SI-7502 removing non-existent element from ListMap returns same map.

Current imperative version constructs a new ListMap regardless of
the fact the map doesn't contain the element. Replace it with the
tail-recursive variant that conserves. Also replace some usages with
the invariant now held.

1 files changed, 26 insertions, 0 deletions

diff --git a/test/files/run/list_map.scala b/test/files/run/list_map.scala
new file mode 100755
index 0000000000..fba3aae228
--- /dev/null
+++ b/test/files/run/list_map.scala
@@ -0,0 +1,26 @@
+import collection.immutable.ListMap
+
+object Test {
+  def testImmutableMinus() {
+    val empty = ListMap.empty[Int, Int]
+
+    val m0 = ListMap(1 -> 1, 2 -> 2)
+    val m1 = m0 - 3
+    assert (m1 eq m0)
+    val m2 = m0 - 1
+    assert (m2.size == 1)
+    val m3 = m2 - 2
+    assert (m3 eq empty)
+
+    val m4 = ListMap(1 -> 1, 2 -> 2, 3 -> 3)
+    val m5 = m4 - 1
+    assert (m5 == ListMap(2 -> 2, 3 -> 3))
+    assert (m5.toList == (2, 2)::(3, 3)::Nil)
+
+    assert ((empty - 1) eq empty)
+  }
+
+  def main(args: Array[String]) {
+    testImmutableMinus()
+  }
+}