add file name in blank anchor tags in imported cc content

test plan:
* import a cc package with blank file anchor tags in
 html content
* they should be visible because they are now populated
 with the file name

closes #LA-1020

Change-Id: I82adb68a01b134ecf29ee4db6dde11487b8b186c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/237443
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Jeremy Stanley <jeremy@instructure.com>
Product-Review: James Williams <jamesw@instructure.com>

lib/cc/importer/standard/converter.rb

@@ -94,6 +94,7 @@ module CC::Importer::Standard
     end
 
     def find_file_migration_id(path)
+      return unless path.present?
       mig_id = @file_path_migration_id[path] || @file_path_migration_id[path.gsub(%r{\$[^$]*\$|\.\./}, '')] ||
         @file_path_migration_id[path.gsub(%r{\$[^$]*\$|\.\./}, '').sub(WEB_RESOURCES_FOLDER + '/', '')]
 
@@ -167,6 +168,10 @@ module CC::Importer::Standard
                 val.gsub!(FILEBASE_REGEX, '')
                 if new_url = get_canvas_att_replacement_url(val, resource_dir)
                   node[attr] = URI::escape(new_url)
+
+                  if node.text.strip.blank? && !node.at_css("img") # add in the filename if the link is blank and doesn't have something visible like an image
+                    node.inner_html = HtmlTextHelper.escape_html(File.basename(val)) + (node.inner_html || "")
+                  end
                 end
               else
                 if ImportedHtmlConverter.relative_url?(val)

spec/lib/cc/importer/common_cartridge_converter_spec.rb

@@ -717,4 +717,16 @@ describe "other cc files" do
       expect(@course.reload.syllabus_body).to include("<p>beep beep</p>")
     end
   end
+
+  describe "empty file link name inference" do
+    it "should add the file name to empty links in html content" do
+      import_cc_file("cc_empty_link.zip")
+      assmt = @course.assignments.where(:migration_id => "assignment1").first
+      file = @course.attachments.where(:migration_id => "file1").first
+      doc = Nokogiri::HTML::DocumentFragment.parse(assmt.description)
+      link = doc.at_css("a")
+      expect(link.attr('href')).to include("courses/#{@course.id}/files/#{file.id}")
+      expect(link.text.strip).to eq file.display_name
+    end
+  end
 end