Keep explicit unlocks' dates when unlock conditions change

app/models/exercise_group.rb

@@ -90,8 +90,11 @@ def exercises_by_unlock_spec
   def group_unlock_conditions=(unlock_conditions)
     group_exercises = exercises(false)
     # Rows granted under other conditions keep their date: fast refresh never revokes them, so moving it would open them early.
+    # Explicit unlocks keep theirs too: the row already started the deadline timer, so a later date would lock it while the timer runs.
     conditions = UnlockSpec.non_date_conditions(unlock_conditions).sort
-    rows_to_move = group_exercises.select { |e| UnlockSpec.non_date_conditions(e.unlock_spec).sort == conditions }.map(&:name)
+    rows_to_move = group_exercises.select do |e|
+      !e.requires_explicit_unlock? && UnlockSpec.non_date_conditions(e.unlock_spec).sort == conditions
+    end.map(&:name)
     group_exercises.each do |e|
       e.unlock_spec = unlock_conditions
       e.save!

spec/models/exercise_group_spec.rb

@@ -61,6 +61,13 @@
       expect(Unlock.where(exercise_name: %w[week1-01 week1-02]).pluck(:valid_after)).to all(eq(Time.zone.parse('2012-05-05')))
     end
 
+    it 'keeps the date of explicit unlocks, whose deadline timer has already started' do
+      [ex1, ex2].each { |ex| ex.update!(deadline_spec: ['unlock + 7 days'].to_json) }
+      group.group_unlock_conditions = ['5.5.2012'].to_json
+
+      expect(Unlock.where(exercise_name: %w[week1-01 week1-02]).pluck(:valid_after)).to all(eq(Time.zone.parse('2011-01-01')))
+    end
+
     it 'leaves unlock rows alone when the conditions are cleared' do
       group.group_unlock_conditions = [].to_json