SBT should require a project/build.properties or some other mechanism to avoid assuming any directory is a valid project.

This is more of a nice to have (and I don’t think there is an issue on this), but if you start SBT in a folder which isn’t a valid SBT project, SBT should either delete the target folder on shutdown, or not create it in the first place

The former I think is more realistic. This just came out because I always have a habit of starting SBT in the wrong place, and it always leaves behind target folders.

[SethTisue]

I wouldn’t mind if I had to answer a “are you sure (y/n)?” type prompt before being able to proceed as @mdedetrich describes.

Such a prompt could also suggest sbt new as an alternative, as per discussion at #6772

[mdedetrich]

On another note, there are SBT tasks from SBT plugins that are out there that don’t need a SBT project to be relevant. A good example is https://github.com/xerial/sbt-sonatype, which provides a sonatypeRelease task that promotes all of your current sonatype libraries from staging to release (this doesn’t need to be done in any relevant SBT project)