Feature Request: Allow partial custom activation handlers #1345
Description
Version
C++/WinRT v2.0.220110.5
Summary
The conversation #477 (comment) suggests that it's desirable to have a way for an activation handler to return back to the default procedure in case it's not interested in a certain class. That's useful when tests deal with a couple of WinRT types, but only part of them are to be mocked.
The inclusion of the global winrt_activation_handler in #477 requires the custom activation handler to deal with all possible activation scenarios. In certain kinds of tests that might be an overkill.
A small change as suggested below would allow handlers by convention to return a magic value meaning they cannot handle that activation and the original procedure should take over.
if (winrt_activation_handler)
{
if (auto hr = winrt_activation_handler(*(void**)(&name), guid_of<Interface>(), result);
hr != impl::error_not_implemented) {
return hr;
}
}Augmenting test\custom_activation.cpp to try instantiating some other class the custom_factory is not interested in would result in a uncorrectable failure (even if we'd remove the REQUIRE clauses from the handler and the custom_factory implementation code).
Reproducible example
// in the end of `test\custom_activation.cpp`
// An activation handler that doesn't handle WwwFormUrlDecoder activation.
bool invoked_unimplemented = false;
int32_t __stdcall another_handler(void* classId, winrt::guid const& iid, void** factory) noexcept
{
if (iid == guid_of<IWwwFormUrlDecoderRuntimeClassFactory>()) {
invoked_unimplemented = true;
return winrt::impl::error_not_implemented;
}
*factory = detach_abi(make<custom_factory>());
return 0;
}
TEST_CASE("partial_custom_activation")
{
clear_factory_cache();
// Set up global handler
REQUIRE(!winrt_activation_handler);
winrt_activation_handler = another_handler;
REQUIRE(!invoked_unimplemented);
// Activates something the handler cannot deal with. It shouldn't crash and the decoder should behave normally.
WwwFormUrlDecoder decoder{ L"uname=c&passwd=d" };
REQUIRE(invoked_unimplemented);
REQUIRE(decoder.GetFirstValueByName(L"uname") == L"c");
REQUIRE(decoder.GetFirstValueByName(L"passwd") == L"d");
// Remove global handler
winrt_activation_handler = nullptr;
clear_factory_cache();
}Expected behavior
No failure, no crash, the custom handler would defer activating the unhandled classes to the default procedure.
Actual behavior
The custom handler must handle all possible activations or crash (SIGSEGV)
Additional comments
No response