Add half: keyword to Numeric#round

core/numeric.rbs

@@ -668,8 +668,8 @@ class Numeric
   # Numeric implements this by converting `self` to a Float and invoking
   # Float#round.
   #
-  def round: () -> Integer
-           | (Integer digits) -> Numeric
+  def round: (?half: round_mode) -> Integer
+           | (Integer digits, ?half: round_mode) -> Numeric
 
   # <!--
   #   rdoc-file=numeric.c

test/stdlib/Numeric_test.rb

@@ -66,4 +66,21 @@ def test_step
     assert_send_type '(to: Rational, by: Float) { (Float) -> void } -> Rational',
                      1, :step, to: 3r, by: 0.2 do |i| break_from_block i end
    end
+
+  class NumericWithToF < Numeric
+    def to_f = 2.5
+  end
+
+  def test_round
+    receiver = NumericWithToF.new
+
+    assert_send_type '() -> Integer',
+                     receiver, :round
+    assert_send_type '(half: :even) -> Integer',
+                     receiver, :round, half: :even
+    assert_send_type '(Integer) -> Numeric',
+                     receiver, :round, 1
+    assert_send_type '(Integer, half: :down) -> Numeric',
+                     receiver, :round, 1, half: :down
+  end
 end