Hit the max nesting depth, but to reply about why, because winrt::import! is reading (arbitrary?) filesystem paths and there isn't an equivalent for build.rs emitting 'rerun-if-changed'.

So, neither cargo nor the compiler really know of the paths, and cannot accordingly rebuild the sources when they change.

Perhaps they can only change when a corresponding version cargo does know about changes, anyhow, bypassing the build/module system with a proc macro is probably not something to be done lightly.