Oj 2 and 3 support

By using dynamic definition, we can support both versions with only
tiny cost at start-up.  Oj3 has made its option hash more like the
JSON gem's, but duplicate "by hand" the "pretty" option hash as it's
small and slow-changing enough, and to avoid surprises with new Ruby
versions.

.travis.yml

@@ -23,28 +23,28 @@ matrix:
     dist: trusty
     env: SKIP_ADAPTERS=oj,yajl,nsjsonserialization
   - rvm: 2.0
-    gemfile: gemfiles/gemfile-2
+    gemfile: gemfiles/gemfile-2-0
     env: SKIP_ADAPTERS=gson,jr_jackson,nsjsonserialization
   - rvm: 2.1
-    gemfile: gemfiles/gemfile-2
+    gemfile: gemfiles/gemfile-2-0
     env: SKIP_ADAPTERS=gson,jr_jackson,nsjsonserialization
   - rvm: 2.2
-    gemfile: gemfiles/gemfile-2
+    gemfile: gemfiles/gemfile-2-0
     env: SKIP_ADAPTERS=gson,jr_jackson,nsjsonserialization
   - rvm: 2.3
-    gemfile: gemfiles/gemfile-2
+    gemfile: gemfiles/gemfile-2-3
     env: SKIP_ADAPTERS=gson,jr_jackson,nsjsonserialization
   - rvm: 2.4
-    gemfile: gemfiles/gemfile-2
+    gemfile: gemfiles/gemfile-2-3
     env: SKIP_ADAPTERS=gson,jr_jackson,nsjsonserialization
   - rvm: 2.5
-    gemfile: gemfiles/gemfile-2
+    gemfile: gemfiles/gemfile-2-3
     env: SKIP_ADAPTERS=gson,jr_jackson,nsjsonserialization
   - rvm: 2.6
-    gemfile: gemfiles/gemfile-2
+    gemfile: gemfiles/gemfile-2-3
     env: SKIP_ADAPTERS=gson,jr_jackson,nsjsonserialization
   - rvm: ruby-head
-    gemfile: gemfiles/gemfile-2
+    gemfile: gemfiles/gemfile-2-3
     env: SKIP_ADAPTERS=gson,jr_jackson,nsjsonserialization
   - rvm: jruby-9000
     gemfile: gemfiles/gemfile-2-jruby

gemfiles/gemfile-2 → gemfiles/gemfile-2-0

@@ -2,7 +2,7 @@ source "https://rubygems.org"
 
 gem "json",      "~> 2.0",  require: false
 gem "json_pure", "~> 2.0",  require: false
-gem "oj",        "~> 2.18", require: false
+gem "oj",        "~> 2.0",  require: false
 gem "yajl-ruby", "~> 1.3",  require: false
 
 gemspec path: ".."

gemfiles/gemfile-2-3

@@ -0,0 +1,8 @@
+source "https://rubygems.org"
+
+gem "json",      "~> 2.0",  require: false
+gem "json_pure", "~> 2.0",  require: false
+gem "oj",        "~> 3.0",  require: false
+gem "yajl-ruby", "~> 1.3",  require: false
+
+gemspec path: ".."

lib/multi_json/adapters/oj.rb

@@ -34,10 +34,29 @@ def load(string, options = {})
         ::Oj.load(string, options)
       end
 
-      def dump(object, options = {})
-        options.merge!(:indent => 2) if options[:pretty]
-        options[:indent] = options[:indent].to_i if options[:indent]
-        ::Oj.dump(object, options)
+      case ::Oj::VERSION
+      when /\A2\./
+        def dump(object, options = {})
+          options.merge!(:indent => 2) if options[:pretty]
+          options[:indent] = options[:indent].to_i if options[:indent]
+          ::Oj.dump(object, options)
+        end
+      when /\A3\./
+        PRETTY_STATE_PROTOTYPE = {
+          :indent                => "  ",
+          :space                 => " ",
+          :space_before          => "",
+          :object_nl             => "\n",
+          :array_nl              => "\n",
+          :ascii_only            => false,
+        }
+
+        def dump(object, options = {})
+          options.merge!(PRETTY_STATE_PROTOTYPE.dup) if options.delete(:pretty)
+          ::Oj.dump(object, options)
+        end
+      else
+        fail "Unsupported Oj version: #{::Oj::VERSION}"
       end
     end
   end