check if relative URL contains a colon

fixes #2834

lib/jekyll/errors.rb

@@ -9,8 +9,9 @@ module Jekyll
     InvalidYAMLFrontMatterError = Class.new(FatalException)
     MissingDependencyException  = Class.new(FatalException)
 
-    InvalidDateError = Class.new(FatalException)
-    InvalidPostNameError = Class.new(FatalException)
-    PostURLError = Class.new(FatalException)
+    InvalidDateError      = Class.new(FatalException)
+    InvalidPostNameError  = Class.new(FatalException)
+    PostURLError          = Class.new(FatalException)
+    InvalidURLError       = Class.new(FatalException)
   end
 end

lib/jekyll/url.rb

@@ -35,8 +35,15 @@ module Jekyll
     # The generated relative URL of the resource
     #
     # Returns the String URL
+    # Raises a Jekyll::Errors::InvalidURLError if the relative URL contains a colon
     def to_s
-      sanitize_url(generated_permalink || generated_url)
+      sanitized_url = sanitize_url(generated_permalink || generated_url)
+      if sanitized_url.include?(":")
+        raise Jekyll::Errors::InvalidURLError,
+          "The URL #{sanitized_url} is invalid because it contains a colon."
+      else
+        sanitized_url
+      end
     end
 
     # Generates a URL from the permalink

test/test_url.rb

@@ -70,5 +70,15 @@ class TestURL < JekyllUnitTest
         :placeholders => matching_doc.url_placeholders
       ).to_s
     end
+
+    should "throw an exception if the URL contains a colon" do
+      url = URL.new(
+        :template     => "/:x/:y/:z",
+        :placeholders => { :x => "foo", :z => "bar" }
+      )
+      assert_raises Jekyll::Errors::InvalidURLError do
+        url.to_s
+      end
+    end
   end
 end