Range#step returns correct ArithmeticSequence

CHANGELOG.md

@@ -10,6 +10,7 @@ Bug fixes:
 * Capture the intercepted feature path during patching to reuse during patch require (#2441).
 * Update `Module#constants` to filter invalid constant identifiers (#2452).
 * Fixed `-0.0 <=> 0.0` and `-0.0 <=> 0` to return `0` like on CRuby (#1391).
+* Fixed `Range#step` to return correct class with begin-less range (#2516)
 
 Compatibility:
 

spec/ruby/core/range/step_spec.rb

@@ -481,6 +481,24 @@
           end
         end
 
+        ruby_version_is "2.7" do
+          context "when begin is not defined and end is numeric" do
+            it "returns an instance of Enumerator::ArithmeticSequence" do
+              eval("..10").step.class.should == Enumerator::ArithmeticSequence
+            end
+          end
+        end
+
+        context "when range is endless" do
+          it "returns an instance of Enumerator::ArithmeticSequence when begin is numeric" do
+            (1..).step.class.should == Enumerator::ArithmeticSequence
+          end
+
+          it "returns an instance of Enumerator when begin is not numeric" do
+            ("a"..).step.class.should == Enumerator
+          end
+        end
+
         context "when begin and end are not numerics" do
           it "returns an instance of Enumerator" do
             ("a".."z").step.class.should == Enumerator

src/main/ruby/truffleruby/core/range.rb

@@ -442,7 +442,7 @@ def %(n)
 
   private def step_internal(step_size=1, &block) # :yields: object
 
-    if !block_given? && Primitive.object_kind_of?(self.begin, Numeric) && (Primitive.nil?(self.end) || Primitive.object_kind_of?(self.end, Numeric))
+    if !block_given? && (Primitive.nil?(self.begin) || Primitive.object_kind_of?(self.begin, Numeric)) && (Primitive.nil?(self.end) || Primitive.object_kind_of?(self.end, Numeric))
       return Enumerator::ArithmeticSequence.new(self, :step, self.begin, self.end, step_size, self.exclude_end?)
     end