Fix Array#[] with ArithmeticSequence with negative steps (#5739)

* Fix Array#[] with ArithmeticSequence with negative steps

Previously, Array#[] when called with an ArithmeticSequence
with a negative step did not handle all cases correctly,
especially cases involving infinite ranges, inverted ranges,
and/or exclusive ends.

Fixes [Bug #18247]

* Add Array#slice tests for ArithmeticSequence with negative step to test_array

Add tests of rb_arithmetic_sequence_beg_len_step C-API function.

* Fix ext/-test-/arith_seq/beg_len_step/depend

* Rename local variables

* Fix a variable name

Co-authored-by: Kenta Murata <3959+mrkn@users.noreply.github.com>

array.c

@@ -1373,13 +1373,16 @@ ary_make_partial_step(VALUE ary, VALUE klass, long offset, long len, long step)
     const VALUE *values = RARRAY_CONST_PTR_TRANSIENT(ary);
     const long orig_len = len;
 
-    if ((step > 0 && step >= len) || (step < 0 && (step < -len))) {
+    if (step > 0 && step >= len) {
         VALUE result = ary_new(klass, 1);
         VALUE *ptr = (VALUE *)ARY_EMBED_PTR(result);
         RB_OBJ_WRITE(result, ptr, values[offset]);
         ARY_SET_EMBED_LEN(result, 1);
         return result;
     }
+    else if (step < 0 && step < -len) {
+        step = -len;
+    }
 
     long ustep = (step < 0) ? -step : step;
     len = (len + ustep - 1) / ustep;

enumerator.c

@@ -3802,6 +3802,13 @@ rb_arithmetic_sequence_beg_len_step(VALUE obj, long *begp, long *lenp, long *ste
     *stepp = step;
 
     if (step < 0) {
+        if (aseq.exclude_end && !NIL_P(aseq.end)) {
+            /* Handle exclusion before range reversal */
+            aseq.end = LONG2NUM(NUM2LONG(aseq.end) + 1);
+
+            /* Don't exclude the previous beginning */
+            aseq.exclude_end = 0;
+        }
         VALUE tmp = aseq.begin;
         aseq.begin = aseq.end;
         aseq.end = tmp;

ext/-test-/arith_seq/beg_len_step/beg_len_step.c

@@ -0,0 +1,19 @@
+#include "ruby/ruby.h"
+
+static VALUE
+arith_seq_s_beg_len_step(VALUE mod, VALUE obj, VALUE len, VALUE err)
+{
+  VALUE r;
+  long beg, len2, step;
+
+  r = rb_arithmetic_sequence_beg_len_step(obj, &beg, &len2, &step, NUM2LONG(len), NUM2INT(err));
+
+  return rb_ary_new_from_args(4, r, LONG2NUM(beg), LONG2NUM(len2), LONG2NUM(step));
+}
+
+void
+Init_beg_len_step(void)
+{
+    VALUE cArithSeq = rb_path2class("Enumerator::ArithmeticSequence");
+    rb_define_singleton_method(cArithSeq, "__beg_len_step__", arith_seq_s_beg_len_step, 3);
+}

ext/-test-/arith_seq/beg_len_step/depend

@@ -0,0 +1,161 @@
+# AUTOGENERATED DEPENDENCIES START
+beg_len_step.o: $(RUBY_EXTCONF_H)
+beg_len_step.o: $(arch_hdrdir)/ruby/config.h
+beg_len_step.o: $(hdrdir)/ruby/assert.h
+beg_len_step.o: $(hdrdir)/ruby/backward.h
+beg_len_step.o: $(hdrdir)/ruby/backward/2/assume.h
+beg_len_step.o: $(hdrdir)/ruby/backward/2/attributes.h
+beg_len_step.o: $(hdrdir)/ruby/backward/2/bool.h
+beg_len_step.o: $(hdrdir)/ruby/backward/2/inttypes.h
+beg_len_step.o: $(hdrdir)/ruby/backward/2/limits.h
+beg_len_step.o: $(hdrdir)/ruby/backward/2/long_long.h
+beg_len_step.o: $(hdrdir)/ruby/backward/2/stdalign.h
+beg_len_step.o: $(hdrdir)/ruby/backward/2/stdarg.h
+beg_len_step.o: $(hdrdir)/ruby/defines.h
+beg_len_step.o: $(hdrdir)/ruby/intern.h
+beg_len_step.o: $(hdrdir)/ruby/internal/abi.h
+beg_len_step.o: $(hdrdir)/ruby/internal/anyargs.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/char.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/double.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/fixnum.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/gid_t.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/int.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/intptr_t.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/long.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/long_long.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/mode_t.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/off_t.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/pid_t.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/short.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/size_t.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/st_data_t.h
+beg_len_step.o: $(hdrdir)/ruby/internal/arithmetic/uid_t.h
+beg_len_step.o: $(hdrdir)/ruby/internal/assume.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/alloc_size.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/artificial.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/cold.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/const.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/constexpr.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/deprecated.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/diagnose_if.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/enum_extensibility.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/error.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/flag_enum.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/forceinline.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/format.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/maybe_unused.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/noalias.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/nodiscard.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/noexcept.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/noinline.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/nonnull.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/noreturn.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/pure.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/restrict.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/returns_nonnull.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/warning.h
+beg_len_step.o: $(hdrdir)/ruby/internal/attr/weakref.h
+beg_len_step.o: $(hdrdir)/ruby/internal/cast.h
+beg_len_step.o: $(hdrdir)/ruby/internal/compiler_is.h
+beg_len_step.o: $(hdrdir)/ruby/internal/compiler_is/apple.h
+beg_len_step.o: $(hdrdir)/ruby/internal/compiler_is/clang.h
+beg_len_step.o: $(hdrdir)/ruby/internal/compiler_is/gcc.h
+beg_len_step.o: $(hdrdir)/ruby/internal/compiler_is/intel.h
+beg_len_step.o: $(hdrdir)/ruby/internal/compiler_is/msvc.h
+beg_len_step.o: $(hdrdir)/ruby/internal/compiler_is/sunpro.h
+beg_len_step.o: $(hdrdir)/ruby/internal/compiler_since.h
+beg_len_step.o: $(hdrdir)/ruby/internal/config.h
+beg_len_step.o: $(hdrdir)/ruby/internal/constant_p.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rarray.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rbasic.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rbignum.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rclass.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rdata.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rfile.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rhash.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/robject.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rregexp.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rstring.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rstruct.h
+beg_len_step.o: $(hdrdir)/ruby/internal/core/rtypeddata.h
+beg_len_step.o: $(hdrdir)/ruby/internal/ctype.h
+beg_len_step.o: $(hdrdir)/ruby/internal/dllexport.h
+beg_len_step.o: $(hdrdir)/ruby/internal/dosish.h
+beg_len_step.o: $(hdrdir)/ruby/internal/error.h
+beg_len_step.o: $(hdrdir)/ruby/internal/eval.h
+beg_len_step.o: $(hdrdir)/ruby/internal/event.h
+beg_len_step.o: $(hdrdir)/ruby/internal/fl_type.h
+beg_len_step.o: $(hdrdir)/ruby/internal/gc.h
+beg_len_step.o: $(hdrdir)/ruby/internal/glob.h
+beg_len_step.o: $(hdrdir)/ruby/internal/globals.h
+beg_len_step.o: $(hdrdir)/ruby/internal/has/attribute.h
+beg_len_step.o: $(hdrdir)/ruby/internal/has/builtin.h
+beg_len_step.o: $(hdrdir)/ruby/internal/has/c_attribute.h
+beg_len_step.o: $(hdrdir)/ruby/internal/has/cpp_attribute.h
+beg_len_step.o: $(hdrdir)/ruby/internal/has/declspec_attribute.h
+beg_len_step.o: $(hdrdir)/ruby/internal/has/extension.h
+beg_len_step.o: $(hdrdir)/ruby/internal/has/feature.h
+beg_len_step.o: $(hdrdir)/ruby/internal/has/warning.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/array.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/bignum.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/class.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/compar.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/complex.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/cont.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/dir.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/enum.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/enumerator.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/error.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/eval.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/file.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/gc.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/hash.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/io.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/load.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/marshal.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/numeric.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/object.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/parse.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/proc.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/process.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/random.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/range.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/rational.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/re.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/ruby.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/select.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/select/largesize.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/signal.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/sprintf.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/string.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/struct.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/thread.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/time.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/variable.h
+beg_len_step.o: $(hdrdir)/ruby/internal/intern/vm.h
+beg_len_step.o: $(hdrdir)/ruby/internal/interpreter.h
+beg_len_step.o: $(hdrdir)/ruby/internal/iterator.h
+beg_len_step.o: $(hdrdir)/ruby/internal/memory.h
+beg_len_step.o: $(hdrdir)/ruby/internal/method.h
+beg_len_step.o: $(hdrdir)/ruby/internal/module.h
+beg_len_step.o: $(hdrdir)/ruby/internal/newobj.h
+beg_len_step.o: $(hdrdir)/ruby/internal/rgengc.h
+beg_len_step.o: $(hdrdir)/ruby/internal/scan_args.h
+beg_len_step.o: $(hdrdir)/ruby/internal/special_consts.h
+beg_len_step.o: $(hdrdir)/ruby/internal/static_assert.h
+beg_len_step.o: $(hdrdir)/ruby/internal/stdalign.h
+beg_len_step.o: $(hdrdir)/ruby/internal/stdbool.h
+beg_len_step.o: $(hdrdir)/ruby/internal/symbol.h
+beg_len_step.o: $(hdrdir)/ruby/internal/value.h
+beg_len_step.o: $(hdrdir)/ruby/internal/value_type.h
+beg_len_step.o: $(hdrdir)/ruby/internal/variable.h
+beg_len_step.o: $(hdrdir)/ruby/internal/warning_push.h
+beg_len_step.o: $(hdrdir)/ruby/internal/xmalloc.h
+beg_len_step.o: $(hdrdir)/ruby/missing.h
+beg_len_step.o: $(hdrdir)/ruby/ruby.h
+beg_len_step.o: $(hdrdir)/ruby/st.h
+beg_len_step.o: $(hdrdir)/ruby/subst.h
+beg_len_step.o: beg_len_step.c
+# AUTOGENERATED DEPENDENCIES END

ext/-test-/arith_seq/beg_len_step/extconf.rb

@@ -0,0 +1,2 @@
+# frozen_string_literal: false
+create_makefile("-test-/arith_seq/beg_len_step")

spec/ruby/core/array/shared/slice.rb

@@ -784,6 +784,102 @@ describe :array_slice, shared: true do
     a.send(@method, (...-9)).should == []
   end
 
+  ruby_version_is "3.2" do
+    describe "can be sliced with Enumerator::ArithmeticSequence" do
+      it "with infinite/inverted ranges and negative steps" do
+        @array = [0, 1, 2, 3, 4, 5]
+        @array.send(@method, (2..).step(-1)).should == [2, 1, 0]
+        @array.send(@method, (2..).step(-2)).should == [2, 0]
+        @array.send(@method, (2..).step(-3)).should == [2]
+        @array.send(@method, (2..).step(-4)).should == [2]
+
+        @array.send(@method, (-3..).step(-1)).should == [3, 2, 1, 0]
+        @array.send(@method, (-3..).step(-2)).should == [3, 1]
+        @array.send(@method, (-3..).step(-3)).should == [3, 0]
+        @array.send(@method, (-3..).step(-4)).should == [3]
+        @array.send(@method, (-3..).step(-5)).should == [3]
+
+        @array.send(@method, (..0).step(-1)).should == [5, 4, 3, 2, 1, 0]
+        @array.send(@method, (..0).step(-2)).should == [5, 3, 1]
+        @array.send(@method, (..0).step(-3)).should == [5, 2]
+        @array.send(@method, (..0).step(-4)).should == [5, 1]
+        @array.send(@method, (..0).step(-5)).should == [5, 0]
+        @array.send(@method, (..0).step(-6)).should == [5]
+        @array.send(@method, (..0).step(-7)).should == [5]
+
+        @array.send(@method, (...0).step(-1)).should == [5, 4, 3, 2, 1]
+        @array.send(@method, (...0).step(-2)).should == [5, 3, 1]
+        @array.send(@method, (...0).step(-3)).should == [5, 2]
+        @array.send(@method, (...0).step(-4)).should == [5, 1]
+        @array.send(@method, (...0).step(-5)).should == [5]
+        @array.send(@method, (...0).step(-6)).should == [5]
+
+        @array.send(@method, (...1).step(-1)).should == [5, 4, 3, 2]
+        @array.send(@method, (...1).step(-2)).should == [5, 3]
+        @array.send(@method, (...1).step(-3)).should == [5, 2]
+        @array.send(@method, (...1).step(-4)).should == [5]
+        @array.send(@method, (...1).step(-5)).should == [5]
+
+        @array.send(@method, (..-5).step(-1)).should == [5, 4, 3, 2, 1]
+        @array.send(@method, (..-5).step(-2)).should == [5, 3, 1]
+        @array.send(@method, (..-5).step(-3)).should == [5, 2]
+        @array.send(@method, (..-5).step(-4)).should == [5, 1]
+        @array.send(@method, (..-5).step(-5)).should == [5]
+        @array.send(@method, (..-5).step(-6)).should == [5]
+
+        @array.send(@method, (...-5).step(-1)).should == [5, 4, 3, 2]
+        @array.send(@method, (...-5).step(-2)).should == [5, 3]
+        @array.send(@method, (...-5).step(-3)).should == [5, 2]
+        @array.send(@method, (...-5).step(-4)).should == [5]
+        @array.send(@method, (...-5).step(-5)).should == [5]
+
+        @array.send(@method, (4..1).step(-1)).should == [4, 3, 2, 1]
+        @array.send(@method, (4..1).step(-2)).should == [4, 2]
+        @array.send(@method, (4..1).step(-3)).should == [4, 1]
+        @array.send(@method, (4..1).step(-4)).should == [4]
+        @array.send(@method, (4..1).step(-5)).should == [4]
+
+        @array.send(@method, (4...1).step(-1)).should == [4, 3, 2]
+        @array.send(@method, (4...1).step(-2)).should == [4, 2]
+        @array.send(@method, (4...1).step(-3)).should == [4]
+        @array.send(@method, (4...1).step(-4)).should == [4]
+
+        @array.send(@method, (-2..1).step(-1)).should == [4, 3, 2, 1]
+        @array.send(@method, (-2..1).step(-2)).should == [4, 2]
+        @array.send(@method, (-2..1).step(-3)).should == [4, 1]
+        @array.send(@method, (-2..1).step(-4)).should == [4]
+        @array.send(@method, (-2..1).step(-5)).should == [4]
+
+        @array.send(@method, (-2...1).step(-1)).should == [4, 3, 2]
+        @array.send(@method, (-2...1).step(-2)).should == [4, 2]
+        @array.send(@method, (-2...1).step(-3)).should == [4]
+        @array.send(@method, (-2...1).step(-4)).should == [4]
+
+        @array.send(@method, (4..-5).step(-1)).should == [4, 3, 2, 1]
+        @array.send(@method, (4..-5).step(-2)).should == [4, 2]
+        @array.send(@method, (4..-5).step(-3)).should == [4, 1]
+        @array.send(@method, (4..-5).step(-4)).should == [4]
+        @array.send(@method, (4..-5).step(-5)).should == [4]
+
+        @array.send(@method, (4...-5).step(-1)).should == [4, 3, 2]
+        @array.send(@method, (4...-5).step(-2)).should == [4, 2]
+        @array.send(@method, (4...-5).step(-3)).should == [4]
+        @array.send(@method, (4...-5).step(-4)).should == [4]
+
+        @array.send(@method, (-2..-5).step(-1)).should == [4, 3, 2, 1]
+        @array.send(@method, (-2..-5).step(-2)).should == [4, 2]
+        @array.send(@method, (-2..-5).step(-3)).should == [4, 1]
+        @array.send(@method, (-2..-5).step(-4)).should == [4]
+        @array.send(@method, (-2..-5).step(-5)).should == [4]
+
+        @array.send(@method, (-2...-5).step(-1)).should == [4, 3, 2]
+        @array.send(@method, (-2...-5).step(-2)).should == [4, 2]
+        @array.send(@method, (-2...-5).step(-3)).should == [4]
+        @array.send(@method, (-2...-5).step(-4)).should == [4]
+      end
+    end
+  end
+
   it "can accept nil...nil ranges" do
     a = [0, 1, 2, 3, 4, 5]
     a.send(@method, eval("(nil...nil)")).should == a

test/-ext-/arith_seq/test_arith_seq_beg_len_step.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: false
+require 'test/unit'
+
+class Test_ArithSeq < Test::Unit::TestCase
+  def test_beg_len_step
+    assert_separately([], <<-"end;") #do
+      require '-test-/arith_seq/beg_len_step'
+
+      r, = Enumerator::ArithmeticSequence.__beg_len_step__([1, 2, 3], 0, 0)
+      assert_equal(false, r)
+
+      r, = Enumerator::ArithmeticSequence.__beg_len_step__([1, 2, 3], 1, 0)
+      assert_equal(false, r)
+
+      r, = Enumerator::ArithmeticSequence.__beg_len_step__([1, 2, 3], 3, 0)
+      assert_equal(false, r)
+
+      r, = Enumerator::ArithmeticSequence.__beg_len_step__(1..3, 0, 0)
+      assert_equal(nil, r)
+
+      r = Enumerator::ArithmeticSequence.__beg_len_step__(1..3, 1, 0)
+      assert_equal([true, 1, 0, 1], r)
+
+      r = Enumerator::ArithmeticSequence.__beg_len_step__(1..3, 2, 0)
+      assert_equal([true, 1, 1, 1], r)
+
+      r = Enumerator::ArithmeticSequence.__beg_len_step__(1..3, 3, 0)
+      assert_equal([true, 1, 2, 1], r)
+
+      r = Enumerator::ArithmeticSequence.__beg_len_step__(1..3, 4, 0)
+      assert_equal([true, 1, 3, 1], r)
+
+      r = Enumerator::ArithmeticSequence.__beg_len_step__(1..3, 5, 0)
+      assert_equal([true, 1, 3, 1], r)
+
+      r = Enumerator::ArithmeticSequence.__beg_len_step__((-10..10).step(2), 24, 0)
+      assert_equal([true, 14, 0, 2], r)
+
+      r = Enumerator::ArithmeticSequence.__beg_len_step__((-10..10).step(3), 24, 0)
+      assert_equal([true, 14, 0, 3], r)
+
+      r = Enumerator::ArithmeticSequence.__beg_len_step__((-10..10).step(3), 22, 0)
+      assert_equal([true, 12, 0, 3], r)
+
+      r = Enumerator::ArithmeticSequence.__beg_len_step__((-10..10).step(-3), 22, 0)
+      assert_equal([true, 10, 3, -3], r)
+
+      r = Enumerator::ArithmeticSequence.__beg_len_step__(1..3, 0, 1)
+      assert_equal([true, 1, 3, 1], r)
+    end;
+  end
+end

test/ruby/test_array.rb

@@ -1580,6 +1580,96 @@ class TestArray < Test::Unit::TestCase
     assert_equal_instance(a.values_at(*idx), a.slice((3..90)%2))
     idx = 90.step(3, -2).to_a
     assert_equal_instance(a.values_at(*idx), a.slice((90 .. 3)% -2))
+
+    a = [0, 1, 2, 3, 4, 5]
+    assert_equal([2, 1, 0], a.slice((2..).step(-1)))
+    assert_equal([2, 0], a.slice((2..).step(-2)))
+    assert_equal([2], a.slice((2..).step(-3)))
+    assert_equal([2], a.slice((2..).step(-4)))
+
+    assert_equal([3, 2, 1, 0], a.slice((-3..).step(-1)))
+    assert_equal([3, 1], a.slice((-3..).step(-2)))
+    assert_equal([3, 0], a.slice((-3..).step(-3)))
+    assert_equal([3], a.slice((-3..).step(-4)))
+    assert_equal([3], a.slice((-3..).step(-5)))
+
+    assert_equal([5, 4, 3, 2, 1, 0], a.slice((..0).step(-1)))
+    assert_equal([5, 3, 1], a.slice((..0).step(-2)))
+    assert_equal([5, 2], a.slice((..0).step(-3)))
+    assert_equal([5, 1], a.slice((..0).step(-4)))
+    assert_equal([5, 0], a.slice((..0).step(-5)))
+    assert_equal([5], a.slice((..0).step(-6)))
+    assert_equal([5], a.slice((..0).step(-7)))
+
+    assert_equal([5, 4, 3, 2, 1], a.slice((...0).step(-1)))
+    assert_equal([5, 3, 1], a.slice((...0).step(-2)))
+    assert_equal([5, 2], a.slice((...0).step(-3)))
+    assert_equal([5, 1], a.slice((...0).step(-4)))
+    assert_equal([5], a.slice((...0).step(-5)))
+    assert_equal([5], a.slice((...0).step(-6)))
+
+    assert_equal([5, 4, 3, 2], a.slice((...1).step(-1)))
+    assert_equal([5, 3], a.slice((...1).step(-2)))
+    assert_equal([5, 2], a.slice((...1).step(-3)))
+    assert_equal([5], a.slice((...1).step(-4)))
+    assert_equal([5], a.slice((...1).step(-5)))
+
+    assert_equal([5, 4, 3, 2, 1], a.slice((..-5).step(-1)))
+    assert_equal([5, 3, 1], a.slice((..-5).step(-2)))
+    assert_equal([5, 2], a.slice((..-5).step(-3)))
+    assert_equal([5, 1], a.slice((..-5).step(-4)))
+    assert_equal([5], a.slice((..-5).step(-5)))
+    assert_equal([5], a.slice((..-5).step(-6)))
+
+    assert_equal([5, 4, 3, 2], a.slice((...-5).step(-1)))
+    assert_equal([5, 3], a.slice((...-5).step(-2)))
+    assert_equal([5, 2], a.slice((...-5).step(-3)))
+    assert_equal([5], a.slice((...-5).step(-4)))
+    assert_equal([5], a.slice((...-5).step(-5)))
+
+    assert_equal([4, 3, 2, 1], a.slice((4..1).step(-1)))
+    assert_equal([4, 2], a.slice((4..1).step(-2)))
+    assert_equal([4, 1], a.slice((4..1).step(-3)))
+    assert_equal([4], a.slice((4..1).step(-4)))
+    assert_equal([4], a.slice((4..1).step(-5)))
+
+    assert_equal([4, 3, 2], a.slice((4...1).step(-1)))
+    assert_equal([4, 2], a.slice((4...1).step(-2)))
+    assert_equal([4], a.slice((4...1).step(-3)))
+    assert_equal([4], a.slice((4...1).step(-4)))
+
+    assert_equal([4, 3, 2, 1], a.slice((-2..1).step(-1)))
+    assert_equal([4, 2], a.slice((-2..1).step(-2)))
+    assert_equal([4, 1], a.slice((-2..1).step(-3)))
+    assert_equal([4], a.slice((-2..1).step(-4)))
+    assert_equal([4], a.slice((-2..1).step(-5)))
+
+    assert_equal([4, 3, 2], a.slice((-2...1).step(-1)))
+    assert_equal([4, 2], a.slice((-2...1).step(-2)))
+    assert_equal([4], a.slice((-2...1).step(-3)))
+    assert_equal([4], a.slice((-2...1).step(-4)))
+
+    assert_equal([4, 3, 2, 1], a.slice((4..-5).step(-1)))
+    assert_equal([4, 2], a.slice((4..-5).step(-2)))
+    assert_equal([4, 1], a.slice((4..-5).step(-3)))
+    assert_equal([4], a.slice((4..-5).step(-4)))
+    assert_equal([4], a.slice((4..-5).step(-5)))
+
+    assert_equal([4, 3, 2], a.slice((4...-5).step(-1)))
+    assert_equal([4, 2], a.slice((4...-5).step(-2)))
+    assert_equal([4], a.slice((4...-5).step(-3)))
+    assert_equal([4], a.slice((4...-5).step(-4)))
+
+    assert_equal([4, 3, 2, 1], a.slice((-2..-5).step(-1)))
+    assert_equal([4, 2], a.slice((-2..-5).step(-2)))
+    assert_equal([4, 1], a.slice((-2..-5).step(-3)))
+    assert_equal([4], a.slice((-2..-5).step(-4)))
+    assert_equal([4], a.slice((-2..-5).step(-5)))
+
+    assert_equal([4, 3, 2], a.slice((-2...-5).step(-1)))
+    assert_equal([4, 2], a.slice((-2...-5).step(-2)))
+    assert_equal([4], a.slice((-2...-5).step(-3)))
+    assert_equal([4], a.slice((-2...-5).step(-4)))
   end
 
   def test_slice_out_of_range