Handle links to course home in course copy

fixes LS-2325
flag=none

test plan:
- Create a page
- In the content of the page create a link to the course home by clicking
 the dropdown next to the link button in the RCE menu, then clicking
 Course Links, expand Course Navigation, then select Home
- With the Home link in the content, save the page
- Export the course
- Import the course content into a new course
- Verify the link in the imported page content is linked to the new page's
 home navigation and not the old course
- Also verify just using the Copy Course from Import Course Content also
 changes the home navigiation link as expected

Change-Id: Ib7779a4c42f9669ac4da6408a2fbd453ae31a039
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/267975
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jackson Howe <jackson.howe@instructure.com>
QA-Review: Jackson Howe <jackson.howe@instructure.com>
Product-Review: Eric Saupe <eric.saupe@instructure.com>

lib/cc/cc_helper.rb

@@ -223,6 +223,11 @@ module CCHelper
           match.url.sub(/course( |%20)files/, WEB_CONTENT_TOKEN)
         end
       end
+      @rewriter.set_handler('courses') do |match|
+        if match.obj_id == @course.id
+          "#{COURSE_TOKEN}/"
+        end
+      end
       @rewriter.set_handler('files') do |match|
         if match.obj_id.nil?
           if match_data = match.url.match(%r{/files/folder/(.*)})

lib/user_content.rb

@@ -72,7 +72,7 @@ module UserContent
       if !use_updated_math_rendering
         mathml = UserContent.latex_to_mathml(equation)
         next if mathml.blank?
-        
+
         mathml_span = node.fragment(
           "<span class=\"hidden-readable\">#{mathml}</span>"
         ).children.first
@@ -150,6 +150,7 @@ module UserContent
       'assignments' => :Assignment,
       'announcements' => :Announcement,
       'calendar_events' => :CalendarEvent,
+      'courses' => :Course,
       'discussion_topics' => :DiscussionTopic,
       'collaborations' => :Collaboration,
       'files' => :Attachment,
@@ -213,7 +214,7 @@ module UserContent
 
       html.gsub(@toplevel_regex) do |url|
         _absolute_part, prefix, type, obj_id, rest = [$1, $2, $3, $4, $5]
-        next url if !@contextless_types.include?(type) && prefix != @context_prefix
+        next url if !@contextless_types.include?(type) && prefix != @context_prefix && url != @context_prefix
 
         if type != "wiki" && type != "pages"
           if obj_id.to_i > 0

spec/lib/cc/cc_helper_spec.rb

@@ -197,6 +197,13 @@ describe CC::CCHelper do
       expect(translated).to match %r{\$CANVAS_COURSE_REFERENCE\$/files}
     end
 
+    it "should interpret links to the home page as normal course pages" do
+      @exporter = CC::CCHelper::HtmlContentExporter.new(@course, @user, :for_course_copy => true)
+      html = %{<a href="/courses/#{@course.id}">Home page index</a>}
+      translated = @exporter.html_content(html)
+      expect(translated).to match %r{\$CANVAS_COURSE_REFERENCE\$/}
+    end
+
     it "should prepend the domain to links outside the course" do
       allow(HostUrl).to receive(:protocol).and_return('http')
       allow(HostUrl).to receive(:context_host).and_return('www.example.com:8080')