Merge branch 'fix_migration_that_adds_ff_merge_field' into 'master'

Fix a migration that adds merge_requests_ff_only_enabled column to MR table

Closes #39382 and #39357

See merge request gitlab-org/gitlab-ce!15195

changelogs/unreleased/fix_migration_that_adds_ff_merge_field.yml

+---
+title: Fix a migration that adds merge_requests_ff_only_enabled column to MR table
+merge_request:
+author:
+type: fixed

db/migrate/20150827121444_add_fast_forward_option_to_project.rb

@@ -8,7 +8,11 @@ class AddFastForwardOptionToProject < ActiveRecord::Migration
   disable_ddl_transaction!
 
   def up
-    add_column_with_default(:projects, :merge_requests_ff_only_enabled, :boolean, default: false)
+    # We put condition here because of a mistake we made a couple of years ago
+    # see https://gitlab.com/gitlab-org/gitlab-ce/issues/39382#note_45716103
+    unless column_exists?(:projects, :merge_requests_ff_only_enabled)
+      add_column_with_default(:projects, :merge_requests_ff_only_enabled, :boolean, default: false)
+    end
   end
 
   def down