[Build] Add Inputs/Outputs to _GenerateCompressedAssembliesNativeSourceFiles

[jonathanpeppers]

Description

_GenerateCompressedAssembliesNativeSourceFiles took 147ms on an
incremental build because it had no Inputs/Outputs — it ran every
time regardless of whether any assemblies changed.

This PR adds:

• Inputs: @(_ResolvedUserAssemblies);@(_ResolvedFrameworkAssemblies);$(_AndroidBuildPropertiesCache)
• Outputs: @(_CompressedAssembliesAssemblySource) (the .ll files,
  already populated by _PrepareNativeAssemblySourceItems)

This should prevent the target from running on a build with no changes.

Also updates BasicApplicationRepetitiveBuild to assert the target is
skipped on a no-change rebuild.

[Copilot]

Pull request overview

Adds MSBuild incremental build semantics to _GenerateCompressedAssembliesNativeSourceFiles so it can be skipped on no-change rebuilds, and updates an incremental build test to assert the skip behavior.

Changes:

• Add Inputs/Outputs to _GenerateCompressedAssembliesNativeSourceFiles in Xamarin.Android.Common.targets.
• Update BasicApplicationRepetitiveBuild to assert _GenerateCompressedAssembliesNativeSourceFiles is skipped on a no-change rebuild.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets	Adds MSBuild incremental inputs/outputs to avoid re-running compressed-assemblies native source generation on unchanged builds.
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/IncrementalBuildTest.cs	Adds an assertion that the target is skipped on the second build.

[Copilot]

AssertTargetIsSkipped ("_GenerateCompressedAssembliesNativeSourceFiles") is unconditional, but _GenerateCompressedAssembliesNativeSourceFiles is conditioned out when runtime == AndroidRuntime.NativeAOT. If the NativeAOT build path doesn’t invoke the target (and therefore doesn’t emit a “skipped” message), this assertion will fail. Consider guarding the assertion to non-NativeAOT runtimes, or pass defaultIfNotUsed: true for the NativeAOT case.

Suggested change

	b.Output.AssertTargetIsSkipped ("_GenerateCompressedAssembliesNativeSourceFiles");
	if (runtime != AndroidRuntime.NativeAOT) {
	b.Output.AssertTargetIsSkipped ("_GenerateCompressedAssembliesNativeSourceFiles");
	}

[jonathanpeppers]

Ok, this breaks things, due to:

Root cause: _GenerateCompressedAssembliesNativeSourceFiles calls
RegisterTaskObjectAssemblyLocal to pass compression metadata to
CollectAssemblyFilesForArchive. When Inputs/Outputs skips the target
on incremental builds, that registration never happens.

CollectAssemblyFilesForArchive then throws:
  "Assembly compression info not found for key '{key}'"

This only affects Release builds with compression enabled (Debug
builds skip registration entirely via the early-exit on line 42).

Fix: The task needs to write the compression info to a file (like a
.cache file) instead of using RegisterTaskObjectAssemblyLocal. Then
CollectAssemblyFilesForArchive reads from the file. This way the
target can be skipped and the data persists across builds.

I would say we should finish trimmable type map, which removes RegisterTaskObject() usage.