Regression test for JRUBY-5863.

spec/regression/JRUBY-5863_named_capture_crash_on_nil_in_compiler_spec.rb

@@ -0,0 +1,19 @@
+require 'rspec'
+require 'stringio'
+require 'zlib'
+
+describe 'JRUBY-6559: GZipReader rewind with buffered input' do
+  it "rewinds properly when the input is buffered internally" do
+    zio = StringIO.new
+    io = Zlib::GzipWriter.new zio
+    io.write 'aaaa'
+    io.finish
+    zio << "junk" # this is buffered by Zlib
+    zio.rewind
+
+    io = Zlib::GzipReader.new(zio)
+    io.read.should == 'aaaa'
+    io.rewind
+    io.read.should == 'aaaa'
+  end
+end