fix date parsing in file names to be stricter

lib/jekyll/document.rb

@@ -9,7 +9,7 @@ class Document
 
     YAML_FRONT_MATTER_REGEXP = %r!\A(---\s*\n.*?\n?)^((---|\.\.\.)\s*$\n?)!m
     DATELESS_FILENAME_MATCHER = %r!^(?:.+/)*(.*)(\.[^.]+)$!
-    DATE_FILENAME_MATCHER = %r!^(?:.+/)*(\d+-\d+-\d+)-(.*)(\.[^.]+)$!
+    DATE_FILENAME_MATCHER = %r!^(?:.+/)*(\d{4}-\d{2}-\d{2})-(.*)(\.[^.]+)$!
 
     # Create a new Document.
     #

test/source/_methods/3940394-21-9393050-fifif1323-test.md

@@ -0,0 +1,5 @@
+---
+title: "this is a test!"
+---
+
+wheee

test/test_document.rb

@@ -492,4 +492,33 @@ def assert_equal_value(key, one, other)
       assert_equal true, File.file?(@dest_file)
     end
   end
+
+  context "a document in a collection with dash-separated numeric file name" do
+    setup do
+      @site = fixture_site({
+        "collections" => {
+          "methods" => {
+            "output" => true
+          }
+        }
+      })
+      @site.process
+      @document = @site.collections["methods"].docs.find do |doc|
+        doc.relative_path == "_methods/3940394-21-9393050-fifif1323-test.md"
+      end
+      @dest_file = dest_dir("methods/3940394-21-9393050-fifif1323-test.html")
+    end
+
+    should "produce the right URL" do
+      assert_equal "/methods/3940394-21-9393050-fifif1323-test.html", @document.url
+    end
+
+    should "produce the right destination" do
+      assert_equal @dest_file, @document.destination(dest_dir)
+    end
+
+    should "be output in the correct place" do
+      assert_equal true, File.file?(@dest_file)
+    end
+  end
 end