Scala 2.10.1 compat: account for change in PartialFunction synthesis.

Since SI-6187, the default case of a partial function is now included in the tree.
Before, it was a tree attachment, conditionally inserted in the pattern matcher.

I had hoped that that change would allow us to do away with
`RestorePatternMatchingFunctions` altogether, but it seems that
we aren't so lucky.

Instead, I've adapted that transformer to account for the new scheme.

Author: retronym

src/main/scala/scala/async/TransformUtils.scala

@@ -274,18 +274,26 @@ private[async] final case class TransformUtils[C <: Context](c: C) {
   private object RestorePatternMatchingFunctions extends Transformer {
 
     import language.existentials
+    val DefaultCaseName: TermName = "defaultCase$"
 
     override def transform(tree: Tree): Tree = {
       val SYNTHETIC = (1 << 21).toLong.asInstanceOf[FlagSet]
       def isSynthetic(cd: ClassDef) = cd.mods hasFlag SYNTHETIC
 
+      /** Is this pattern node a synthetic catch-all case, added during PartialFuction synthesis before we know
+        * whether the user provided cases are exhaustive. */
+      def isSyntheticDefaultCase(cdef: CaseDef) = cdef match {
+        case CaseDef(Bind(DefaultCaseName, _), EmptyTree, _) => true
+        case _                                                => false
+      }
       tree match {
         case Block(
         (cd@ClassDef(_, _, _, Template(_, _, body))) :: Nil,
         Apply(Select(New(a), nme.CONSTRUCTOR), Nil)) if isSynthetic(cd) =>
           val restored = (body collectFirst {
             case DefDef(_, /*name.apply | */ name.applyOrElse, _, _, _, Match(_, cases)) =>
-              val transformedCases = super.transformStats(cases, currentOwner).asInstanceOf[List[CaseDef]]
+              val nonSyntheticCases = cases.takeWhile(cdef => !isSyntheticDefaultCase(cdef))
+              val transformedCases = super.transformStats(nonSyntheticCases, currentOwner).asInstanceOf[List[CaseDef]]
               Match(EmptyTree, transformedCases)
           }).getOrElse(c.abort(tree.pos, s"Internal Error: Unable to find original pattern matching cases in: $body"))
           restored

src/test/scala/scala/async/run/toughtype/ToughType.scala

@@ -37,28 +37,26 @@ class ToughTypeSpec {
     res._1 mustBe (Nil)
   }
 
-//  TODO 2.10.1
-//  @Test def patternMatchingPartialFunction() {
-//    import AsyncId.{await, async}
-//    async {
-//      await(1)
-//      val a = await(1)
-//      val f = { case x => x + a }: PartialFunction[Int, Int]
-//      await(f(2))
-//    } mustBe 3
-//  }
+  @Test def patternMatchingPartialFunction() {
+    import AsyncId.{await, async}
+    async {
+      await(1)
+      val a = await(1)
+      val f = { case x => x + a }: PartialFunction[Int, Int]
+      await(f(2))
+    } mustBe 3
+  }
 
-//  TODO 2.10.1
-//  @Test def patternMatchingPartialFunctionNested() {
-//    import AsyncId.{await, async}
-//    async {
-//      await(1)
-//      val neg1 = -1
-//      val a = await(1)
-//      val f = { case x => ({case x => neg1 * x}: PartialFunction[Int, Int])(x + a) }: PartialFunction[Int, Int]
-//      await(f(2))
-//    } mustBe -3
-//  }
+  @Test def patternMatchingPartialFunctionNested() {
+    import AsyncId.{await, async}
+    async {
+      await(1)
+      val neg1 = -1
+      val a = await(1)
+      val f = { case x => ({case x => neg1 * x}: PartialFunction[Int, Int])(x + a) }: PartialFunction[Int, Int]
+      await(f(2))
+    } mustBe -3
+  }
 
   @Test def patternMatchingFunction() {
     import AsyncId.{await, async}