package xsbt


 * Collection of hacks that make it possible for the compiler interface
 * to stay source compatible with Scala compiler 2.9, 2.10 and 2.11.
 * One common technique used in `Compat` class is use of implicit conversions to deal
 * with methods that got renamed or moved between different Scala compiler versions.
 * Let's pick a specific example. In Scala 2.9 and 2.10 there was a method called `toplevelClass`
 * defined on `Symbol`. In 2.10 that method has been deprecated and `enclosingTopLevelClass`
 * method has been introduce as a replacement. In Scala 2.11 the old `toplevelClass` method has
 * been removed. How can we pick the right version based on availability of those two methods?
 * We define an implicit conversion from Symbol to a class that contains both method definitions:
 *   implicit def symbolCompat(sym: Symbol): SymbolCompat = new SymbolCompat(sym)
 *   class SymbolCompat(sym: Symbol) {
 *     def enclosingTopLevelClass: Symbol = sym.toplevelClass
 *     def toplevelClass: Symbol =
 *       throw new RuntimeException("For source compatibility only: should not get here.")
 *   }
 * We assume that client code (code in compiler interface) should always call `enclosingTopLevelClass`
 * method. If we compile that code against 2.11 it will just directly link against method provided by
 * Symbol. However, if we compile against 2.9 or 2.10 `enclosingTopLevelClass` won't be found so the
 * implicit conversion defined above will kick in. That conversion will provide `enclosingTopLevelClass`
 * that simply forwards to the old `toplevelClass` method that is available in 2.9 and 2.10 so that
 * method will be called in the end. There's one twist: since `enclosingTopLevelClass` forwards to
 * `toplevelClass` which doesn't exist in 2.11! Therefore, we need to also define `toplevelClass`
 * that will be provided by an implicit conversion as well. However, we should never reach that method
 * at runtime if either `enclosingTopLevelClass` or `toplevelClass` is available on Symbol so this
 * is purely source compatibility stub.
 * The technique described above is used in several places below.
abstract class Compat
	val global: Global
	import global._
	val LocalChild = global.tpnme.LOCAL_CHILD
	val Nullary = global.NullaryMethodType
	val ScalaObjectClass = definitions.ScalaObjectClass

	private[this] final class MiscCompat
		// in 2.9, nme.LOCALCHILD was renamed to tpnme.LOCAL_CHILD
		def tpnme = nme
		def LOCALCHILD = sourceCompatibilityOnly

		// in 2.10, ScalaObject was removed
		def ScalaObjectClass = definitions.ObjectClass

		def NullaryMethodType = NullaryMethodTpe

		def MACRO = DummyValue

		// in 2.10, sym.moduleSuffix exists, but genJVM.moduleSuffix(Symbol) does not
		def moduleSuffix(sym: Symbol): String = sourceCompatibilityOnly
		// in 2.11 genJVM does not exist
		def genJVM = this
	// in 2.9, NullaryMethodType was added to Type
	object NullaryMethodTpe {
		def unapply(t: Type): Option[Type] = None

	protected implicit def symbolCompat(sym: Symbol): SymbolCompat = new SymbolCompat(sym)
	protected final class SymbolCompat(sym: Symbol) {
		// before 2.10, sym.moduleSuffix doesn't exist, but genJVM.moduleSuffix does
		def moduleSuffix = global.genJVM.moduleSuffix(sym)

		def enclosingTopLevelClass: Symbol = sym.toplevelClass
		def toplevelClass: Symbol = sourceCompatibilityOnly

	val DummyValue = 0
	def hasMacro(s: Symbol): Boolean =
		val MACRO = Flags.MACRO // will be DummyValue for versions before 2.10
		MACRO != DummyValue && s.hasFlag(MACRO)
	def moduleSuffix(s: Symbol): String = s.moduleSuffix

	private[this] def sourceCompatibilityOnly: Nothing = throw new RuntimeException("For source compatibility only: should not get here.")

	private[this] final implicit def miscCompat(n: AnyRef): MiscCompat = new MiscCompat

	object MacroExpansionOf {
		def unapply(tree: Tree): Option[Tree] = {

			// MacroExpansionAttachment (MEA) compatibility for 2.8.x and 2.9.x
			object Compat {
				class MacroExpansionAttachment(val original: Tree)

				// Trees have no attachments in 2.8.x and 2.9.x
				implicit def withAttachments(tree: Tree): WithAttachments = new WithAttachments(tree)
				class WithAttachments(val tree: Tree) {
					object EmptyAttachments {
						def all = Set.empty[Any]
					val attachments = EmptyAttachments
			import Compat._

			locally {
				// Wildcard imports are necessary since 2.8.x and 2.9.x don't have `MacroExpansionAttachment` at all
				import global._ // this is where MEA lives in 2.10.x

				// `original` has been renamed to `expandee` in 2.11.x
				implicit def withExpandee(att: MacroExpansionAttachment): WithExpandee = new WithExpandee(att)
				class WithExpandee(att: MacroExpansionAttachment) {
					def expandee: Tree = att.original

				locally {
					import analyzer._ // this is where MEA lives in 2.11.x
					tree.attachments.all.collect {
						case att: MacroExpansionAttachment => att.expandee
					} headOption