addCommandAlias method for defining command aliases in build definiti…

…ons. fixes #388

main/Defaults.scala

@@ -1139,6 +1139,18 @@ trait BuildExtra extends BuildCommon
 {
 		import Defaults._
 
+	/** Defines an alias given by `name` that expands to `value`.
+	* This alias is defined globally after projects are loaded.
+	* The alias is undefined when projects are unloaded.
+	* Names are restricted to be either alphanumeric or completely symbolic.
+	* As an exception, '-' and '_' are allowed within an alphanumeric name.*/
+	def addCommandAlias(name: String, value: String): Seq[Setting[State => State]] =
+	{
+		val add = (s: State) => BasicCommands.addAlias(s, name, value)
+		val remove = (s: State) => BasicCommands.removeAlias(s, name)
+		def compose(setting: SettingKey[State => State], f: State => State) = setting in Global ~= (_ compose f)
+		Seq( compose(onLoad, add), compose(onUnload, remove) )
+	}
 	def addSbtPlugin(dependency: ModuleID): Setting[Seq[ModuleID]] =
 		libraryDependencies <+= (sbtBinaryVersion in update,scalaBinaryVersion in update) { (sbtV, scalaV) => sbtPluginExtra(dependency, sbtV, scalaV) }
 

sbt/src/sbt-test/actions/add-alias/A.scala

@@ -0,0 +1,3 @@
+object A extends App {
+  if(args(0).toBoolean) () else error("Fail")
+}

sbt/src/sbt-test/actions/add-alias/build.sbt

@@ -0,0 +1,2 @@
+addCommandAlias("demo-success", "run true") ++
+addCommandAlias("demo-failure", "run false")

sbt/src/sbt-test/actions/add-alias/test

@@ -0,0 +1,2 @@
+> demo-success
+-> demo-failure