clear special account cache after editing

should fix problems with account settings and help links
 on local/single-account environments

test plan:
* should be able to edit help links and show changes
 right away for the default account

closes #CNVS-31213 #CNVS-31218

Change-Id: Ifc6a2b208f0a0dae99579a0a0e229ed1307ed63c
Reviewed-on: https://gerrit.instructure.com/88635
Tested-by: Jenkins
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Heath Hales <hhales@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>

Author: maneframe

app/models/account.rb

@@ -109,6 +109,7 @@ def inherited_assessment_question_banks(include_self = false, *additional_contex
 
   before_save :setup_cache_invalidation
   after_save :invalidate_caches_if_changed
+  after_update :clear_special_account_cache_if_special
 
   after_create :default_enrollment_term
   after_create :enable_canvas_authentication
@@ -1162,6 +1163,12 @@ def all_special_accounts
   define_special_account(:default, 'Default Account') # Account.default
   define_special_account(:site_admin) # Account.site_admin
 
+  def clear_special_account_cache_if_special
+    if self.shard == Shard.birth && Account.special_account_ids.values.map(&:to_i).include?(self.id)
+      Account.clear_special_account_cache!(true)
+    end
+  end
+
   # an opportunity for plugins to load some other stuff up before caching the account
   def precache
   end

spec/models/account_spec.rb

@@ -1540,4 +1540,14 @@ def account_with_admin_and_restricted_user(account, restricted_role)
       end
     end
   end
+
+  it "should clear special account cache on updates to special accounts" do
+    expect(Account.default.settings[:blah]).to be_nil
+
+    non_cached = Account.find(Account.default.id)
+    non_cached.settings[:blah] = true
+    non_cached.save!
+
+    expect(Account.default.settings[:blah]).to eq true
+  end
 end