implement to_a for endless ranges

Author: Nicolas Laurent

spec/ruby/core/array/to_a_spec.rb

@@ -21,4 +21,8 @@
     array = ArraySpecs.recursive_array
     array.to_a.should == array
   end
+
+  it "throws an exception for endless ranges" do
+    -> { (1..).to_a }.should raise_error(RangeError)
+  end
 end

src/main/java/org/truffleruby/core/range/RangeNodes.java

@@ -386,8 +386,8 @@ protected DynamicObject toA(DynamicObject range) {
             }
         }
 
-        @Specialization(guards = "isObjectRange(range)")
-        protected Object toA(VirtualFrame frame, DynamicObject range) {
+        @Specialization(guards = { "isObjectRange(range)",  "!isEndlessRange(getContext(), range)" })
+        protected Object boundedToA(VirtualFrame frame, DynamicObject range) {
             if (toAInternalCall == null) {
                 CompilerDirectives.transferToInterpreterAndInvalidate();
                 toAInternalCall = insert(CallDispatchHeadNode.createPrivate());
@@ -396,6 +396,13 @@ protected Object toA(VirtualFrame frame, DynamicObject range) {
             return toAInternalCall.call(range, "to_a_internal");
         }
 
+        @Specialization(guards = { "isObjectRange(range)",  "isEndlessRange(getContext(), range)" })
+        protected Object endlessToA(VirtualFrame frame, DynamicObject range) {
+            throw new RaiseException(getContext(), coreExceptions().rangeError(
+                    "cannot convert endless range to an array",
+                    this));
+        }
+
     }
 
     /**