docs.rs isn't able to generate crate documentation: https://docs.rs/crate/google-cloud/0.2.1. I can build the docs locally as a workaround with cargo doc --all-features.

The failed build logs indicate a "Read-only file system" error while running the build script, which indicates to me that the codegen in the build script should be disabled for doc.rs builds, if not all rustdoc builds.