Is there a migration path from Maven to Bazel?

In the two years since Ulf responded, there's been a few efforts to assist with maven to bazel migration. In particular, the Bazel team is creating a tool to assist with this: https://github.com/bazelbuild/migration-tooling

The tool generates expansive WORKSPACE files from a set of pom files or maven coordinates. In the ideal case, you can pass the path to your maven project, and then it will generate a bzl file you can load into the WORKSPACE file.

More commentary on how to manage external dependencies can be found here: https://bazel.build/versions/master/docs/external.html

I work on Bazel. No, as far as we know there is no such process. I wish.

We have been running some migrations from other build systems to Bazel; the evidence isn't conclusive, but it's difficult to even envision how an incremental process would look like. There are some scenarios where we can envision one build system generating configuration files for another (like gyp), but then you still need to switch wholesale.