Add AssociatedSourceType for conditional unmanaged exports

[Copilot]

UnmanagedCallersOnlyAttribute exports with EntryPoint were always rooted and emitted. This adds an associated source type so NativeAOT can keep/export generated native entrypoints only when the source type survives trimming.

• Public API
  • Adds UnmanagedCallersOnlyAttribute.AssociatedSourceType to implementation and ref assemblies.
  • Leaves the lightweight Runtime.Base attribute copy unchanged.

[UnmanagedCallersOnly(
    EntryPoint = "MyObjectProxy_MyMethod",
    AssociatedSourceType = typeof(MyObject))]
static void MyMethod(IntPtr handle) { }

• NativeAOT rooting

  • Moves unmanaged entrypoint rooting into a per-assembly UnmanagedEntryPointsNode.
  • Roots normal exports unconditionally.
  • Roots associated exports conditionally on runtime-constructable AssociatedSourceType.
  • Skips associated exports when the associated source type cannot be resolved.
  • Handles associated source types that can be dynamically constructed at runtime, including generic source types and array types without array templates.

• Shared trim-target dependency handling

  • Extracts runtime-constructable trim-target dependency logic into RuntimeConstructableTypeDependencies.
  • Reuses the helper from both unmanaged entrypoint rooting and external type map handling.

• Export generation

  • Filters generated export files to compiled method bodies so trimmed associated exports are not passed to the native linker.

• Coverage

  • Adds TrimmingBehaviors coverage for unconditional, kept associated, trimmed associated, unused array associated-source, dynamically loadable generic associated-source, dynamically loadable array associated-source, and array associated-source constructed through a runtime generic array template.

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[MichalStrehovsky]

@copilot

[AaronRobinsonMSFT]

Why does this definition of UnmanagedCallersOnlyAttribute exist? Shouldn't this just use the one in SPCL via a source include or something?

[MichalStrehovsky]

We could, but this rarely changes and Runtime.Base is supposed to be low overhead and ceremony (i.e. people shouldn't have to deal with Runtime.Base build breaks if they modify a file in CoreLib). E.g. we also define the CallConvs types in this file, the ones that we needed.

This addition is unnecessary. @copilot revert changes in this file

[Copilot]

Reverted the unnecessary Runtime.Base attribute copy change in 3494d17.

[MichalStrehovsky]

@copilot

[MichalStrehovsky]

@copilot

[MichalStrehovsky]

Suggested change

	if (compilationResults.IsMethodBodyCompiled(method))
	// Some of the exported methods could be conditioned with UnmanagedCallersOnly.AssociatedSourceType
	// so need to filter down to compiled methods.
	if (compilationResults.IsMethodBodyCompiled(method))

[MichalStrehovsky]

Add one more test that uses AssociatedSourceType = typeof(UnusedSource[]) (array of the type). Since the element type is never referenced, that one should not be generated either.

Then add one more test that uses AssociatedSourceType = typeof(UsedAsElementOnly[]) and make sure we use that with a public static object CreateArray<T>() => new T[0]; that is reached through MakeGenericMethod. The associated export should be generated because we constructed the array through a template at runtime.

[MichalStrehovsky]

You can eliminate this warning by constraining the T in methods used with MakeGeneric to be a class. Example: public static object CreateDynamicSource<T>() where T : class => new DynamicSource<T>();. No warnings are generated for these because we can construct the method at runtime.