render correct page after joining self-signup group

fixes #10880

when joining a self-signup group, permissions were being incorrectly cached
causing a 'membership pending' page to be shown.

test plan:
- as a teacher, create a set of course groups, and allow self-signup
- as a student, join one of these groups
- it should not say 'membership pending'
- it should say 'you joined the group'

Change-Id: Ic11cdeead8db23293e64faa0dc3c803310e426cc
Reviewed-on: https://gerrit.instructure.com/13959
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>

Author: simonista

app/models/group.rb

@@ -220,6 +220,8 @@ def add_user(user, new_record_state=nil, moderator=nil)
     else
       member = self.group_memberships.create(attrs)
     end
+    # permissions for this user in the group are probably different now
+    Rails.cache.delete(permission_cache_key_for(user))
     return member
   end
 

spec/integration/groups_spec.rb

@@ -30,4 +30,17 @@
     html = Nokogiri::HTML(response.body)
     html.css('.floating_links a.add').attribute("href").text.should == "/groups/#{@group.id}/announcements#new"
   end
+
+  it "should not rendering 'pending' page when joining a self-signup group" do
+    enable_cache do
+      course_with_student_logged_in(:active_all => true)
+      category1 = @course.group_categories.create!(:name => "category 1")
+      category1.configure_self_signup(true, false)
+      category1.save!
+      g1 = @course.groups.create!(:name => "some group", :group_category => category1)
+
+      get "/courses/#{@course.id}/groups/#{g1.id}?join=1"
+      response.body.should_not =~ /This group has received your request to join/
+    end
+  end
 end

vendor/plugins/adheres_to_policy/lib/adheres_to_policy.rb

@@ -124,7 +124,7 @@ def grants_rights?(user, *sought_rights)
         # once
         granted_rights = if cache_lookup
           # Check and cache all the things!
-          Rails.cache.fetch(['context_permissions', self, user].cache_key, :expires_in => 1.hour) do
+          Rails.cache.fetch(permission_cache_key_for(user), :expires_in => 1.hour) do
             check_policy(user)
           end
         else
@@ -149,6 +149,10 @@ def has_rights?(obj, *sought_rights)
         obj.grants_rights?(self, *sought_rights)
       end
 
+      def permission_cache_key_for(user)
+        ['context_permissions', self, user].cache_key
+      end
+
     end # InstanceMethods
   end # AdheresToPolicy
 end # Instructure