Ruby 2.7: Better support of Integer#[] with range arguments

spec/ruby/core/integer/element_reference_spec.rb

@@ -131,16 +131,10 @@
           0b000001[-3, 4].should == 0b1000
         end
 
-        it "ignores negative upper boundary" do
-          0b101001101[1..-1].should == 0b10100110
-          0b101001101[1..-2].should == 0b10100110
-          0b101001101[1..-3].should == 0b10100110
-        end
-
         it "ignores upper boundary smaller than lower boundary" do
           0b101001101[4..1].should == 0b10100
           0b101001101[4..2].should == 0b10100
-          0b101001101[4..3].should == 0b10100
+          0b101001101[-4..-5].should == 0b1010011010000
         end
 
         it "raises FloatDomainError if any boundary is infinity" do

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

@@ -38,6 +38,7 @@
 Object.deprecate_constant :Fixnum, :Bignum
 
 class Integer < Numeric
+  FIXNUM_MAX = 0x3fffffff
 
   # Have a copy in Integer of the Numeric version, as MRI does
   alias_method :remainder, :remainder
@@ -59,9 +60,57 @@ def **(o)
     redo_coerced :**, o
   end
 
-  def [](index)
+  def [](index, len = undefined)
+    if index.kind_of?(Range)
+      handle_range(index)
+    else
+      handle_aref(index, len)
+    end
+  end
+
+  private def handle_aref(index, len)
     index = Primitive.rb_to_int(index)
-    index < 0 ? 0 : (self >> index) & 1
+    if Primitive.undefined?(len)
+      index < 0 ? 0 : (self >> index) & 1
+    else
+      num = self >> index
+      mask = (1 << len) - 1
+
+      num & mask
+    end
+  end
+
+  private def handle_range(range)
+    validate_range(range)
+
+    if !Primitive.nil?(range.begin) && !Primitive.nil?(range.end)
+      len = range.end - range.begin
+      num = self >> range.begin
+      mask = mask(range, len)
+
+      range.end < range.begin ? num : num & mask
+    elsif Primitive.nil? range.end
+
+      return self >> range.begin
+    else
+      result = self & mask(range, range.end)
+      raise ArgumentError, 'The beginless range for Integer#[] results in infinity' if result != 0 && range.end >= 0
+
+      0
+    end
+  end
+
+  private def validate_range(index)
+    raise FloatDomainError , 'Infinity' if index.begin == Float::INFINITY || index.end == Float::INFINITY
+    raise FloatDomainError , '-Infinity' if index.begin == -Float::INFINITY || index.end == -Float::INFINITY
+  end
+
+  private def mask(range, idx)
+    if range.exclude_end?
+      (1 << idx) - 1
+    else
+      (1 << (idx +1)) - 1
+    end
   end
 
   def allbits?(mask)

test/mri/excludes/TestInteger.rb

@@ -11,5 +11,4 @@
 exclude :test_floor, "needs investigation"
 exclude :test_pow, "needs investigation"
 exclude :test_truncate, "needs investigation"
-exclude :test_Integer_with_invalid_exception, "needs investigation"
-exclude :test_aref, "needs investigation"
+exclude :test_Integer_with_invalid_exception, "needs investigation"