Add ruby filter

lib/fast_haml/filter_compilers.rb

@@ -34,3 +34,4 @@ def self.find(name)
 require 'fast_haml/filter_compilers/javascript'
 require 'fast_haml/filter_compilers/plain'
 require 'fast_haml/filter_compilers/preserve'
+require 'fast_haml/filter_compilers/ruby'

lib/fast_haml/filter_compilers/ruby.rb

@@ -0,0 +1,13 @@
+require 'fast_haml/filter_compilers/base'
+
+module FastHaml
+  module FilterCompilers
+    class Ruby < Base
+      def compile(texts)
+        [:multi, [:code, texts.join("\n")], [:newline]]
+      end
+    end
+
+    register(:ruby, Ruby)
+  end
+end

spec/render/filters/ruby_spec.rb

@@ -0,0 +1,13 @@
+require 'spec_helper'
+
+RSpec.describe 'Ruby filter rendering', type: :render do
+  it 'renders ruby filter' do
+    expect(render_string(<<HAML)).to eq("\n3\n")
+:ruby
+  hash = {
+    a: 3,
+  }
+= hash[:a]
+HAML
+  end
+end