Fix upcoming milestone for far-future due dates

`NOW()` is a timestamp, with a maximum year (in Postgres) 294276 AD.

`milestones.due_date` is a date with a maximum year (again, in Postgres)
of 5874897 AD.

If there is a due date past the limit for the timestamp, comparing the
two will fail with:
    ERROR:  date out of range for timestamp

We also need to add validations to keep the due dates sensible, but for
now we can simply use `CURRENT_DATE` instead of `NOW()`, so the types
match with no coercion needed.

app/models/milestone.rb

@@ -149,7 +149,7 @@ class Milestone < ActiveRecord::Base
   def self.upcoming_ids(projects, groups)
     rel = unscoped
             .for_projects_and_groups(projects, groups)
-            .active.where('milestones.due_date > NOW()')
+            .active.where('milestones.due_date > CURRENT_DATE')
 
     if Gitlab::Database.postgresql?
       rel.order(:project_id, :group_id, :due_date).select('DISTINCT ON (project_id, group_id) id')
@@ -161,7 +161,7 @@ class Milestone < ActiveRecord::Base
           ON milestones.project_id <=> earlier_milestones.project_id
             AND milestones.group_id <=> earlier_milestones.group_id
             AND milestones.due_date > earlier_milestones.due_date
-            AND earlier_milestones.due_date > NOW()
+            AND earlier_milestones.due_date > CURRENT_DATE
             AND earlier_milestones.state = 'active'
       HEREDOC
 

changelogs/unreleased/use-date-for-upcoming-milestone-comparison.yml

+---
+title: Fix upcoming milestone when there are milestones with far-future due dates
+merge_request:
+author:
+type: fixed