Fix YAML serialization (#508)

Ref: #486

Following the introduction of `NONE` flags, `Addressable::URI`
instance can no longer be correctly serialized with YAML.

It appear to work, but `NONE` is serialized as `!ruby/object {}`,
so when the YAML is parsed back, the attributes are assigned a
distinct anonymous object.

Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

lib/addressable/uri.rb

@@ -2396,6 +2396,25 @@ def defer_validation
       @validation_deferred = false
     end
 
+    def encode_with(coder)
+      instance_variables.each do |ivar|
+        value = instance_variable_get(ivar)
+        if value != NONE
+          key = ivar.to_s.slice(1..-1)
+          coder[key] = value
+        end
+      end
+      nil
+    end
+
+    def init_with(coder)
+      reset_ivs
+      coder.map.each do |key, value|
+        instance_variable_set("@#{key}", value)
+      end
+      nil
+    end
+
   protected
     SELF_REF = '.'
     PARENT = '..'

spec/addressable/uri_spec.rb

@@ -20,6 +20,7 @@
 require "addressable/uri"
 require "uri"
 require "ipaddr"
+require "yaml"
 
 if !"".respond_to?("force_encoding")
   class String
@@ -6799,3 +6800,10 @@ def to_str
     expect(res).to be nil
   end
 end
+
+describe Addressable::URI, "YAML safe loading" do
+  it "doesn't serialize anonymous objects" do
+    url = Addressable::URI.parse("http://example.com/")
+    expect(YAML.dump(url)).to_not include("!ruby/object {}")
+  end
+end