Make Enumerator::Lazy#with_index be lazy

Previously, Enumerator::Lazy#with_index was not defined, so it
picked up the default implementation from Enumerator, which was
not lazy.

Based on earlier patch from nobu.

Fixes [Bug #7877]

1 files changed, 22 insertions, 0 deletions

diff --git a/test/ruby/test_lazy_enumerator.rb b/test/ruby/test_lazy_enumerator.rb
index e76a53e650..80977a0bbd 100644
--- a/test/ruby/test_lazy_enumerator.rb
+++ b/test/ruby/test_lazy_enumerator.rb
@@ -587,4 +587,26 @@ EOS
     assert_equal([4, 6, 6, 4, 0, 4], e.first(6))
     assert_equal([4, 6, 6, 4, 0, 4], e.first(6))
   end
+
+  def test_with_index
+    feature7877 = '[ruby-dev:47025] [Feature #7877]'
+    leibniz = ->(n) {
+      (0..Float::INFINITY).lazy.with_index {|i, j|
+        raise IndexError, "limit exceeded (#{n})" unless j < n
+        ((-1) ** j) / (2*i+1).to_f
+      }.take(n).reduce(:+)
+    }
+    assert_nothing_raised(IndexError, feature7877) {
+      assert_in_epsilon(Math::PI/4, leibniz[1000])
+    }
+
+    ary = (0..Float::INFINITY).lazy.with_index(2) {|i, j| [i-1, j] }.take(2).to_a
+    assert_equal([[-1, 2], [0, 3]], ary)
+
+    ary = (0..Float::INFINITY).lazy.with_index(2).take(2).to_a
+    assert_equal([[0, 2], [1, 3]], ary)
+
+    ary = (0..Float::INFINITY).lazy.with_index.take(2).to_a
+    assert_equal([[0, 0], [1, 1]], ary)
+  end
 end