The whole sourcepath in the form of one String.
Returns the class file and / or source file for a given external name, e.g., "java.lang.String". If there is both a class file and source file, the compiler can decide whether to read the class file or compile the source file.
Internally this seems to be used only by
ScriptRunner, but only to call
could probably be implemented differently.
Externally, it is used by sbt's compiler interface: https://github.com/sbt/sbt/blob/v0.13.15/compile/interface/src/main/scala/xsbt/CompilerInterface.scala#L249 Jason has some improvements for that in the works (https://github.com/scala/bug/issues/10289#issuecomment-310022699)