[Xamarin.Android.Build.Tasks] <FilterAssemblies/> should look for .jar files

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

@@ -9,20 +9,16 @@
 namespace Xamarin.Android.Tasks
 {
 	/// <summary>
-	/// Filters a set of assemblies based on a given TargetFrameworkIdentifier or FallbackReference
+	/// Filters a set of assemblies to be known as "Xamarin.Android" assemblies through various checks:
+	/// * The presence of [assembly: System.Runtime.Versioning.TargetFramework("MonoAndroid,Version=v9.0")]
+	/// * A Mono.Android.dll reference
+	/// * An EmbeddedResource ending with *.jar
+	/// * An EmbeddedResource beginning with __Android
 	/// </summary>
 	public class FilterAssemblies : Task
 	{
-		/// <summary>
-		/// The MonoAndroid portion of [assembly: System.Runtime.Versioning.TargetFramework("MonoAndroid,v9.0")]
-		/// </summary>
-		[Required]
-		public string TargetFrameworkIdentifier { get; set; }
-
-		/// <summary>
-		/// If TargetFrameworkIdentifier is missing, we can look for Mono.Android.dll references instead
-		/// </summary>
-		public string FallbackReference { get; set; }
+		const string TargetFrameworkIdentifier = "MonoAndroid";
+		const string MonoAndroidReference = "Mono.Android";
 
 		[Required]
 		public bool DesignTimeBuild { get; set; }
@@ -51,23 +47,52 @@ public override bool Execute ()
 						output.Add (assemblyItem);
 						continue;
 					}
-					// Fallback to looking at references
-					if (string.IsNullOrEmpty (targetFrameworkIdentifier) && !string.IsNullOrEmpty (FallbackReference)) {
-						Log.LogDebugMessage ($"Checking references for: {assemblyItem.ItemSpec}");
-						foreach (var handle in reader.AssemblyReferences) {
-							var reference = reader.GetAssemblyReference (handle);
-							var name = reader.GetString (reference.Name);
-							if (FallbackReference == name) {
-								output.Add (assemblyItem);
-								break;
-							}
-						}
+
+					// In the rare case, [assembly: TargetFramework("MonoAndroid,Version=v9.0")] may not match
+					Log.LogDebugMessage ($"{nameof (TargetFrameworkIdentifier)} did not match: {assemblyItem.ItemSpec}");
+
+					// Fallback to looking for a Mono.Android reference
+					if (HasReference (reader)) {
+						Log.LogDebugMessage ($"{MonoAndroidReference} reference found: {assemblyItem.ItemSpec}");
+						output.Add (assemblyItem);
+						continue;
+					}
+					// Fallback to looking for *.jar or __Android EmbeddedResource files
+					if (HasEmbeddedResource (reader)) {
+						Log.LogDebugMessage ($"EmbeddedResource found: {assemblyItem.ItemSpec}");
+						output.Add (assemblyItem);
+						continue;
 					}
 				}
 			}
 			OutputAssemblies = output.ToArray ();
 
 			return !Log.HasLoggedErrors;
 		}
+
+		bool HasReference (MetadataReader reader)
+		{
+			foreach (var handle in reader.AssemblyReferences) {
+				var reference = reader.GetAssemblyReference (handle);
+				var name = reader.GetString (reference.Name);
+				if (MonoAndroidReference == name) {
+					return true;
+				}
+			}
+			return false;
+		}
+
+		bool HasEmbeddedResource (MetadataReader reader)
+		{
+			foreach (var handle in reader.ManifestResources) {
+				var resource = reader.GetManifestResource (handle);
+				var name = reader.GetString (resource.Name);
+				if (name.EndsWith (".jar", StringComparison.OrdinalIgnoreCase) ||
+						name.StartsWith ("__Android", StringComparison.OrdinalIgnoreCase)) {
+					return true;
+				}
+			}
+			return false;
+		}
 	}
 }

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

@@ -3889,6 +3889,30 @@ public void AbiDelimiters ([Values ("armeabi-v7a%3bx86", "armeabi-v7a,x86")] str
 				Assert.IsTrue (b.Build (proj), "Build should have succeeded.");
 			}
 		}
+
+		[Test]
+		public void WorkManager ()
+		{
+			var proj = new XamarinFormsAndroidApplicationProject ();
+			proj.Sources.Add (new BuildItem.Source ("MyWorker.cs") {
+				TextContent = () =>
+@"using System;
+using Android.Content;
+using AndroidX.Work;
+
+public class MyWorker : Worker
+{
+	public MyWorker (Context c, WorkerParameters p) : base (c, p) { }
+
+	public override Result DoWork () => Result.InvokeSuccess ();
+}
+"
+			});
+			proj.PackageReferences.Add (KnownPackages.Android_Arch_Work_Runtime);
+			using (var b = CreateApkBuilder (Path.Combine ("temp", TestName))) {
+				Assert.IsTrue (b.Build (proj), "Build should have succeeded.");
+			}
+		}
 	}
 }
 

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

@@ -65,8 +65,6 @@ string [] Run (params string [] assemblies)
 		{
 			var task = new FilterAssemblies {
 				BuildEngine = new MockBuildEngine (TestContext.Out),
-				TargetFrameworkIdentifier = "MonoAndroid",
-				FallbackReference = "Mono.Android",
 				InputAssemblies = assemblies.Select (a => new TaskItem (a)).ToArray (),
 			};
 			Assert.IsTrue (task.Execute (), "task.Execute() should have succeeded.");
@@ -98,5 +96,16 @@ public async Task XamarinForms ()
 			};
 			CollectionAssert.AreEqual (expected, actual);
 		}
+
+		[Test]
+		public async Task GuavaListenableFuture ()
+		{
+			var assemblies = await GetAssembliesFromNuGet (
+				"https://www.nuget.org/api/v2/package/Xamarin.Google.Guava.ListenableFuture/1.0.0",
+				"lib/MonoAndroid50/");
+			var actual = Run (assemblies);
+			var expected = new [] { "Xamarin.Google.Guava.ListenableFuture.dll" };
+			CollectionAssert.AreEqual (expected, actual);
+		}
 	}
 }

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Android/KnownPackages.cs

@@ -625,6 +625,16 @@ public static class KnownPackages
 				}
 			}
 		};
+		public static Package Android_Arch_Work_Runtime = new Package {
+			Id = "Xamarin.Android.Arch.Work.Runtime",
+			Version = "1.0.0",
+			TargetFramework = "MonoAndroid90",
+			References = {
+				new BuildItem.Reference("Xamarin.Android.Arch.Work.Runtime") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Arch.Work.Runtime.1.0.0\\lib\\MonoAndroid90\\Xamarin.Android.Arch.Work.Runtime.dll"
+				}
+			}
+		};
 		public static Package Xamarin_Android_Crashlytics_2_9_4 = new Package {
 			Id = "Xamarin.Android.Crashlytics",
 			Version = "2.9.4",

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -519,8 +519,6 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
   </ItemGroup>
   <FilterAssemblies
       DesignTimeBuild="$(DesignTimeBuild)"
-      TargetFrameworkIdentifier="MonoAndroid"
-      FallbackReference="Mono.Android"
       InputAssemblies="@(_ReferencePath);@(_ReferenceDependencyPaths)">
     <Output TaskParameter="OutputAssemblies" ItemName="_MonoAndroidReferencePath" />
   </FilterAssemblies>