But building something more complex in Rust (than just grabbing a bunch of libraries from Cargo) becomes as tedious as what you typically expect in C++ land. I've read anecdotes of Rust devs struggling with build.rs (the official build scripting in Rust) similarly to how people bang their heads at CMake.

This is why other C++ build systems like Bazel and Meson added Rust support, since Cargo/build.rs itself isn't sufficient enough for all use cases (especially when using it alongside with other systems languages.) And it's not too wild for something to think of adding Rust support for CMake as well...

You have chatGPT, come on