Oh, and don't forget that #Google donated $1,000,000 last year with a more narrow target: Rust and C++ interoperability: https://rustfoundation.org/media/google-contributes-1m-to-rust-foundation-to-support-c-rust-interop-initiative/.
When I was at Google, I had a lot of fun writing #Rust and calling into it from #Cpp with #Crubit. It supports bi-directional interop between the two languages, for some subset of both. See https://github.com/google/crubit if you're interested, though I don't actually know if this builds in the open without using #Bazel.