Add a new filter to_uri.

app/concerns/liquid_droppable.rb

@@ -27,4 +27,20 @@ module LiquidDroppable
   def to_liquid
     self.class::Drop.new(self)
   end
+
+  require 'uri'
+
+  class URIDrop < Drop
+    URI::Generic::COMPONENT.each { |attr|
+      define_method(attr) {
+        @object.__send__(attr)
+      }
+    }
+  end
+
+  class ::URI::Generic
+    def to_liquid
+      URIDrop.new(self)
+    end
+  end
 end

app/concerns/liquid_interpolatable.rb

@@ -116,6 +116,22 @@ module LiquidInterpolatable
       CGI.escape(string) rescue string
     end
 
+    # Parse an input into a URI object, optionally resolving it
+    # against a base URI if given.
+    #
+    # A URI object will have the following properties: scheme,
+    # userinfo, host, port, registry, path, opaque, query, and
+    # fragment.
+    def to_uri(uri, base_uri = nil)
+      if base_uri
+        URI(base_uri) + uri.to_s
+      else
+        URI(uri.to_s)
+      end
+    rescue URI::Error
+      nil
+    end
+
     # Escape a string for use in XPath expression
     def to_xpath(string)
       subs = string.to_s.scan(/\G(?:\A\z|[^"]+|[^']+)/).map { |x|

spec/concerns/liquid_interpolatable_spec.rb

@@ -59,4 +59,41 @@ describe LiquidInterpolatable::Filters do
       @filter.to_xpath_roundtrip(1).should == '1'
     end
   end
+
+  describe 'to_uri' do
+    before do
+      @agent = Agents::InterpolatableAgent.new(name: "test", options: { 'foo' => '{% assign u = s | to_uri %}{{ u.path }}' })
+      @agent.interpolation_context['s'] = 'http://example.com/dir/1?q=test'
+    end
+
+    it 'should parse an abosule URI' do
+      @filter.to_uri('http://example.net/index.html', 'http://example.com/dir/1').should == URI('http://example.net/index.html')
+    end
+
+    it 'should parse an abosule URI with a base URI specified' do
+      @filter.to_uri('http://example.net/index.html', 'http://example.com/dir/1').should == URI('http://example.net/index.html')
+    end
+
+    it 'should parse a relative URI with a base URI specified' do
+      @filter.to_uri('foo/index.html', 'http://example.com/dir/1').should == URI('http://example.com/dir/foo/index.html')
+    end
+
+    it 'should parse an abosule URI with a base URI specified' do
+      @filter.to_uri('http://example.net/index.html', 'http://example.com/dir/1').should == URI('http://example.net/index.html')
+    end
+
+    it 'should stringify a non-string operand' do
+      @filter.to_uri(123, 'http://example.com/dir/1').should == URI('http://example.com/dir/123')
+    end
+
+    it 'should return a URI value in interpolation' do
+      @agent.interpolated['foo'].should == '/dir/1'
+    end
+
+    it 'should return a URI value resolved against a base URI in interpolation' do
+      @agent.options['foo'] = '{% assign u = s | to_uri:"http://example.com/dir/1" %}{{ u.path }}'
+      @agent.interpolation_context['s'] = 'foo/index.html'
+      @agent.interpolated['foo'].should == '/dir/foo/index.html'
+    end
+  end
 end