succeeded");
+
+			Assert.That (messages, Has.Some.Property (nameof (BuildMessageEventArgs.Message)).EqualTo ($"Skipping commonMain/default/manifest from {jar} as it is up to date."));
+
+			using (var archive = ZipArchive.Open (apk, FileMode.Open)) {
+				archive.AssertEntryContents (apk, "commonMain/default/manifest", "current");
+			}
+		}
+
+		static void CreateArchive (string path, params (string name, string contents) [] entries)
+		{
+			using (var stream = File.Create (path))
+			using (var archive = ZipArchive.Create (stream)) {
+				foreach (var entry in entries) {
+					archive.AddEntry (entry.name, entry.contents, encoding: Encoding.UTF8);
+				}
+			}
+		}
+	}
+}