[msbuild/tools] Move post-trimming custom trimmer steps to a post-ILLink MSBuild task. by rolfbjarne · Pull Request #25742 · dotnet/macios

rolfbjarne · 2026-06-18T16:43:00Z

WIP WIP WIP.

Contributes towards #17693.

…teps.

…embly in the AssemblyPreparerInfo.

…thod.

…tep.

…step.

Copilot

Pull request overview

This PR is a WIP step toward replacing custom ILLink linker steps by moving the “post-trimming” work into an MSBuild task (assembly preparer mode), enabling a trimmer-agnostic pipeline (ILLink and future NativeAOT scenarios).

Changes:

Introduces an MSBuild-driven post-processing phase for prepared assemblies (PostProcessAssemblies + _PostprocessAssemblies target).
Refactors/extends assembly-preparer to load assemblies, run pre/post steps, and save results (new steps + expanded pipeline).
Adapts several linker steps to run both in the traditional linker pipeline and in assembly-preparer mode; adds a Windows remote test for assembly preparer.

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
tools/linker/RemoveUserResourcesSubStep.cs	Updates the step to work in both linker and assembly-preparer pipelines.
tools/linker/MonoTouch.Tuner/ListExportedSymbols.cs	Adds ASSEMBLY_PREPARER support for the step.
tools/dotnet-linker/Steps/RegistrarStep.cs	Adjusts registrar filtering behavior for assembly-preparer mode.
tools/dotnet-linker/Steps/GenerateReferencesStep.cs	Switches to `StringUtils.IsNullOrEmpty` for consistency.
tools/dotnet-linker/Steps/ExtractBindingLibrariesStep.cs	Uses `PathUtils.AbsoluteToRelative` instead of `Path.GetRelativePath`.
tools/dotnet-linker/LinkerConfiguration.cs	Extends configuration for assembly-preparer mode (AssemblyInfos, etc).
tools/common/Application.cs	Adds an explicit `IsPostProcessingAssemblies` flag for assembly-preparer mode.
tools/assembly-preparer/SaveAssembliesStep.cs	New step to write assemblies after processing (and strip crossgen markers).
tools/assembly-preparer/LoadAssembliesStep.cs	New step to load assemblies + determine trimming action.
tools/assembly-preparer/ComputeMethodOverridesStep.cs	New step to precompute method overrides into annotations.
tools/assembly-preparer/CollectFieldsStep.cs	New step to collect exported field symbols (compat for InlineDlfcn).
tools/assembly-preparer/AssemblyPreparer.cs	Splits pipeline into Prepare vs PostProcess and runs step lists accordingly.
tools/assembly-preparer/assembly-preparer.csproj	Wires additional steps and dependencies into the assembly-preparer tool.
tests/dotnet/UnitTests/WindowsTest.cs	Adds a remote Windows test validating assembly-preparer behavior/artifacts.
msbuild/Xamarin.Shared/Xamarin.Shared.targets	Adds `PostProcessAssemblies` and introduces `_PostprocessAssemblies` target.
msbuild/Xamarin.MacDev.Tasks/Tasks/PrepareAssemblies.cs	Adds a post-processing mode invocation path for `AssemblyPreparer`.
dotnet/targets/Xamarin.Shared.Sdk.targets	Avoids running existing custom trimmer steps when post-processing is enabled.

@@ -44,6 +54,7 @@ protected override void EndProcess ()
 			base.EndProcess ();
 		}


+	<Target
+		Name="_PostprocessAssemblies"
+		Condition="'$(PrepareAssemblies)' == 'true'"
+		Inputs="@(_PreparedAssemblies)"
+		Outputs="$(_PrepareAssembliesStampFile)"
+		BeforeTargets="_LoadLinkerOutput"
+		>
+		<PrepareAssemblies
+			InputAssemblies="@(_PreparedAssemblies)"
+			MakeReproPath="$(_PostprocessAssembliesMakeReproPath)"
+			OptionsFile="$(_CustomLinkerOptionsFile)"
+			OriginalAssemblies="$(_AssembliesToPrepare)"
+			Postprocessing="true"
+			TargetFrameworkMoniker="$(_ComputedTargetFrameworkMoniker)"
+		>
+			<Output TaskParameter="OutputAssemblies" ItemName="_PostProcessedAssemblies" />
+		</PrepareAssemblies>
+
+		<ItemGroup>
+			<ResolvedFileToPublish Remove="@(_PreparedAssemblies)" />
+			<ResolvedFileToPublish Include="@(_PostProcessedAssemblies)" />
+			<FileWrites Include="@(_PostProcessedAssemblies)" />
+		</ItemGroup>
+	</Target>


+			foreach (var assembly in configuration.AssemblyInfos) {
+				var assemblyDefinition = assembly.Assembly;
+				if (assemblyDefinition is null) {
+					exceptions.Add (ErrorHelper.CreateError (99, $"Assembly definition is null for {assembly.InputPath}"));
+					return;
+				}


+				try {
+					assemblyDefinition.Write (assembly.OutputPath, writerParameters);
+					ModuleAttributes m = assemblyDefinition.MainModule.Attributes;
+				} catch (Exception e) {


@@ -0,0 +1,89 @@
+// Copilot: add license


@@ -0,0 +1,124 @@
+// Copilot: add license


@@ -0,0 +1,57 @@
+// Copilot: add license


@@ -0,0 +1,14 @@
+// Copilot: add license


+			using var memoryStream = new MemoryStream ((int) infoPlistEntry!.Length);
+			using var plistStream = infoPlistEntry.Open ();
+			plistStream.CopyTo (memoryStream);
+
+			var infoPlist = (PDictionary) PDictionary.FromStream (memoryStream)!;


+		public ITaskItem [] OriginalAssemblies { get; set; } = [];
+
+		public bool PostProcessing { get; set; }


vs-mobiletools-engineering-service2 · 2026-06-18T17:07:42Z

✅ [PR Build #8a3a11e] Build passed (Detect API changes) ✅

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vs-mobiletools-engineering-service2 · 2026-06-18T17:15:59Z

✅ [PR Build #8a3a11e] Build passed (Build packages) ✅

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vs-mobiletools-engineering-service2 · 2026-06-18T17:20:16Z

✅ API diff for current PR / commit

NET (empty diffs)

iOS: vsdrops gist ( No breaking changes )
tvOS: vsdrops gist ( No breaking changes )
MacCatalyst: vsdrops gist ( No breaking changes )
macOS: vsdrops gist ( No breaking changes )

✅ API diff vs stable

NET (empty diffs)

iOS: vsdrops gist ( No breaking changes )
tvOS: vsdrops gist ( No breaking changes )
MacCatalyst: vsdrops gist ( No breaking changes )
macOS: vsdrops gist ( No breaking changes )

ℹ️ Generator diff

Generator Diff: vsdrops (html) vsdrops (raw diff) gist (raw diff) - Please review changes)

Pipeline on Agent
Hash: 8a3a11e9479a1a25a81fe00bce448498b75c8764 [PR build]

vs-mobiletools-engineering-service2 · 2026-06-18T17:25:40Z

✅ [PR Build #8a3a11e] Build passed (Build macOS tests) ✅

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Hash: 8a3a11e9479a1a25a81fe00bce448498b75c8764 [PR build]

vs-mobiletools-engineering-service2 · 2026-06-18T18:58:22Z

🔥 [CI Build #8a3a11e] Test results 🔥

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❌ Tests failed on VSTS: test results

0 tests crashed, 61 tests failed, 159 tests passed.