[mono] AOT-compile marshalling wrappers for layout classes with class-typed fields

[pavelsavara]

Summary

The Mono AOT compiler emits per-type StructureToPtr/PtrToStructure marshalling wrappers for [StructLayout] value types and sequential-layout classes, but only when can_marshal_struct() considers the type marshalable. That helper inspects each instance field and rejects the type if it encounters a field type it doesn't explicitly allow.

can_marshal_struct() had no case for MONO_TYPE_CLASS, so any layout class whose fields are themselves marshalable layout classes fell through to the default: branch and was treated as non-marshalable. A representative example is:

[StructLayout(LayoutKind.Sequential)]
class POINT { public int x, y; }

[StructLayout(LayoutKind.Sequential)]
class MINMAXINFO { public POINT ptMinTrackSize, ptMaxTrackSize; }

Because MINMAXINFO was rejected, its StructureToPtr/PtrToStructure wrappers were never emitted into the AOT image. The runtime marshals such a type just fine (it marshals the nested layout class as an embedded struct), so the call works under JIT, but under full-AOT the wrapper is generated on demand:

System.ExecutionEngineException: Attempting to JIT compile method
'(wrapper other) void MINMAXINFO:StructureToPtr (object,intptr,bool)'
while running in aot-only mode.

Fix

Handle MONO_TYPE_CLASS fields the same way as MONO_TYPE_VALUETYPE ΓÇö recurse into can_marshal_struct(). The existing mono_class_is_auto_layout() check at the top of the helper keeps the analysis conservative: non-layout class fields (e.g. object) still cause the type to be considered non-marshalable, while sequential/explicit-layout class fields recurse and are accepted when they are themselves marshalable.

With the fix, the MINMAXINFO/POINT StructureToPtr/PtrToStructure wrappers are present in the AOT image and the call succeeds under full-AOT.

Testing

Re-enables the JIT/Regression/JitBlue/WPF_3226 test on Mono (the [ActiveIssue] annotation is removed so CI exercises the fix). Validated locally with an x64 Mono LLVM full-AOT build: the wrappers now appear in the AOT image and the test passes (it previously crashed with the ExecutionEngineException above).

Note

This change was authored with the assistance of GitHub Copilot.

---

Part of the MonoAOT LLVM 23 full-AOT regression set tracked by #129508. Built and tested together with the Emscripten 5.0.6 / LLVM 23 bump on #129396, where the re-enabled WPF_3226 test passes on the runtime-llvm AllSubsets_Mono_LLVMFULLAOT_RuntimeTests leg.

Contributes to #129508.

[Copilot]

Pull request overview

This PR updates Mono’s AOT wrapper inclusion logic so sequential/explicit-layout classes with class-typed fields can be considered marshalable (enabling StructureToPtr/PtrToStructure wrappers to be emitted ahead-of-time), and re-enables a regression test on Mono.

Changes:

• Extend can_marshal_struct() to handle MONO_TYPE_CLASS fields by recursing into the nested class.
• Re-enable WPF_3226 regression coverage on Mono by removing the [ActiveIssue] skip.

Reviewed changes

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

File	Description
src/mono/mono/mini/aot-compiler.c	Adds MONO_TYPE_CLASS handling in can_marshal_struct() to allow nested layout classes to qualify for AOT marshalling wrappers.
src/tests/JIT/Regression/JitBlue/WPF_3226/CSharpRepro/WPF_3226.cs	Removes Mono-specific [ActiveIssue] skip so CI exercises the scenario again.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

[pavelsavara]

/ba-g unrelated failures