Francesc Campoy (@campoy) in his talk mentions that Go 1.12 now supports running go run on directories and packages. But I didn't find any mentions of it in tip release notes. Maybe it should be added there?
$ go1 version
go version go1.11.5 linux/amd64
$ go1 help run
usage: go run [build flags] [-exec xprog] package [arguments...]
Run compiles and runs the named main Go package.
Typically the package is specified as a list of .go source files,
but it may also be an import path, file system path, or pattern
matching a single known package, as in 'go run .' or 'go run my/cmd'.