SI-6455 util.Try supports withFilter

src/library/scala/util/Try.scala

@@ -111,6 +111,35 @@ sealed abstract class Try[+T] {
    */
   def filter(p: T => Boolean): Try[T]
 
+  /** Creates a non-strict filter, which eventually converts this to a `Failure`
+   *  if the predicate is not satisfied.
+   *
+   *  Note: unlike filter, withFilter does not create a new Try.
+   *        Instead, it restricts the domain of subsequent
+   *        `map`, `flatMap`, `foreach`, and `withFilter` operations.
+   *
+   * As Try is a one-element collection, this may be a bit overkill,
+   * but it's consistent with withFilter on Option and the other collections.
+   *
+   *  @param p   the predicate used to test elements.
+   *  @return    an object of class `WithFilter`, which supports
+   *             `map`, `flatMap`, `foreach`, and `withFilter` operations.
+   *             All these operations apply to those elements of this Try
+   *             which satisfy the predicate `p`.
+   */
+  @inline final def withFilter(p: T => Boolean): WithFilter = new WithFilter(p)
+
+  /** We need a whole WithFilter class to honor the "doesn't create a new
+   *  collection" contract even though it seems unlikely to matter much in a
+   *  collection with max size 1.
+   */
+  class WithFilter(p: T => Boolean) {
+    def map[U](f:     T => U): Try[U]           = Try.this filter p map f
+    def flatMap[U](f: T => Try[U]): Try[U]      = Try.this filter p flatMap f
+    def foreach[U](f: T => U): Unit             = Try.this filter p foreach f
+    def withFilter(q: T => Boolean): WithFilter = new WithFilter(x => p(x) && q(x))
+  }
+
   /**
    * Applies the given function `f` if this is a `Failure`, otherwise returns this if this is a `Success`.
    * This is like `flatMap` for the exception.

test/junit/scala/util/TryTest.scala

@@ -0,0 +1,35 @@
+package scala.util
+
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+import org.junit.Test
+import org.junit.Assert._
+
+/* Test Try's withFilter method, which was added along with the -Xfuture fix for SI-6455  */
+@RunWith(classOf[JUnit4])
+class TryTest {
+  @Test
+  def withFilterFail(): Unit = {
+    val fail = for (x <- util.Try(1) if x > 1) yield x
+    assert(fail.isFailure)
+  }
+
+  @Test
+  def withFilterSuccess(): Unit = {
+    val success1 = for (x <- util.Try(1) if x >= 1) yield x
+    assertEquals(success1, util.Success(1))
+  }
+
+  @Test
+  def withFilterFlatMap(): Unit = {
+    val successFlatMap = for (x <- util.Try(1) if x >= 1; y <- util.Try(2) if x < y) yield x
+    assertEquals(successFlatMap, util.Success(1))
+  }
+
+  @Test
+  def withFilterForeach(): Unit = {
+    var ok = false
+    for (x <- util.Try(1) if x == 1) ok = x == 1
+    assert(ok)
+  }
+}