Expose is_sub_type reflection api (#121)

* support for is_sub_type api

* Tweak subtype test

src/sgl/device/python/reflection.cpp

@@ -207,6 +207,7 @@ SGL_PY_EXPORT(device_reflection)
             D_NA(ProgramLayout, find_function_by_name_in_type)
         )
         .def("get_type_layout", &ProgramLayout::get_type_layout, "type"_a, D_NA(ProgramLayout, get_type_layout))
+        .def("is_sub_type", &ProgramLayout::is_sub_type, "sub_type"_a, "super_type"_a, D_NA(ProgramLayout, is_sub_type))
         .def_prop_ro("hashed_strings", &ProgramLayout::hashed_strings, D(ProgramLayout, hashed_strings))
         .def("__repr__", &ProgramLayout::to_string);
 

src/sgl/device/reflection.h

@@ -1014,13 +1014,20 @@ class SGL_API ProgramLayout : public BaseReflectionObjectImpl<slang::ProgramLayo
 
     /// Find a given function in a type by name. Handles generic specilization if generic
     /// variable values are provided.
-    ref<const FunctionReflection> find_function_by_name_in_type(TypeReflection* type, const char* name)
+    ref<const FunctionReflection> find_function_by_name_in_type(const TypeReflection* type, const char* name)
     {
         return detail::from_slang(m_owner, m_target->findFunctionByNameInType(type->slang_target(), name));
     }
 
+    /// Test whether a type is a sub type of another type. Handles both
+    /// struct inheritance and interface implementation.
+    bool is_sub_type(const TypeReflection* sub_type, const TypeReflection* super_type)
+    {
+        return m_target->isSubType(sub_type->slang_target(), super_type->slang_target());
+    }
+
     /// Get corresponding type layout from a given type.
-    ref<const TypeLayoutReflection> get_type_layout(TypeReflection* type)
+    ref<const TypeLayoutReflection> get_type_layout(const TypeReflection* type)
     {
         // TODO: Once device is available via session reference, pass metal layout rules for metal target
         return detail::from_slang(m_owner, m_target->getTypeLayout(type->slang_target(), slang::LayoutRules::Default));

src/sgl/device/tests/test_reflection.py

@@ -669,5 +669,47 @@ def test_get_type_layout(test_id: str, device_type: sgl.DeviceType):
     assert tl.size == 4
 
 
+@pytest.mark.parametrize("device_type", helpers.DEFAULT_DEVICE_TYPES)
+def test_is_sub_type(test_id: str, device_type: sgl.DeviceType):
+    device = helpers.get_device(type=device_type)
+
+    # Create a session, and within it a module.
+    session = helpers.create_session(device, {})
+    module = session.load_module_from_source(
+        module_name=f"module_from_source_{test_id}",
+        source="""
+        interface IHello {
+        }
+        struct Hello : IHello {
+            int a;
+        }
+
+        interface IHello2 {
+        }
+        extension Hello : IHello2 {
+        }
+    """,
+    )
+
+    t = module.layout.find_type_by_name("Hello")
+    assert t is not None
+    assert t.name == "Hello"
+
+    # t should be a sub type of itself.
+    assert module.layout.is_sub_type(t, t)
+
+    # t should be a sub type of its interface.
+    i = module.layout.find_type_by_name("IHello")
+    assert i is not None
+    assert i.name == "IHello"
+    assert module.layout.is_sub_type(t, i)
+
+    # t should be a sub type of its extension.
+    i2 = module.layout.find_type_by_name("IHello2")
+    assert i2 is not None
+    assert i2.name == "IHello2"
+    assert module.layout.is_sub_type(t, i)
+
+
 if __name__ == "__main__":
     pytest.main([__file__, "-v"])