FR: Running the bazel tests with a custom configuration

[iirina]

The Java tools have been recently moved out of the bazel binary (see bazelbuild/bazel#6316) and are now released separately. However the Java tools need to maintain the same level of testing coverage as before. One idea is to introduce a new flag in Bazel that points to a Java tools archive and have a presubmit pipeline running all the bazel tests with the flag pointing to the Java tools archive built at head. Other ideas of keeping the same testing coverage are welcome.

cc: @fweikert

[philwo]

@iirina How could we point Bazel to another Java tools archive, if not with a flag? Modify a WORKSPACE file somehow, maybe?

I'm sure we can set this up, but I don't know what exactly you need and on which pipeline :)

[iirina]

A way to do this is to add the http_archive in the WORKSPACE file and then specify --java_toolchain=@java_tools//:toolchain as build flag (similar to how ubuntu1804_javabase9 and ubuntu1804_javabase10 are set up).

However, given that we have different java_tools releases for java 9, 10, 11 and soon 12, I'm not sure it scales to add this overhead on our CI. Maybe it's worth doing so on postsubmit. Wdyt?