Compile and Tests, single-module project, 4 CPU laptop, as measured by GNU time. The value shown is the real (wall clock) time spend on the process.
Sbt and pants are quickest, by using all CPUs to the fullest (making the system unusable during that time). Else not much change since 2016, bazel became a bit faster.
Several buildsystems recognize there is nothing to do.
For this case I added a small no-op change to one source file.
For this case I manually reverted the file to the state of the first build.