Ehi @tgamblin, I have no idea. I just copied what was there before to make it build. I don't even know why that is needed, I'm not very fluent in Java (and I'm not a lover :)).

First thing: why those env vars are needed?

I guess it would be cool to upstream the env var handling in order to avoid patching the java files... But I have no idea on where to start.

First thing: why those env vars are needed?

The environment variables are how Spack passes information to the compiler wrappers that it inserts into whatever build system is being used by the package (in this case Bazel). For example, some of the environment variables are used to augment a given compiler invocation to add -I and -L entries to dependencies that were installed by Spack.

is there a more standard way to pass environment variables through like this

@tgamblin Bazel is something of a special case. Some users implement patches for "in-flux" files using Spack's FileFilter. I'm inclined to say that just updating the patch is conceptually simpler, although if the Spack environment variables change, it means more work updating the patches. For now this seems acceptable.