Merge pull request #200 from szeiger/wip/fix-buildfrom

Upgrade BuildFrom to the latest definition from 2.13

compat/src/main/scala-2.11_2.12/scala/collection/compat/BuildFrom.scala

@@ -13,7 +13,7 @@
 package scala.collection.compat
 
 import scala.collection.generic.CanBuildFrom
-import scala.collection.{Iterable, mutable}
+import scala.collection.mutable
 
 /** Builds a collection of type `C` from elements of type `A` when a source collection of type `From` is available.
  * Implicit instances of `BuildFrom` are available for all collection types.
@@ -23,16 +23,14 @@ import scala.collection.{Iterable, mutable}
  * @tparam C Type of collection (e.g. `List[Int]`, `TreeMap[Int, String]`, etc.)
  */
 trait BuildFrom[-From, -A, +C] extends Any {
-
-  def fromSpecificIterable(from: From)(it: Iterable[A]): C
+  def fromSpecific(from: From)(it: IterableOnce[A]): C
 
   /** Get a Builder for the collection. For non-strict collection types this will use an intermediate buffer.
-   * Building collections with `fromSpecificIterable` is preferred because it can be lazy for lazy collections. */
+    * Building collections with `fromSpecific` is preferred because it can be lazy for lazy collections. */
   def newBuilder(from: From): mutable.Builder[A, C]
 
-  @deprecated("Use newBuilder instead of apply()", "2.13.0")
+  @deprecated("Use newBuilder() instead of apply()", "2.13.0")
   @`inline` def apply(from: From): mutable.Builder[A, C] = newBuilder(from)
-
 }
 
 object BuildFrom {
@@ -41,7 +39,7 @@ object BuildFrom {
   implicit def fromCanBuildFrom[From, A, C](
       implicit cbf: CanBuildFrom[From, A, C]): BuildFrom[From, A, C] =
     new BuildFrom[From, A, C] {
-      def fromSpecificIterable(from: From)(it: Iterable[A]): C = (cbf(from) ++= it).result()
+      def fromSpecific(from: From)(it: IterableOnce[A]): C = (cbf(from) ++= it).result()
       def newBuilder(from: From): mutable.Builder[A, C]        = cbf(from)
     }
 

compat/src/test/scala/test/scala/collection/BuildFromTest.scala

@@ -158,4 +158,10 @@ class BuildFromTest {
   Map: BuildFrom[_, (Int, String), Map[Int, String]]
   SortedSet: BuildFrom[_, Int, SortedSet[Int]]
   SortedMap: BuildFrom[_, (Int, String), SortedMap[Int, String]]
+
+  // Implement BuildFrom
+  class MyBuildFrom[From, A, C] extends BuildFrom[From, A, C] {
+    def fromSpecific(from: From)(it: IterableOnce[A]): C = ???
+    def newBuilder(from: From): Builder[A, C] = ???
+  }
 }