Add a series of migrations changing the model-level design of protected branch access levels.

1. Remove the `developers_can_push` and `developers_can_merge` boolean
   columns.

2. Add two new tables, `protected_branches_push_access`, and
   `protected_branches_merge_access`. Each row of these 'access' tables is
   linked to a protected branch, and uses a `access_level` column to
   figure out settings for the protected branch.

3. The `access_level` column is intended to be used with rails' `enum`,
   with `:masters` at index 0 and `:developers` at index 1.

4. Doing it this way has a few advantages:

   - Cleaner path to planned EE features where a protected branch is
     accessible only by certain users or groups.

   - Rails' `enum` doesn't allow a declaration like this due to the
     duplicates. This approach doesn't have this problem.

       enum can_be_pushed_by: [:masters, :developers]
       enum can_be_merged_by: [:masters, :developers]

1 files changed, 33 insertions, 0 deletions

diff --git a/db/migrate/20160705055254_move_from_developers_can_merge_to_protected_branches_merge_access.rb b/db/migrate/20160705055254_move_from_developers_can_merge_to_protected_branches_merge_access.rb
new file mode 100644
index 00000000000..20ca9c3a488
--- /dev/null
+++ b/db/migrate/20160705055254_move_from_developers_can_merge_to_protected_branches_merge_access.rb
@@ -0,0 +1,33 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class MoveFromDevelopersCanMergeToProtectedBranchesMergeAccess < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # When using the methods "add_concurrent_index" or "add_column_with_default"
+  # you must disable the use of transactions as these methods can not run in an
+  # existing transaction. When using "add_concurrent_index" make sure that this
+  # method is the _only_ method called in the migration, any other changes
+  # should go in a separate migration. This ensures that upon failure _only_ the
+  # index creation fails and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  # disable_ddl_transaction!
+
+  def up
+    execute <<-HEREDOC
+      INSERT into protected_branch_merge_access_levels (protected_branch_id, access_level, created_at, updated_at)
+        SELECT id, (CASE WHEN developers_can_merge THEN 1 ELSE 0 END), now(), now()
+          FROM protected_branches
+    HEREDOC
+  end
+
+  def down
+    execute <<-HEREDOC
+      UPDATE protected_branches SET developers_can_merge = TRUE
+        WHERE id IN (SELECT protected_branch_id FROM protected_branch_merge_access_levels
+                       WHERE access_level = 1);
+    HEREDOC
+  end
+end