1 files changed, 18 insertions, 5 deletions
diff --git a/src/library/scala/collection/MapLike.scala b/src/library/scala/collection/MapLike.scala
index 99ed67325c..4ac87b29a9 100644
--- a/src/library/scala/collection/MapLike.scala
+++ b/src/library/scala/collection/MapLike.scala
@@ -11,7 +11,7 @@ package collection
 
 import generic._
 import mutable.{ Builder, MapBuilder }
-import scala.annotation.{migration, bridge}
+import scala.annotation.migration
 import parallel.ParMap
 
 /** A template trait for maps, which associate keys with values.
@@ -230,11 +230,15 @@ self =>
   protected class FilteredKeys(p: A => Boolean) extends AbstractMap[A, B] with DefaultMap[A, B] {
     override def foreach[U](f: ((A, B)) => U): Unit = for (kv <- self) if (p(kv._1)) f(kv)
     def iterator = self.iterator.filter(kv => p(kv._1))
-    override def contains(key: A) = self.contains(key) && p(key)
+    override def contains(key: A) = p(key) && self.contains(key)
     def get(key: A) = if (!p(key)) None else self.get(key)
   }
 
   /** Filters this map by retaining only keys satisfying a predicate.
+   *
+   *  '''Note''': the predicate must accept any key of type `A`, not just those already
+   *  present in the map, as the predicate is tested before the underlying map is queried.
+   *
    *  @param  p   the predicate used to test keys
    *  @return an immutable map consisting only of those key value pairs of this map where the key satisfies
    *          the predicate `p`. The resulting map wraps the original map without copying any elements.
@@ -319,11 +323,20 @@ self =>
     res
   }
 
-  /* Overridden for efficiency. */
-  override def toSeq: Seq[(A, B)] = toBuffer[(A, B)]
+  override def toSeq: Seq[(A, B)] = {
+    if (isEmpty) Vector.empty[(A, B)]
+    else {
+      // Default appropriate for immutable collections; mutable collections override this
+      val vb = Vector.newBuilder[(A, B)]
+      foreach(vb += _)
+      vb.result
+    }
+  }
+
   override def toBuffer[C >: (A, B)]: mutable.Buffer[C] = {
     val result = new mutable.ArrayBuffer[C](size)
-    copyToBuffer(result)
+    // Faster to let the map iterate itself than to defer through copyToBuffer
+    foreach(result += _)
     result
   }