PostTrimmingPipeline.cs

#nullable enable

using System.Collections.Generic;
using System.IO;
using Java.Interop.Tools.Cecil;
using Microsoft.Android.Build.Tasks;
using Microsoft.Build.Framework;
using Mono.Cecil;
using MonoDroid.Tuner;

namespace Xamarin.Android.Tasks;

/// <summary>
/// An MSBuild task that runs post-trimming assembly modifications in a single pass.
///
/// This opens each assembly once (via DirectoryAssemblyResolver with ReadWrite) and
/// runs all registered steps on it, then writes modified assemblies in-place. Currently
/// runs StripEmbeddedLibrariesStep and (optionally) AddKeepAlivesStep.
///
/// Runs in the inner build after ILLink but before ReadyToRun/crossgen2 compilation,
/// so that R2R images are generated from the already-modified assemblies.
/// </summary>
public class PostTrimmingPipeline : AndroidTask
{
	public override string TaskPrefix => "PTP";

	[Required]
	public ITaskItem [] Assemblies { get; set; } = [];

	public bool AddKeepAlives { get; set; }

	public bool Deterministic { get; set; }

	public override bool RunTask ()
	{
		using var resolver = new DirectoryAssemblyResolver (
			this.CreateTaskLogger (), loadDebugSymbols: true,
			loadReaderParameters: new ReaderParameters { ReadWrite = true });
		var cache = new TypeDefinitionCache ();

		foreach (var assembly in Assemblies) {
			var dir = Path.GetFullPath (Path.GetDirectoryName (assembly.ItemSpec) ?? "");
			if (!resolver.SearchDirectories.Contains (dir)) {
				resolver.SearchDirectories.Add (dir);
			}
		}

		var steps = new List<IAssemblyModifierPipelineStep> ();
		steps.Add (new StripEmbeddedLibrariesStep (Log));
		if (AddKeepAlives) {
			// Memoize the corlib resolution so the attempt (and any error logging) happens at most once,
			// regardless of how many assemblies/methods need KeepAlive injection.
			AssemblyDefinition? corlibAssembly = null;
			bool corlibResolutionAttempted = false;
			steps.Add (new PostTrimmingAddKeepAlivesStep (cache,
				() => {
					if (!corlibResolutionAttempted) {
						corlibResolutionAttempted = true;
						try {
							corlibAssembly = resolver.Resolve (AssemblyNameReference.Parse ("System.Private.CoreLib"));
						} catch (AssemblyResolutionException ex) {
							Log.LogErrorFromException (ex, showStackTrace: false);
						}
					}
					return corlibAssembly;
				},
				(msg) => Log.LogDebugMessage (msg)));
		}

		foreach (var item in Assemblies) {
			var assembly = resolver.GetAssembly (item.ItemSpec);
			var context = new StepContext (item, item);
			foreach (var step in steps) {
				step.ProcessAssembly (assembly, context);
			}
			if (context.IsAssemblyModified) {
				Log.LogDebugMessage ($"  Writing modified assembly: {item.ItemSpec}");
				assembly.Write (new WriterParameters {
					WriteSymbols = assembly.MainModule.HasSymbols,
					DeterministicMvid = Deterministic,
				});
			}
		}

		return !Log.HasLoggedErrors;
	}
}