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>

1 files changed, 96 insertions, 0 deletions

diff --git a/spec/ruby/core/array/shared/slice.rb b/spec/ruby/core/array/shared/slice.rb
index 3b09fdcbc6..8fb33738b9 100644
--- a/spec/ruby/core/array/shared/slice.rb
+++ b/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