Refactor Holes and Reifiers slices of Quasiquotes cake

This commit performs a number of preliminary refactoring needed to
implement unliftable:

1. Replace previous inheritance-heavy implementation of Holes with
   similar but much simpler one. Holes are now split into two different
   categories: ApplyHole and UnapplyHole which correspondingly represent
   information about holes in construction and deconstruction quasiquotes.

2. Make Placeholders extract holes rather than their field values. This
   is required to be able to get additional mode-specific information
   from holes (e.g. only ApplyHoles have types).

3. Bring ApplyReifier & UnapplyReifier even closer to the future where
   there is just a single base Reifier with mode parameter.

Along the way a few bugs were fixed:

1. SI-7980 SI-7996 fail with nice error on bottom types splices

2. Use asSeenFrom instead of typeArguments in parseCardinality.
   This fixes a crash if T <:< Iterable[Tree] but does not itself
   have any type arguments.

3. Fix spurious error message on splicing of Lists through Liftable[List[T]]

3 files changed, 29 insertions, 0 deletions

diff --git a/test/files/scalacheck/quasiquotes/ErrorProps.scala b/test/files/scalacheck/quasiquotes/ErrorProps.scala
index adad48fcdf..92d299bede 100644
--- a/test/files/scalacheck/quasiquotes/ErrorProps.scala
+++ b/test/files/scalacheck/quasiquotes/ErrorProps.scala
@@ -172,6 +172,20 @@ object ErrorProps extends QuasiquoteProperties("errors") {
       val q"$m1 $m2 def foo" = EmptyTree
     """)
 
+  property("can't splice values of Null") = fails(
+    "Can't splice Null, bottom type values often indicate programmer mistake",
+    """
+      val n = null
+      q"$n"
+    """)
+
+  property("can't splice values of Nothing") = fails(
+    "Can't splice Nothing, bottom type values often indicate programmer mistake",
+    """
+      def n = ???
+      q"$n"
+    """)
+
   // // Make sure a nice error is reported in this case
   // { import Flag._; val mods = NoMods; q"lazy $mods val x: Int" }
 }
\ No newline at end of file
diff --git a/test/files/scalacheck/quasiquotes/LiftableProps.scala b/test/files/scalacheck/quasiquotes/LiftableProps.scala
index 1271e1accd..2173337edd 100644
--- a/test/files/scalacheck/quasiquotes/LiftableProps.scala
+++ b/test/files/scalacheck/quasiquotes/LiftableProps.scala
@@ -76,4 +76,14 @@ object LiftableProps extends QuasiquoteProperties("liftable") {
     val const = Constant(0)
     assert(q"$const" ≈ q"0")
   }
+
+  property("lift list variants") = test {
+    val lst = List(1, 2)
+    val immutable = q"$scalapkg.collection.immutable"
+    assert(q"$lst" ≈ q"$immutable.List(1, 2)")
+    assert(q"f(..$lst)" ≈ q"f(1, 2)")
+    val llst = List(List(1), List(2))
+    assert(q"f(..$llst)" ≈ q"f($immutable.List(1), $immutable.List(2))")
+    assert(q"f(...$llst)" ≈ q"f(1)(2)")
+  }
 }
\ No newline at end of file
diff --git a/test/files/scalacheck/quasiquotes/TermConstructionProps.scala b/test/files/scalacheck/quasiquotes/TermConstructionProps.scala
index 338c379fc3..6fb05ff9a4 100644
--- a/test/files/scalacheck/quasiquotes/TermConstructionProps.scala
+++ b/test/files/scalacheck/quasiquotes/TermConstructionProps.scala
@@ -204,6 +204,11 @@ object TermConstructionProps extends QuasiquoteProperties("term construction") {
     assert(q"f(${if (true) q"a" else q"b"})" ≈ q"f(a)")
   }
 
+  property("splice iterable of non-parametric type") = test {
+    object O extends Iterable[Tree] { def iterator = List(q"foo").iterator }
+    q"f(..$O)"
+  }
+
   property("SI-8016") = test {
     val xs = q"1" :: q"2" :: Nil
     assertEqAst(q"..$xs", "{1; 2}")