Environment

jruby -v: jruby 9.2.0.0 (2.5.0) 2018-05-24 81156a8 Java HotSpot(TM) 64-Bit Server VM 25.102-b14 on 1.8.0_102-b14 +jit [darwin-x86_64]

uname -a: Darwin ..... 17.7.0 Darwin Kernel Version 17.7.0: Thu Jun 21 22:53:14 PDT 2018; root:xnu-4570.71.2~1/RELEASE_X86_64 x86_64

Expected Behavior

I believe this is related to (and an acknowledged caveat of) #4410; I have an Enumerator of an uncertain size, but sometimes contains only a single element. In MRI ruby, when I call slice_when (or chunk_when), I get:

def a
  return self.enum_for(:a) unless block_given?
  yield 1
end

a.slice_when { true }.to_a # => [[1]]

Actual Behavior

In JRuby 9.2.0.0, the single element in not returned:

def a
  return self.enum_for(:a) unless block_given?
  yield 1
end

a.slice_when { true }.to_a # => [[]]