Fix validation error message when historical data is empty

ee/app/models/license.rb

@@ -341,6 +341,10 @@ class License < ActiveRecord::Base
     HistoricalData.during(from..to).maximum(:active_user_count) || 0
   end
 
+  def empty_historical_max?
+    historical_max == 0
+  end
+
   def check_users_limit
     return unless restricted_user_count
 
@@ -350,8 +354,9 @@ class License < ActiveRecord::Base
       return if restricted_user_count >= historical_max
     end
 
-    overage = historical_max - restricted_user_count
-    add_limit_error(user_count: historical_max, restricted_user_count: restricted_user_count, overage: overage)
+    user_count = empty_historical_max? ? current_active_users_count : historical_max
+
+    add_limit_error(current_period: empty_historical_max?, user_count: user_count)
   end
 
   def check_trueup
@@ -359,7 +364,6 @@ class License < ActiveRecord::Base
     trueup_from         = Date.parse(restrictions[:trueup_from]) rescue (starts_at - 1.year)
     trueup_to           = Date.parse(restrictions[:trueup_to]) rescue starts_at
     max_historical      = historical_max(trueup_from, trueup_to)
-    overage             = current_active_users_count - restricted_user_count
     expected_trueup_qty = if previous_user_count
                             max_historical - previous_user_count
                           else
@@ -368,7 +372,7 @@ class License < ActiveRecord::Base
 
     if trueup_qty >= expected_trueup_qty
       if restricted_user_count < current_active_users_count
-        add_limit_error(trueup: true, user_count: current_active_users_count, restricted_user_count: restricted_user_count, overage: overage)
+        add_limit_error(user_count: current_active_users_count)
       end
     else
       message = "You have applied a True-up for #{trueup_qty} #{"user".pluralize(trueup_qty)} "
@@ -379,8 +383,10 @@ class License < ActiveRecord::Base
     end
   end
 
-  def add_limit_error(trueup: false, user_count:, restricted_user_count:, overage:)
-    message =  trueup ? "This GitLab installation currently has " : "During the year before this license started, this GitLab installation had "
+  def add_limit_error(current_period: true, user_count:)
+    overage = user_count - restricted_user_count
+
+    message =  current_period ? "This GitLab installation currently has " : "During the year before this license started, this GitLab installation had "
     message << "#{number_with_delimiter(user_count)} active #{"user".pluralize(user_count)}, "
     message << "exceeding this license's limit of #{number_with_delimiter(restricted_user_count)} by "
     message << "#{number_with_delimiter(overage)} #{"user".pluralize(overage)}. "

ee/changelogs/unreleased/5268-fix-wrong-error-message-for-license-key.yml

+---
+title: Fix validation error message when historical data is empty
+merge_request: 4961
+author:
+type: fixed

ee/spec/models/license_spec.rb

@@ -34,6 +34,34 @@ describe License do
         end
       end
 
+      context 'without historical data' do
+        before do
+          create_list(:user, 2)
+
+          gl_license.restrictions = {
+            previous_user_count: 1,
+            active_user_count: User.active.count - 1
+          }
+
+          allow(license).to receive(:historical_max).and_return(0)
+        end
+
+        context 'with previous_user_count and active users above of license limit' do
+          it 'is invalid' do
+            expect(license).to be_invalid
+          end
+
+          it 'shows the proper error message' do
+            license.valid?
+
+            error_msg = "This GitLab installation currently has 2 active users, exceeding this license's limit of 1 by 1 user. "
+            error_msg << "Please upload a license for at least 2 users or contact sales at renewals@gitlab.com"
+
+            expect(license.errors[:base].first).to eq(error_msg)
+          end
+        end
+      end
+
       context "when the active user count restriction is exceeded" do
         before do
           gl_license.restrictions = { active_user_count: active_user_count - 1 }