[dotnet] Fix latent trimmable-static registrar bugs on non-NativeAOT runtimes

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -554,6 +554,9 @@
 					- NativeAOT supported platforms in all configurations
 					- ios/tvos device builds in all configurations
 					- macOS/MacCatalyst builds in release configuration
+				  (On .NET 11+ NativeAOT defaults to 'trimmable-static' instead - that's set earlier, at
+				  evaluation time, in Xamarin.Shared.Sdk.props. The trimmable-static registrar is only smaller
+				  under NativeAOT, so the other runtimes keep managed-static.)
 				- Set 'partial-static' for:
 					- when no assemblies are trimmed and when MarshalManagedExceptionMode is default (or not set)
 				- Otherwise set 'dynamic' 
@@ -601,6 +604,21 @@
 		<ItemGroup Condition="'$(_DynamicRegistrationSupported)' != ''">
 			<RuntimeHostConfigurationOption Include="ObjCRuntime.Runtime.DynamicRegistrationSupported" Value="$(_DynamicRegistrationSupported)" Trim="true" />
 		</ItemGroup>
+		<!--
+			When using the trimmable static registrar together with PrepareAssemblies, we can tell the trimmer to
+			remove the [ProtocolMember] attributes. This makes it possible to trim away types that are only
+			referenced from these attributes (such as generic types in optional protocol members).
+			The assembly-preparer's post-processing pass still needs these attributes (it runs the registrar again
+			after the trimmer), so it reads them from the pre-trim (prepared) assemblies instead.
+			Only do this when the dynamic registrar has been removed (DynamicRegistrationSupported == false): the
+			dynamic registrar reads these attributes via reflection at runtime, so they must be kept when it's
+			present (otherwise the trimmer errors out with IL2045). This is computed here, and not in
+			_ComputeLinkerInputs, because _DynamicRegistrationSupported isn't known until this target has run.
+			See src/TrimAttributes.LinkDescription.xml and tools/assembly-preparer/AssemblyPreparer.cs.
+		-->
+		<ItemGroup Condition="'$(Registrar)' == 'trimmable-static' And '$(_DynamicRegistrationSupported)' == 'false'">
+			<RuntimeHostConfigurationOption Include="ObjCRuntime.TrimProtocolMemberAttributes" Value="true" Trim="true" />
+		</ItemGroup>
 	</Target>
 
 	<!--
@@ -876,15 +894,6 @@
 			<RuntimeHostConfigurationOption Include="ObjCRuntime.Runtime.Arch.IsSimulator" Value="$(_IsSimulatorFeature)" Trim="true" />
 			<RuntimeHostConfigurationOption Include="ObjCRuntime.Runtime.IsManagedStaticRegistrar" Value="$(_IsManagedStaticRegistrarFeature)" Trim="true" />
 			<RuntimeHostConfigurationOption Include="ObjCRuntime.Runtime.IsTrimmableStaticRegistrar" Value="$(_IsTrimmableStaticRegistrarFeature)" Trim="true" />
-			<!--
-				When using the trimmable static registrar together with PrepareAssemblies, we can tell the trimmer to
-				remove the [ProtocolMember] attributes. This makes it possible to trim away types that are only
-				referenced from these attributes (such as generic types in optional protocol members).
-				The assembly-preparer's post-processing pass still needs these attributes (it runs the registrar again
-				after the trimmer), so it reads them from the pre-trim (prepared) assemblies instead.
-				See src/TrimAttributes.LinkDescription.xml and tools/assembly-preparer/AssemblyPreparer.cs.
-			-->
-			<RuntimeHostConfigurationOption Include="ObjCRuntime.TrimProtocolMemberAttributes" Value="true" Trim="true" Condition="'$(Registrar)' == 'trimmable-static' And '$(PrepareAssemblies)' == 'true'" />
 			<RuntimeHostConfigurationOption Include="ObjCRuntime.Runtime.IsNativeAOT" Value="$(_IsNativeAOTFeature)" Trim="true" />
 			<RuntimeHostConfigurationOption Include="ObjCRuntime.Runtime.IsCoreCLR" Value="true" Trim="true" Condition="'$(UseMonoRuntime)' != 'true'" />
 			<RuntimeHostConfigurationOption Include="ObjCRuntime.Runtime.IsCoreCLR" Value="false" Trim="true" Condition="'$(UseMonoRuntime)' == 'true'" />
@@ -1214,6 +1223,14 @@
 				<OutputPath>$(_StrippedAssemblyDirectory)\%(ResolvedFileToPublish.OriginalRelativePath)</OutputPath>
 			</_AssembliesToBeStripped>
 
+			<!-- Some assemblies added to ResolvedFileToPublish don't have OriginalRelativePath set (e.g. the
+			     TypeMap assemblies the trimmable-static registrar generates). Without it the OutputPath above
+			     collapses to the bare stripped directory, and ILStrip fails trying to write to a directory
+			     ("Access to the path '.../stripped/' is denied"). Fall back to the file name in that case. -->
+			<_AssembliesToBeStripped Condition="'%(_AssembliesToBeStripped.OriginalRelativePath)' == ''">
+				<OutputPath>$(_StrippedAssemblyDirectory)\%(Filename)%(Extension)</OutputPath>
+			</_AssembliesToBeStripped>
+
 			<!-- Use forward slashes in OutputPath, otherwise ILStrip will create filenames that resemble the part of
 				 the relative path of the item that uses backslashes, instead of writing the file to the location of the
 				 relative path. -->

tests/linker/link all/LinkAllTest.cs

@@ -508,6 +508,12 @@ public void LinkedAwayGenericTypeAsOptionalMemberInProtocol ()
 			if (!global::XamarinTests.ObjCRuntime.Registrar.IsTrimmableStaticRegistrar)
 				Assert.Ignore ("This test only applies to the trimmable static registrar.");
 
+			// The [ProtocolMember] attributes (which reference NSSet<T>) are only trimmed away when the dynamic
+			// registrar has been removed - it reads these attributes via reflection at runtime, so they're kept
+			// when it's present. Without trimming the attributes, NSSet<T> stays too, so there's nothing to verify.
+			if (global::ObjCRuntime.Runtime.DynamicRegistrationSupported)
+				Assert.Ignore ("This test only applies when the dynamic registrar has been removed.");
+
 			// https://github.com/dotnet/macios/issues/3523
 			// Don't use constants here, because the linker can see what we're trying to do and keeps the type we're verifying has been removed.
 			string prefix = NamespacePrefix;