[TrimmableTypeMap] Fix stale legacy JCW contamination when switching typemap flavors

src/Mono.Android/Android.Runtime/JNIEnvInit.cs

@@ -178,9 +178,7 @@ internal static unsafe void Initialize (JnienvInitializeArgs* args)
 
 			args->propagateUncaughtExceptionFn = (IntPtr)(delegate* unmanaged<IntPtr, IntPtr, IntPtr, void>)&PropagateUncaughtException;
 
-			if (!RuntimeFeature.TrimmableTypeMap) {
-				args->registerJniNativesFn = (IntPtr)(delegate* unmanaged<IntPtr, int, IntPtr, IntPtr, int, void>)&RegisterJniNatives;
-			}
+			args->registerJniNativesFn = (IntPtr)(delegate* unmanaged<IntPtr, int, IntPtr, IntPtr, int, void>)&RegisterJniNatives;
 			RunStartupHooksIfNeeded ();
 			SetSynchronizationContext ();
 		}

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.targets

@@ -14,7 +14,6 @@
     <_TypeMapBaseOutputDir>$(IntermediateOutputPath)</_TypeMapBaseOutputDir>
     <_TypeMapBaseOutputDir>$(_TypeMapBaseOutputDir.Replace('\','/'))</_TypeMapBaseOutputDir>
     <_TypeMapOutputDirectory>$(_TypeMapBaseOutputDir)typemap/</_TypeMapOutputDirectory>
-    <_TypeMapJavaOutputDirectory>$(_TypeMapBaseOutputDir)typemap/java</_TypeMapJavaOutputDirectory>
   </PropertyGroup>
 
   <ItemGroup>
@@ -55,7 +54,7 @@
     <GenerateTrimmableTypeMap
         ResolvedAssemblies="@(_TypeMapInputAssemblies)"
         OutputDirectory="$(_TypeMapOutputDirectory)"
-        JavaSourceOutputDirectory="$(_TypeMapJavaOutputDirectory)"
+        JavaSourceOutputDirectory="$(_AndroidIntermediateJavaSourceDirectory)"
         TargetFrameworkVersion="$(TargetFrameworkVersion)"
         ManifestTemplate="$(_AndroidManifestAbs)"
         MergedAndroidManifestOutput="$(_TypeMapBaseOutputDir)AndroidManifest.xml"
@@ -99,15 +98,6 @@
       Inputs="@(_GenerateJavaStubsInputs)"
       Outputs="$(_AndroidStampDirectory)_GenerateJavaStubs.stamp">
 
-    <ItemGroup>
-      <_TypeMapJavaFiles Include="$(_TypeMapJavaOutputDirectory)/**/*.java" />
-    </ItemGroup>
-    <Copy SourceFiles="@(_TypeMapJavaFiles)" DestinationFolder="$(IntermediateOutputPath)android/src/%(RecursiveDir)" />
-
-    <ItemGroup>
-      <FileWrites Include="@(_TypeMapJavaFiles->'$(IntermediateOutputPath)android/src/%(RecursiveDir)%(Filename)%(Extension)')" />
-    </ItemGroup>
-
     <!-- Set properties for ABI/RID used by CoreCLR _AddTrimmableTypeMapAssembliesToStore fallback -->
     <PropertyGroup>
       <_TypeMapFirstAbi Condition=" '$(AndroidSupportedAbis)' != '' ">$([System.String]::Copy('$(AndroidSupportedAbis)').Split(';')[0])</_TypeMapFirstAbi>

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

@@ -845,6 +845,50 @@ public void BuildAfterUpgradingNuget ([Values] AndroidRuntime runtime)
 			}
 		}
 
+		[Test]
+		[NonParallelizable]
+		public void SwitchingTypeMapImplementationTriggersClean ()
+		{
+			var proj = new XamarinAndroidApplicationProject ();
+			proj.SetRuntime (AndroidRuntime.CoreCLR);
+
+			using (var b = CreateApkBuilder ()) {
+				b.CleanupAfterSuccessfulBuild = b.CleanupOnDispose = false;
+				b.Verbosity = LoggerVerbosity.Detailed;
+
+				var projectDir = Path.Combine (Root, b.ProjectDirectory);
+				if (Directory.Exists (projectDir))
+					Directory.Delete (projectDir, true);
+
+				// First build with default (llvm-ir) typemap
+				Assert.IsTrue (b.Build (proj), "first build should have succeeded.");
+				string build_props = b.Output.GetIntermediaryPath ("build.props");
+				FileAssert.Exists (build_props, "build.props should exist after first build.");
+				var firstBuildProps = File.ReadAllText (build_props);
+				Assert.IsTrue (firstBuildProps.Contains ("_androidtypemapimplementation="),
+					"build.props should contain _AndroidTypeMapImplementation.");
+
+				// Second build with trimmable typemap — should trigger clean
+				proj.SetProperty ("_AndroidTypeMapImplementation", "trimmable");
+				b.Save (proj, doNotCleanupOnUpdate: true);
+				Assert.IsTrue (b.Build (proj), "second build (trimmable) should have succeeded.");
+				Assert.IsFalse (b.Output.IsTargetSkipped ("_CleanIntermediateIfNeeded"),
+					"Switching _AndroidTypeMapImplementation should trigger _CleanIntermediateIfNeeded.");
+
+				// Third build switching back to llvm-ir — should trigger clean again
+				proj.SetProperty ("_AndroidTypeMapImplementation", "llvm-ir");
+				b.Save (proj, doNotCleanupOnUpdate: true);
+				Assert.IsTrue (b.Build (proj), "third build (llvm-ir) should have succeeded.");
+				Assert.IsFalse (b.Output.IsTargetSkipped ("_CleanIntermediateIfNeeded"),
+					"Switching _AndroidTypeMapImplementation back should trigger _CleanIntermediateIfNeeded.");
+
+				// Fourth build with no changes — should NOT trigger clean
+				Assert.IsTrue (b.Build (proj), "fourth build (no changes) should have succeeded.");
+				Assert.IsTrue (b.Output.IsTargetSkipped ("_CleanIntermediateIfNeeded"),
+					"A build with no implementation change should skip _CleanIntermediateIfNeeded.");
+			}
+		}
+
 		[Test]
 		[Category ("SmokeTests")]
 		public void BuildInDesignTimeMode (

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

@@ -981,6 +981,7 @@ because xbuild doesn't support framework reference assemblies.
 		<_PropertyCacheItems Include="AndroidManifestPlaceholders=$(AndroidManifestPlaceholders)" />
 		<_PropertyCacheItems Include="ProjectFullPath=$(MSBuildProjectFullPath)" />
 		<_PropertyCacheItems Include="AndroidUseDesignerAssembly=$(AndroidUseDesignerAssembly)" />
+		<_PropertyCacheItems Include="_AndroidTypeMapImplementation=$(_AndroidTypeMapImplementation)" />
 	</ItemGroup>
 	<WriteLinesToFile
 			File="$(_AndroidBuildPropertiesCache)"

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/JcwJavaSourceGeneratorTests.cs

@@ -134,6 +134,17 @@ public void Generate_AcwType_HasRegisterNativesStaticBlock ()
 			AssertContainsLine ("mono.android.Runtime.registerNatives (MainActivity.class);\n", java);
 		}
 
+		[Fact]
+		public void Generate_AcwType_NeverCallsRuntimeRegister ()
+		{
+			var java = GenerateFixture ("my/app/MainActivity");
+			// Trimmable JCWs must call Runtime.registerNatives(klass) and avoid
+			// the legacy Runtime.register(typeName, klass, methods) path, which
+			// relies on reflection-based callback registration and breaks trimming.
+			AssertContainsLine ("mono.android.Runtime.registerNatives (MainActivity.class);\n", java);
+			Assert.DoesNotContain ("Runtime.register (\"", java);
+		}
+
 		[Fact]
 		public void Generate_ApplicationType_SkipsRegisterNatives ()
 		{