SI-6187 Make partial functions re-typable

 - `New(tpe)` doesn't survive a `resetAttrs` / typecheck; use
   a name instead.
 - Abandon the tree attachment that passed the default
   case from `typer` to `patmat`; this tree eluded the
   attribute reset performed in the macro. Instead, add it
   to the match. Apart from making the tree re-typable, it
   also exposes the true code structure to macros, which
   is important if they need to perform other code
   transformations.
 - Install original trees on the declared types of the
   parameters of the `applyOrElse` method to ensure that
   references to them within the method pick up the correct
   type parameter skolems upon retypechecking.
 - Propagate `TypeTree#original` through `copyAttrs`,
   which is called during tree duplication / `TreeCopiers`.
   Without this, the original trees that we installed were
   not visible anymore during `ResetAttrs`.

We are not able to reify partial functions yet -- the
particular sticking point is reification of the parentage
which is only available in the `ClassInfoType`.

4 files changed, 55 insertions, 25 deletions

diff --git a/test/files/run/idempotency-partial-functions.scala b/test/files/run/idempotency-partial-functions.scala
deleted file mode 100644
index dd5f1167f1..0000000000
--- a/test/files/run/idempotency-partial-functions.scala
+++ /dev/null
@@ -1,25 +0,0 @@
-import scala.reflect.runtime.universe._
-import scala.reflect.runtime.{currentMirror => cm}
-import scala.tools.reflect.{ToolBox, ToolBoxError}
-import scala.tools.reflect.Eval
-
-object Test extends App {
-  val partials = reify {
-    List((false,true)) collect { case (x,true) => x }
-  }
-  try {
-    println(partials.eval)
-  } catch {
-    case _: ToolBoxError => println("error!!")
-  }
-  try {
-    val tb = cm.mkToolBox()
-    val tpartials = tb.typeCheck(partials.tree)
-    println(tpartials)
-    val rtpartials = tb.resetAllAttrs(tpartials)
-    println(tb.eval(rtpartials))
-  } catch {
-    // this is the current behaviour, rather than the desired behavior; see SI-6187
-    case _: ToolBoxError => println("error!")
-  }
-}
\ No newline at end of file
diff --git a/test/files/run/t6187.check b/test/files/run/t6187.check
new file mode 100644
index 0000000000..c0ca02923b
--- /dev/null
+++ b/test/files/run/t6187.check
@@ -0,0 +1,32 @@
+Type in expressions to have them evaluated.
+Type :help for more information.
+
+scala> import language.experimental.macros, reflect.macros.Context
+import language.experimental.macros
+import reflect.macros.Context
+
+scala> def macroImpl[T: c.WeakTypeTag](c: Context)(t: c.Expr[T]): c.Expr[List[T]] = {
+  val r = c.universe.reify { List(t.splice) }
+  c.Expr[List[T]]( c.resetLocalAttrs(r.tree) )
+}
+macroImpl: [T](c: scala.reflect.macros.Context)(t: c.Expr[T])(implicit evidence$1: c.WeakTypeTag[T])c.Expr[List[T]]
+
+scala> def demo[T](t: T): List[T] = macro macroImpl[T]
+demo: [T](t: T)List[T]
+
+scala> def m[T](t: T): List[List[T]] =
+  demo( List((t,true)) collect { case (x,true) => x } )
+m: [T](t: T)List[List[T]]
+
+scala> m(List(1))
+res0: List[List[List[Int]]] = List(List(List(1)))
+
+scala> // Showing we haven't added unreachable warnings
+
+scala> List(1) collect { case x => x }
+res1: List[Int] = List(1)
+
+scala> List("") collect { case x => x }
+res2: List[String] = List("")
+
+scala> 
diff --git a/test/files/run/t6187.scala b/test/files/run/t6187.scala
new file mode 100644
index 0000000000..ae642917e7
--- /dev/null
+++ b/test/files/run/t6187.scala
@@ -0,0 +1,18 @@
+import scala.tools.partest.ReplTest
+
+object Test extends ReplTest {
+  override def code = """
+import language.experimental.macros, reflect.macros.Context
+def macroImpl[T: c.WeakTypeTag](c: Context)(t: c.Expr[T]): c.Expr[List[T]] = {
+  val r = c.universe.reify { List(t.splice) }
+  c.Expr[List[T]]( c.resetLocalAttrs(r.tree) )
+}
+def demo[T](t: T): List[T] = macro macroImpl[T]
+def m[T](t: T): List[List[T]] =
+  demo( List((t,true)) collect { case (x,true) => x } )
+m(List(1))
+// Showing we haven't added unreachable warnings
+List(1) collect { case x => x }
+List("") collect { case x => x }
+  """.trim
+}
diff --git a/test/files/run/t6187b.scala b/test/files/run/t6187b.scala
new file mode 100644
index 0000000000..d2d3e9797d
--- /dev/null
+++ b/test/files/run/t6187b.scala
@@ -0,0 +1,5 @@
+object Test extends App {
+  val x: PartialFunction[Int, Int] = { case 1 => 1 }
+  val o: Any = ""
+  assert(x.applyOrElse(0, (_: Int) => o) == "")
+}