extra component for supporting dynamic changes to sbt's classpath. fixes #83

launch/Launch.scala

@@ -184,6 +184,8 @@ class ComponentProvider(baseDirectory: File, lockBoot: Boolean) extends xsbti.Co
 		else
 			Copy(files.toList, location)
 	}
+	def addToComponent(id: String, files: Array[File]): Boolean =
+		Copy(files.toList, componentLocation(id))
 	def lockFile = if(lockBoot) ComponentProvider.lockFile(baseDirectory) else null // null for the Java interface
 }
 object ComponentProvider

launch/Using.scala

@@ -13,15 +13,21 @@ object Using
 
 object Copy
 {
-	def apply(files: List[File], toDirectory: File): Unit =  files.foreach(file => apply(file, toDirectory))
-	def apply(file: File, toDirectory: File)
+	def apply(files: List[File], toDirectory: File): Boolean = files.map(file => apply(file, toDirectory)).contains(true)
+	def apply(file: File, toDirectory: File): Boolean =
 	{
 		toDirectory.mkdirs()
-		Using(new FileInputStream(file)) { in =>
-			Using(new FileOutputStream(new File(toDirectory, file.getName))) { out =>
-				transfer(in, out)
+		val to = new File(toDirectory, file.getName)
+		val missing = !to.exists
+		if(missing)
+		{
+			Using(new FileInputStream(file)) { in =>
+				Using(new FileOutputStream(to)) { out =>
+					transfer(in, out)
+				}
 			}
 		}
+		missing
 	}
 	def transfer(in: InputStream, out: OutputStream)
 	{

launch/interface/src/main/java/xsbti/ComponentProvider.java

@@ -4,8 +4,10 @@ import java.io.File;
 
 public interface ComponentProvider
 {
+	public File componentLocation(String id);
 	public File[] component(String componentID);
 	public void defineComponent(String componentID, File[] components);
+	public boolean addToComponent(String componentID, File[] components);
 	 // null if locking disabled
 	public File lockFile();
 }

launch/src/main/input_resources/sbt/sbt.boot.properties

@@ -6,7 +6,7 @@
   name: sbt
   version: read(sbt.version)[${{sbt.version}}]
   class: ${sbt.main.class-sbt.xMain}
-  components: xsbti
+  components: xsbti,extra
   cross-versioned: true
 
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