[ASDAlexander77]

Summary

A @cppvtable method can now be declared to return a struct by value, such as NVRHI's RefCountPtr<T> or nvrhi::Object. You declare the return type as a tuple with the struct's layout:

type RefCountPtr = [pointer: Opaque | null];       // nvrhi::RefCountPtr<T>
createBuffer(desc: Ref<BufferDesc>): RefCountPtr;  // const handle = device.createBuffer(Ref(desc));

MSVC returns any struct or class from a C++ instance method through a hidden pointer. The pointer is passed after this, and the method returns it as well (clang's MicrosoftCXXABI::classifyReturnType). Until now, tslang code had to declare that pointer as a parameter itself: createBuffer(ret: Ref<Opaque | null>, desc: Ref<BufferDesc>): Opaque.

How it works

• The method's slot type: mlirGenClassCppVTableHiddenReturn changes the slot type to (this, Ref<T>, args...) -> Ref<T>. The method's info still records the declared type, so DeclarationPrinter prints that and an importing module lowers it again.
• The call: a call creates a local of T and passes it after this. The call's value is that local, read back. The arguments' contextual types are shifted by one.
• Non-MSVC targets: the Itanium ABI passes the pointer before this, and only for some structs. On a target without TargetInfo::hiddenReturnPointerAfterThis (any non-MSVC target), such a method is a compile error.
• Method stored in a variable: if the method is stored in a variable and called later, the hidden pointer is not added for you; it is the first argument. Call the method directly instead. The docs say so.

Tests

• 00cppvtable_hidden_return.ts (compiled and JIT): returns an 8-byte and a 24-byte struct, with a plain scalar method in the same vtable. It also calls a base class's struct-returning method through a derived @cppvtable class.

• export_cppvtable_hidden_return.ts / import_cppvtable_hidden_return.ts (compiled and JIT): a method declared in the exporting module returns a struct, called from both modules.

• These tests run on Windows only (if (WIN32)), because on any other target such a method is an error.

• cppvtable/hidden_return_target.ts: checks the compile error on x86_64-unknown-linux-gnu.

• Full suite: 3999/3999 pass (ctest -C Release, windows-msbuild-2026-release).

• Real NVRHI: in a temporary copy of native_ts_graphics' core/nvrhi.ts, I switched these to the new form:

  • IDevice::createBuffer and IDevice::createCommandList, returning RefCountPtr;
  • IResource::getNativeObject, returning nvrhi::Object.

  examples/nvrhi_direct.ts passed on D3D12 and on Vulkan, with the debug layers on (-debug).

After this is in a release

native_ts_graphics' core/nvrhi.ts can drop the explicit ret parameters: createBuffer, createTexture, createCommandList, createComputePipeline, getNativeObject and getNativeQueue can return RefCountPtr or NativeObject tuples.

🤖 Generated with Claude Code