[dotnet] Only pass a single custom step to the linker. (#9173)

* [dotnet] Only pass a single custom step to the linker.

The linker will load the assemblies with the custom steps once per custom step
argument, which means that each step is effectively in a different assembly,
making it impossible to share state between steps.

This behavior is filed as a linker bug: https://github.com/mono/linker/issues/1314

Until this is fixed, we can just have a single step that injects all the other
steps programmatically.

* [tests] Adjust .NET tests according to new behavior.

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -149,19 +149,11 @@
 			<_ExtraTrimmerArgs>$(_ExtraTrimmerArgs) --verbose</_ExtraTrimmerArgs>
 		</PropertyGroup>
 		<ItemGroup>
-			<!-- add our custom steps -->
+			<!-- add a custom step which inserts any other steps we need -->
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)">
 				<BeforeStep>LoadReferencesStep</BeforeStep>
 				<Type>Xamarin.SetupStep</Type>
 			</_TrimmerCustomSteps>
-			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)">
-				<!-- At the end of the pipeline -->
-				<Type>Xamarin.GenerateMainStep</Type>
-			</_TrimmerCustomSteps>
-			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)">
-				<!-- At the end of the pipeline -->
-				<Type>Xamarin.GatherFrameworksStep</Type>
-			</_TrimmerCustomSteps>
 		</ItemGroup>
 
 		<!-- Create the file with our custom linker options -->

tests/dotnet/UnitTests/ProjectTest.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
 
 using NUnit.Framework;
@@ -8,6 +9,8 @@ using Xamarin.Utils;
 namespace Xamarin.Tests {
 	[TestFixture]
 	public class DotNetProjectTest {
+		Dictionary<string, string> verbosity = new Dictionary<string, string> { { "_BundlerVerbosity", "1" } };
+
 		string GetProjectPath (string project, string subdir = null)
 		{
 			var project_dir = Path.Combine (Configuration.SourceRoot, "tests", "dotnet", project);
@@ -41,7 +44,7 @@ namespace Xamarin.Tests {
 			var platform = ApplePlatform.iOS;
 			var project_path = GetProjectPath ("MySingleView");
 			Clean (project_path);
-			var result = DotNet.AssertBuild (project_path);
+			var result = DotNet.AssertBuild (project_path, verbosity);
 			AssertThatLinkerExecuted (result);
 			AssertAppContents (platform, Path.Combine (Path.GetDirectoryName (project_path), "bin", "Debug", "net5.0", "ios-x64", "MySingleView.app"));
 		}
@@ -52,7 +55,7 @@ namespace Xamarin.Tests {
 			var platform = ApplePlatform.MacOSX;
 			var project_path = GetProjectPath ("MyCocoaApp");
 			Clean (project_path);
-			var result = DotNet.AssertBuild (project_path);
+			var result = DotNet.AssertBuild (project_path, verbosity);
 			AssertThatLinkerExecuted (result);
 			AssertAppContents (platform, Path.Combine (Path.GetDirectoryName (project_path), "bin", "Debug", "net5.0", "osx-x64", "MyCocoaApp.app"));
 		}
@@ -63,7 +66,7 @@ namespace Xamarin.Tests {
 			var platform = ApplePlatform.TVOS;
 			var project_path = GetProjectPath ("MyTVApp");
 			Clean (project_path);
-			var result = DotNet.AssertBuild (project_path);
+			var result = DotNet.AssertBuild (project_path, verbosity);
 			AssertThatLinkerExecuted (result);
 			AssertAppContents (platform, Path.Combine (Path.GetDirectoryName (project_path), "bin", "Debug", "net5.0", "tvos-x64", "MyTVApp.app"));
 		}
@@ -73,7 +76,7 @@ namespace Xamarin.Tests {
 		{
 			var project_path = GetProjectPath ("MyWatchApp");
 			Clean (project_path);
-			var result = DotNet.AssertBuildFailure (project_path);
+			var result = DotNet.AssertBuildFailure (project_path, verbosity);
 			Assert.That (result.StandardOutput.ToString (), Does.Contain ("The specified RuntimeIdentifier 'watchos-x86' is not recognized."), "Missing runtime pack for watchOS");
 		}
 
@@ -85,7 +88,7 @@ namespace Xamarin.Tests {
 		{
 			var project_path = GetProjectPath ("MyClassLibrary", platform);
 			Clean (project_path);
-			var result = DotNet.AssertBuild (project_path);
+			var result = DotNet.AssertBuild (project_path, verbosity);
 			Assert.That (result.StandardOutput.ToString (), Does.Not.Contain ("Task \"ILLink\""), "Linker executed unexpectedly.");
 		}
 
@@ -93,7 +96,7 @@ namespace Xamarin.Tests {
 		{
 			var output = result.StandardOutput.ToString ();
 			Assert.That (output, Does.Contain ("Building target \"_RunILLink\" completely."), "Linker did not executed as expected.");
-			Assert.That (output, Does.Contain ("Hello SetupStep"), "Custom steps did not run as expected.");
+			Assert.That (output, Does.Contain ("Pipeline Steps:"), "Custom steps did not run as expected.");
 		}
 
 		void AssertAppContents (ApplePlatform platform, string app_directory)

tools/dotnet-linker/SetupStep.cs

@@ -1,6 +1,9 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
+using System.Reflection;
 
+using Mono.Linker;
 using Mono.Linker.Steps;
 
 using Xamarin.Bundler;
@@ -10,12 +13,35 @@ namespace Xamarin {
 
 	public class SetupStep : ConfigurationAwareStep {
 
+		List<IStep> _steps;
+		public List<IStep> Steps {
+			get {
+				if (_steps == null) {
+					var pipeline = typeof (LinkContext).GetProperty ("Pipeline").GetGetMethod ().Invoke (Context, null);
+					_steps = (List<IStep>) pipeline.GetType ().GetField ("_steps", BindingFlags.Instance | BindingFlags.NonPublic).GetValue (pipeline);
+				}
+				return _steps;
+			}
+		}
+
 		protected override void Process ()
 		{
-			// This will be replaced with something more useful later.
-			Console.WriteLine ("Hello SetupStep");
+			// Don't use --custom-step to load each step, because this assembly
+			// is loaded into the current process once per --custom-step,
+			// which makes it very difficult to share state between steps.
+			Steps.Add (new GenerateMainStep ());
+			Steps.Add (new GatherFrameworksStep ());
+
 			Configuration.Write ();
 
+			if (Configuration.Verbosity > 0) {
+				Console.WriteLine ();
+				Console.WriteLine ("Pipeline Steps:");
+				foreach (var step in Steps) {
+					Console.WriteLine ($"    {step}");
+				}
+			}
+
 			ErrorHelper.Platform = Configuration.Platform;
 			Directory.CreateDirectory (Configuration.ItemsDirectory);
 			Directory.CreateDirectory (Configuration.CacheDirectory);