[dotnet] Implement support for our different link modes. (xamarin#9460)

* [mmp] Rename LinkMode.All to LinkMode.Full.

So that we can continue to use Enum.Parse<LinkMode> to parse 'Full' as the link mode.

* [dotnet] Implement support for our different link modes.

Tell the managed linker what to do with each input assembly depending the selected
link mode (link all, link sdk, don't link).

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -116,7 +116,10 @@
 		<_AdditionalTaskAssemblyDirectory>$(_XamarinSdkRootDirectory)tools/dotnet-linker/</_AdditionalTaskAssemblyDirectory>
 		<_AdditionalTaskAssembly>$(_AdditionalTaskAssemblyDirectory)dotnet-linker.dll</_AdditionalTaskAssembly>
 	</PropertyGroup>
-	<Target Name="_ComputeLinkerArguments" DependsOnTargets="_ComputeLinkMode">
+	<Target Name="_ComputeLinkerArguments" DependsOnTargets="_ComputeLinkMode;ComputeResolvedFilesToPublishList">
+		<!-- Validate the linker mode -->
+		<Error Text="Invalid link mode: '$(_LinkMode)'. Valid link modes are: 'None', 'SdkOnly' and 'Full'" Condition="'$(_LinkMode)' != 'None' And '$(_LinkMode)' != 'SdkOnly' And '$(_LinkMode)' != 'Full'" />
+
 		<PropertyGroup>
 			<!-- Pass the custom options to our custom steps -->
 			<_CustomLinkerOptionsFile>$([System.IO.Path]::GetFullPath('$(IntermediateOutputPath)custom-linker-options.txt'))</_CustomLinkerOptionsFile>
@@ -146,6 +149,11 @@
 			<!-- System.Runtime.dll isn't always copied to the .app -->
 			<_ExtraTrimmerArgs>$(_ExtraTrimmerArgs) -p copy "System.Runtime"</_ExtraTrimmerArgs>
 
+			<!-- TrimMode specifies what the linker will do with framework assemblies -->
+			<TrimMode Condition="'$(_LinkMode)' == 'None'">copy</TrimMode> <!-- Don't use 'copyused', because that might still end up saving some assemblies, and if that's the platform assembly, it may break the partial static registrar -->
+			<TrimMode Condition="'$(_LinkMode)' == 'SdkOnly' Or '$(_LinkMode)' == 'Full'">link</TrimMode>
+			<!-- For Full link mode we also need to set TrimMode for all non-framework assemblies. This is done further below -->
+
 			<!-- Verbose output, so that we get something to stdout when something goes wrong -->
 			<_ExtraTrimmerArgs>$(_ExtraTrimmerArgs) --verbose</_ExtraTrimmerArgs>
 
@@ -161,7 +169,19 @@
 			-->
 			<_ExtraTrimmerArgs>$(_ExtraTrimmerArgs) -b</_ExtraTrimmerArgs>
 		</PropertyGroup>
+
 		<ItemGroup>
+			<!-- Mark all assemblies to be linked if we're linking all assemblies -->
+			<ResolvedFileToPublish
+				Update="@(ResolvedFileToPublish)"
+				Condition="'$(_LinkMode)' == 'Full' And '%(ResolvedFileToPublish.Extension)' == '.dll' And '%(ResolvedFileToPublish.AssetType)' != 'native'"
+			>
+				<TrimMode>link</TrimMode>
+			</ResolvedFileToPublish>
+
+			<!-- Mark our entry assembly as a root assembly. -->
+			<TrimmerRootAssembly Include="$(AssemblyName)" />
+
 			<!-- add a custom step which inserts any other steps we need -->
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)">
 				<BeforeStep>LoadReferencesStep</BeforeStep>

tools/common/Application.cs

@@ -74,7 +74,7 @@ public partial class Application
 		public ApplePlatform Platform { get { return Driver.TargetFramework.Platform; } }
 
 		// Linker config
-		public LinkMode LinkMode = LinkMode.All;
+		public LinkMode LinkMode = LinkMode.Full;
 		public List<string> LinkSkipped = new List<string> ();
 		public List<string> Definitions = new List<string> ();
 		public I18nAssemblies I18n;

tools/common/LinkMode.cs

@@ -8,7 +8,7 @@ namespace Xamarin.Bundler {
 	public enum LinkMode {
 		None,
 		SDKOnly,
-		All,
+		Full,
 		Platform,
 	}
 }

tools/mmp/driver.cs

@@ -599,7 +599,7 @@ static void Pack (IList<string> unprocessed)
 			if (generate_plist)
 				GeneratePList ();
 
-			if (App.LinkMode != LinkMode.All && App.RuntimeOptions != null)
+			if (App.LinkMode != LinkMode.Full && App.RuntimeOptions != null)
 				App.RuntimeOptions.Write (resources_dir);
 
 			if (App.AOTOptions != null && App.AOTOptions.IsAOT) {