[Xamarin.Android.Build.Tasks] fix <CilStrip/> for Hybrid AOT

Documentation/release-notes/4818.md

@@ -0,0 +1,5 @@
+#### Application and library build and deployment
+
+  * [GitHub 4818](https://github.com/xamarin/xamarin-android/issues/4818):
+    Applications using `AndroidAotMode=Hybrid` did not properly strip
+    away the IL from the resulting .NET assemblies.

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

@@ -4331,5 +4331,37 @@ public void XA4310 ([Values ("apk", "aab")] string packageFormat)
 
 			}
 		}
+
+		[Test]
+		public void HybridAOT ()
+		{
+			var proj = new XamarinAndroidApplicationProject () {
+				IsRelease = true,
+				AotAssemblies = true,
+			};
+			proj.SetProperty ("AndroidAotMode", "Hybrid");
+			// So we can use Mono.Cecil to open assemblies directly
+			proj.SetProperty ("AndroidEnableAssemblyCompression", "False");
+
+			using (var b = CreateApkBuilder ()) {
+				b.Build (proj);
+
+				var apk = Path.Combine (Root, b.ProjectDirectory, proj.OutputPath, $"{proj.PackageName}.apk");
+				FileAssert.Exists (apk);
+				using (var zip = ZipHelper.OpenZip (apk)) {
+					var entry = zip.ReadEntry ($"assemblies/{proj.ProjectName}.dll");
+					Assert.IsNotNull (entry, $"{proj.ProjectName}.dll should exist in apk!");
+					using (var stream = new MemoryStream ()) {
+						entry.Extract (stream);
+						stream.Position = 0;
+						using (var assembly = AssemblyDefinition.ReadAssembly (stream)) {
+							var type = assembly.MainModule.GetType ($"{proj.ProjectName}.MainActivity");
+							var method = type.Methods.First (m => m.Name == "OnCreate");
+							Assert.LessOrEqual (method.Body.Instructions.Count, 1, "OnCreate should have stripped method bodies!");
+						}
+					}
+				}
+			}
+		}
 	}
 }

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

@@ -929,11 +929,6 @@ public void BuildIncrementalAot (string supportedAbis, string androidAotMode, bo
 					Assert.IsFalse (b.Output.IsTargetSkipped (target), $"`{target}` should *not* be skipped on first build!");
 				}
 
-				if (androidAotMode == "Hybrid") {
-					// FIXME: with Hybrid AOT, <CilStrip/> modifies assemblies in-place
-					Assert.Ignore ("Ignoring, Hybrid AOT triggers _BuildApkEmbed.");
-				}
-
 				b.BuildLogFile = "second.log";
 				b.CleanupAfterSuccessfulBuild = false;
 				b.CleanupOnDispose = false;

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

@@ -2151,13 +2151,17 @@ because xbuild doesn't support framework reference assemblies.
 	   <Output TaskParameter="NativeLibrariesReferences" ItemName="_AdditionalNativeLibraryReferences" />
   </Aot>
 
+  <ItemGroup Condition=" '$(AndroidAotMode)' == 'Hybrid' And '$(AotAssemblies)' == 'True' ">
+    <_CilStripAssemblies Include="@(_ShrunkAssemblies)" Condition=" '%(FileName)' != 'Mono.Android' " />
+  </ItemGroup>
+
   <!-- Strip the IL code of the resolved managed assemblies -->
    <CilStrip
 	Condition=" '$(AndroidAotMode)' == 'Hybrid' And '$(AotAssemblies)' == 'True' "
 	AndroidAotMode="$(AndroidAotMode)"
 	ToolPath="$(_MonoAndroidToolsDirectory)"
 	ApkOutputPath="$(_BuildApkEmbedOutputs)"
-	ResolvedAssemblies="@(_ResolvedAssemblies)">
+	ResolvedAssemblies="@(_CilStripAssemblies)">
   </CilStrip> 
 
   <!-- Bundle the assemblies into native libraries in the apk -->