Reasons for making this change:

Ignore the new .bsp/ directory that is created by sbt 1.4.0 and later.

Links to documentation supporting these rule changes:

https://www.scala-sbt.org/1.x/docs/Combined+Pages.html#Build+server+protocol+%28BSP%29+support

sbt 1.4.0 adds build server protocol (BSP) support, contributed by Scala Center. Main implementation was done by Adrien Piquerez (@adpi2) based on @eed3si9n’s prototype.

When sbt 1.4.0 starts, it will create a file named .bsp/sbt.json containing a machine-readable instruction on how to run sbt -bsp, which is a command line program that uses standard input and output to communicate to sbt server using build server protocol.

Confirmation from Adrien (the main implementer) that .bsp should be ignored: https://gitter.im/sbt/sbt?at=5fc34d888c7c4215bb9726ef