Yes, I started out by using genrule before going down the custom rule path. I was able to properly trigger bazel to generate the interface bindings but then lost the thread when trying to properly configure the output files to act as proper dependencies to other code (ie. generate C++ headers and libraries that could then be properly listed as dependencies by client code.)

I think part of the issue was that the generated code from the 3rd party tool did not align with the Bazel expectations about code layout (ie. paths relative to WORKSPACE). Likely solvable but not in the amount of time I had available to dedicate to the effort.