Prefer the registry over /etc/resolv.conf on native Windows

lib/resolv.rb

@@ -1132,14 +1132,15 @@ def Config.parse_resolv_conf(filename)
       end
 
       def Config.default_config_hash(filename="/etc/resolv.conf")
-        if File.exist? filename
-          Config.parse_resolv_conf(filename)
-        elsif defined?(Win32::Resolv)
+        # Native Windows resolves the path against the current drive, while Cygwin's own resolver honors it.
+        if defined?(Win32::Resolv) and !(/cygwin/ =~ RUBY_PLATFORM and File.exist?(filename))
           search, nameserver = Win32::Resolv.get_resolv_info
           config_hash = {}
           config_hash[:nameserver] = nameserver if nameserver
           config_hash[:search] = [search].flatten if search
           config_hash
+        elsif File.exist? filename
+          Config.parse_resolv_conf(filename)
         else
           {}
         end

test/resolv/test_win32_config.rb

@@ -2,6 +2,7 @@
 
 require 'test/unit'
 require 'resolv'
+require 'tempfile'
 
 # JRuby loads its bundled win32/resolv, which lacks the registry access of the extension.
 if defined?(Win32::Resolv) && Win32::Resolv.respond_to?(:tcpip_params, true)
@@ -23,5 +24,18 @@ def test_nonexistent_key
     def test_nonexistent_value
       assert_nil(Win32::Resolv.send(:tcpip_params) {|reg| reg.value('NonExistentKeyThatShouldNotExist')})
     end
+
+    def test_default_config_hash_with_resolv_conf
+      Tempfile.create("resolv.conf") do |f|
+        f.puts "nameserver 192.0.2.1"
+        f.close
+        nameserver = Resolv::DNS::Config.default_config_hash(f.path)[:nameserver]
+        if /cygwin/ =~ RUBY_PLATFORM
+          assert_equal(["192.0.2.1"], nameserver)
+        else
+          assert_not_include(Array(nameserver), "192.0.2.1")
+        end
+      end
+    end
   end
 end