Add strip_index filter (#6075)

Merge pull request 6075

lib/jekyll/filters/url_filters.rb

@@ -28,6 +28,16 @@ module Jekyll
         ).normalize.to_s
       end
 
+      # Strips trailing `/index.html` from URLs to create pretty permalinks
+      #
+      # input - the URL with a possible `/index.html`
+      #
+      # Returns a URL with the trailing `/index.html` removed
+      def strip_index(input)
+        return if input.nil? || input.to_s.empty?
+        input.sub(%r!/index\.html?$!, "/")
+      end
+
       private
 
       def site

test/test_filters.rb

@@ -493,6 +493,28 @@ class TestFilters < JekyllUnitTest
       end
     end
 
+    context "strip_index filter" do
+      should "strip trailing /index.html" do
+        assert_equal "/foo/", @filter.strip_index("/foo/index.html")
+      end
+
+      should "strip trailing /index.htm" do
+        assert_equal "/foo/", @filter.strip_index("/foo/index.htm")
+      end
+
+      should "not strip HTML in the middle of URLs" do
+        assert_equal "/index.html/foo", @filter.strip_index("/index.html/foo")
+      end
+
+      should "not raise an error on nil strings" do
+        assert_nil @filter.strip_index(nil)
+      end
+
+      should "not mangle other URLs" do
+        assert_equal "/foo/", @filter.strip_index("/foo/")
+      end
+    end
+
     context "jsonify filter" do
       should "convert hash to json" do
         assert_equal "{\"age\":18}", @filter.jsonify({ :age => 18 })
@@ -742,7 +764,7 @@ class TestFilters < JekyllUnitTest
         assert_equal 4.7, results[0]["rating"]
       end
 
-      should "always return an array if the object responds to `select`" do
+      should "always return an array if the object responds to 'select'" do
         results = @filter.where(SelectDummy.new, "obj", "1 == 1")
         assert_equal [], results
       end
@@ -819,7 +841,7 @@ class TestFilters < JekyllUnitTest
         assert_equal site.posts.find { |p| p.title == "Foo Bar" }, results.first
       end
 
-      should "always return an array if the object responds to `select`" do
+      should "always return an array if the object responds to 'select'" do
         results = @filter.where_exp(SelectDummy.new, "obj", "1 == 1")
         assert_equal [], results
       end