Bug: Enable configuration for activation fallback

[jonwis]

Version

2.0.220131.2

Summary

winrt::impl::get_runtime_activation_factory_impl does the following:

1. If the DLL has set a handler callback, call it and return.
2. Try to use Windows' RoGetActivationFactory, if present, and the type's factory is available, return it.
3. Do type-name based probing (Contoso.Foo.Bar.dll, Contoso.Foo.dll, Contoso.dll) for DLLs and use those

Certain projects really only want items 1 & 2 above. Provide a control point for 3. Path based probing can induce surprise behavior when DLLs have overlapping names.

Reproducible example

No response

Expected behavior

No response

Actual behavior

No response

Additional comments

After talking with @oldnewthing , I suggest:

• Move the name-based probing to a new method, like winrt::find_dll_factory
• Change get_runtime_activation_factory_impl to use a callback pointer, like winrt_fallback_handler
• Document how to say winrt_activation_handler = winrt::fallback_handler if your module needs fallback

This makes the default behavior "you have to get your stuff registered in a side-by-side or package manifest, or you have to be using a built-in or Windows type" with support for projects who prefer reg-free operation.

[dmachaj]

Number 3 on that list is sometimes unsafe. It may be nice to bring forward the changes from #1414 so that projects have control over whether that is active.

[github-actions]

This issue is stale because it has been open 10 days with no activity. Remove stale label or comment or this will be closed in 5 days.