How do I enable multiple watch sources in sbt?

Question

I am trying to adapt this react-play seed repo . It contains the following code in build.sbt :

lazy val root = (project in file(".")).enablePlugins(PlayJava).settings(
  watchSources ++= (baseDirectory.value / "public/ui" ** "*").get
)

I would like to add another directory to watch. How do I do this? I tried variations on:

lazy val root = (project in file(".")).enablePlugins(PlayJava).settings(
  watchSources ++= (baseDirectory.value / "public/ui" ** "*").get;
  watchSources ++= (baseDirectory.value / "public2/ui" ** "*").get
)

The ++= leads me to think that the term on the right is a sequence of some sort, but I don't see how to add another directory to it. The above does not work - I get: ')' expected but ';' found. ')' expected but ';' found.

Answer 1

Use a comma instead of a semicolon. ++= produces a Setting ; it doesn't actually mutate anything. You can pass many of these to the method settings (via varargs), and like any other parameters you use commas.