post_url tag raises ArgumentError for invalid name

Using post_url tag with invalid name raises TypeError.

It should raise ArgumentError and should display detail of the error to
fix the error.

lib/jekyll/tags/post_url.rb

@@ -7,6 +7,7 @@ module Jekyll
 
       def initialize(name)
         all, path, date, slug = *name.sub(/^\//, "").match(MATCHER)
+        raise ArgumentError unless all
         @slug = path ? path + slug : slug
         @date = Time.parse(date)
       end
@@ -38,7 +39,15 @@ module Jekyll
       def initialize(tag_name, post, tokens)
         super
         @orig_post = post.strip
+        begin
           @post = PostComparer.new(@orig_post)
+        rescue
+          raise ArgumentError.new <<-eos
+Could not parse name of post "#{@orig_post}" in tag 'post_url'.
+
+Make sure the post exists and the name is correct.
+eos
+        end
       end
 
       def render(context)

test/test_tags.rb

@@ -237,6 +237,22 @@ CONTENT
     end
   end
 
+  context "simple page with invalid post name linking" do
+    should "cause an error" do
+      content = <<CONTENT
+---
+title: Invalid post name linking
+---
+
+{% post_url abc2008-11-21-complex %}
+CONTENT
+
+      assert_raise ArgumentError do
+        create_post(content, {'permalink' => 'pretty', 'source' => source_dir, 'destination' => dest_dir, 'read_posts' => true})
+      end
+    end
+  end
+
   context "gist tag" do
     context "simple" do
       setup do