SI-9126 Missing .seqs causes problems with parallel GenXs

Added `.seq` in two essential places so that a parallel collection passed as an argument won't mess up side-effecting sequential computations in `List.flatMap` and `GenericTraversableTemplate.transpose` (thanks to retronym for finding the danger spots).

Tests that `.seq` is called by constructing a `GenSeq` whose `.seq` disagrees with anything non-`.seq` (idea & working implementation from retronym).

Also updates the `.seq` test for `Vector#++` to use the new more efficient method.

2 files changed, 2 insertions, 2 deletions

diff --git a/src/library/scala/collection/generic/GenericTraversableTemplate.scala b/src/library/scala/collection/generic/GenericTraversableTemplate.scala
index 54455c531a..bdd91ba7a4 100644
--- a/src/library/scala/collection/generic/GenericTraversableTemplate.scala
+++ b/src/library/scala/collection/generic/GenericTraversableTemplate.scala
@@ -216,7 +216,7 @@ trait GenericTraversableTemplate[+A, +CC[X] <: GenTraversable[X]] extends HasNew
     val bs: IndexedSeq[Builder[B, CC[B]]] = IndexedSeq.fill(headSize)(genericBuilder[B])
     for (xs <- sequential) {
       var i = 0
-      for (x <- asTraversable(xs)) {
+      for (x <- asTraversable(xs).seq) {
         if (i >= headSize) fail
         bs(i) += x
         i += 1
diff --git a/src/library/scala/collection/immutable/List.scala b/src/library/scala/collection/immutable/List.scala
index a46b4adabb..254f14f13c 100644
--- a/src/library/scala/collection/immutable/List.scala
+++ b/src/library/scala/collection/immutable/List.scala
@@ -324,7 +324,7 @@ sealed abstract class List[+A] extends AbstractSeq[A]
         var h: ::[B] = null
         var t: ::[B] = null
         while (rest ne Nil) {
-          f(rest.head).foreach{ b =>
+          f(rest.head).seq.foreach{ b =>
             if (!found) {
               h = new ::(b, Nil)
               t = h