SI-8466 fix quasiquote crash on recursively iterable unlifting

In order to handle unquoting quasiquotes needs to know if type is
iterable and whats the depth of the iterable nesting which is called
rank. (e.g. List[List[Tree]] is rank 2 iterable of Tree)

The logic that checks depth of iterable nesting didn't take a situation
where T is in fact Iterable[T] which caused infinite recursion in
stripIterable function.

In order to fix it stripIterable now always recurs no more than
non-optional limit times.

src/compiler/scala/tools/reflect/quasiquotes/Holes.scala

@@ -43,13 +43,13 @@ trait Holes { self: Quasiquotes =>
     tpe <:< NothingClass.tpe || tpe <:< NullClass.tpe
   private def extractIterableTParam(tpe: Type) =
     IterableTParam.asSeenFrom(tpe, IterableClass)
-  private def stripIterable(tpe: Type, limit: Option[Rank] = None): (Rank, Type) =
-    if (limit.map { _ == NoDot }.getOrElse { false }) (NoDot, tpe)
+  private def stripIterable(tpe: Type, limit: Rank = DotDotDot): (Rank, Type) =
+    if (limit == NoDot) (NoDot, tpe)
     else if (tpe != null && !isIterableType(tpe)) (NoDot, tpe)
     else if (isBottomType(tpe)) (NoDot, tpe)
     else {
       val targ = extractIterableTParam(tpe)
-      val (rank, innerTpe) = stripIterable(targ, limit.map { _.pred })
+      val (rank, innerTpe) = stripIterable(targ, limit.pred)
       (rank.succ, innerTpe)
     }
   private def iterableTypeFromRank(n: Rank, tpe: Type): Type = {
@@ -76,7 +76,7 @@ trait Holes { self: Quasiquotes =>
 
   class ApplyHole(annotatedRank: Rank, unquotee: Tree) extends Hole {
     val (strippedTpe, tpe): (Type, Type) = {
-      val (strippedRank, strippedTpe) = stripIterable(unquotee.tpe, limit = Some(annotatedRank))
+      val (strippedRank, strippedTpe) = stripIterable(unquotee.tpe, limit = annotatedRank)
       if (isBottomType(strippedTpe)) cantSplice()
       else if (isNativeType(strippedTpe)) {
         if (strippedRank != NoDot && !(strippedTpe <:< treeType) && !isLiftableType(strippedTpe)) cantSplice()
@@ -193,7 +193,7 @@ trait Holes { self: Quasiquotes =>
         val (iterableRank, _) = stripIterable(tpe)
         if (iterableRank.value < rank.value)
           c.abort(pat.pos, s"Can't extract $tpe with $rank, consider using $iterableRank")
-        val (_, strippedTpe) = stripIterable(tpe, limit = Some(rank))
+        val (_, strippedTpe) = stripIterable(tpe, limit = rank)
         if (strippedTpe <:< treeType) treeNoUnlift
         else
           unlifters.spawn(strippedTpe, rank).map {

test/files/scalacheck/quasiquotes/LiftableProps.scala

@@ -164,4 +164,11 @@ object LiftableProps extends QuasiquoteProperties("liftable") {
     val right3: Either[Int, Int] = Right(1)
     assert(q"$right3" ≈ q"scala.util.Right(1)")
   }
+
+  property("lift xml comment") = test {
+    implicit val liftXmlComment = Liftable[xml.Comment] { comment =>
+      q"new _root_.scala.xml.Comment(${comment.commentText})"
+    }
+    assert(q"${xml.Comment("foo")}" ≈ q"<!--foo-->")
+  }
 }

test/files/scalacheck/quasiquotes/UnliftableProps.scala

@@ -155,4 +155,12 @@ object UnliftableProps extends QuasiquoteProperties("unliftable") {
     assert(t21 == (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21))
     assert(t22 == (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22))
   }
+
+  property("unlift xml comment") = test {
+    implicit val unliftXmlComment = Unliftable[xml.Comment] {
+      case q"new _root_.scala.xml.Comment(${value: String})" => xml.Comment(value)
+    }
+    val q"${comment: xml.Comment}" = q"<!--foo-->"
+    assert(comment.commentText == "foo")
+  }
 }