Fix Enumerable#each_cons and Enumerable#each_slice to return a receiver

Co-authored-by: Takashi Kokubun <takashikkbn@gmail.com>
Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>

enum.c

@@ -2961,11 +2961,11 @@ enum_each_slice_size(VALUE obj, VALUE args, VALUE eobj)
 
 /*
  *  call-seq:
- *    each_slice(n) { ... }  ->  nil
+ *    each_slice(n) { ... }  ->  self
  *    each_slice(n)          ->  enumerator
  *
  *  Calls the block with each successive disjoint +n+-tuple of elements;
- *  returns +nil+:
+ *  returns +self+:
  *
  *    a = []
  *    (1..10).each_slice(3) {|tuple| a.push(tuple) } # => nil
@@ -2997,7 +2997,7 @@ enum_each_slice(VALUE obj, VALUE n)
     ary = memo->v1;
     if (RARRAY_LEN(ary) > 0) rb_yield(ary);
 
-    return Qnil;
+    return obj;
 }
 
 static VALUE
@@ -3040,11 +3040,11 @@ enum_each_cons_size(VALUE obj, VALUE args, VALUE eobj)
 
 /*
  *  call-seq:
- *    each_cons(n) { ... } ->  nil
+ *    each_cons(n) { ... } ->  self
  *    each_cons(n)         ->  enumerator
  *
  *  Calls the block with each successive overlapped +n+-tuple of elements;
- *  returns +nil+:
+ *  returns +self+:
  *
  *    a = []
  *    (1..5).each_cons(3) {|element| a.push(element) } # => nil
@@ -3072,7 +3072,7 @@ enum_each_cons(VALUE obj, VALUE n)
     memo = MEMO_NEW(rb_ary_new2(size), dont_recycle_block_arg(arity), size);
     rb_block_call(obj, id_each, 0, 0, each_cons_i, (VALUE)memo);
 
-    return Qnil;
+    return obj;
 }
 
 static VALUE

spec/ruby/core/enumerable/each_cons_spec.rb

@@ -10,7 +10,7 @@ describe "Enumerable#each_cons" do
 
   it "passes element groups to the block" do
     acc = []
-    @enum.each_cons(3){|g| acc << g}.should be_nil
+    @enum.each_cons(3){|g| acc << g}
     acc.should == @in_threes
   end
 
@@ -27,7 +27,7 @@ describe "Enumerable#each_cons" do
 
   it "tries to convert n to an Integer using #to_int" do
     acc = []
-    @enum.each_cons(3.3){|g| acc << g}.should == nil
+    @enum.each_cons(3.3){|g| acc << g}
     acc.should == @in_threes
 
     obj = mock('to_int')

spec/ruby/core/enumerable/each_slice_spec.rb

@@ -10,7 +10,7 @@ describe "Enumerable#each_slice" do
 
   it "passes element groups to the block" do
     acc = []
-    @enum.each_slice(3){|g| acc << g}.should be_nil
+    @enum.each_slice(3){|g| acc << g}
     acc.should == @sliced
   end
 
@@ -27,7 +27,7 @@ describe "Enumerable#each_slice" do
 
   it "tries to convert n to an Integer using #to_int" do
     acc = []
-    @enum.each_slice(3.3){|g| acc << g}.should == nil
+    @enum.each_slice(3.3){|g| acc << g}
     acc.should == @sliced
 
     obj = mock('to_int')

test/ruby/test_enum.rb

@@ -731,6 +731,8 @@ class TestEnumerable < Test::Unit::TestCase
     ary.clear
     (1..10).each_slice(11) {|a| ary << a}
     assert_equal([[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]], ary)
+
+    assert_equal(1..10, (1..10).each_slice(3) { })
   end
 
   def test_each_cons
@@ -750,6 +752,8 @@ class TestEnumerable < Test::Unit::TestCase
     ary.clear
     (1..5).each_cons(6) {|a| ary << a}
     assert_empty(ary)
+
+    assert_equal(1..5, (1..5).each_cons(3) { })
   end
 
   def test_zip