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]

db/migrate/20160705054938_add_protected_branches_push_access.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddProtectedBranchesPushAccess < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  def change
+    create_table :protected_branch_push_access_levels do |t|
+      t.references :protected_branch, index: { name: "index_protected_branch_push_access" }, foreign_key: true, null: false
+      t.integer :access_level, default: 0, null: false
+
+      t.timestamps null: false
+    end
+  end
+end

db/migrate/20160705054952_add_protected_branches_merge_access.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddProtectedBranchesMergeAccess < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  def change
+    create_table :protected_branch_merge_access_levels do |t|
+      t.references :protected_branch, index: { name: "index_protected_branch_merge_access" }, foreign_key: true, null: false
+      t.integer :access_level, default: 0, null: false
+
+      t.timestamps null: false
+    end
+  end
+end

db/migrate/20160705055254_move_from_developers_can_merge_to_protected_branches_merge_access.rb

+# 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

db/migrate/20160705055308_move_from_developers_can_push_to_protected_branches_push_access.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class MoveFromDevelopersCanPushToProtectedBranchesPushAccess < 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_push_access_levels (protected_branch_id, access_level, created_at, updated_at)
+        SELECT id, (CASE WHEN developers_can_push THEN 1 ELSE 0 END), now(), now()
+          FROM protected_branches
+    HEREDOC
+  end
+
+  def down
+    execute <<-HEREDOC
+      UPDATE protected_branches SET developers_can_push = TRUE
+        WHERE id IN (SELECT protected_branch_id FROM protected_branch_push_access_levels
+                       WHERE access_level = 1);
+    HEREDOC
+  end
+end

db/migrate/20160705055809_remove_developers_can_push_from_protected_branches.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RemoveDevelopersCanPushFromProtectedBranches < 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 change
+    remove_column :protected_branches, :developers_can_push, :boolean
+  end
+end

db/migrate/20160705055813_remove_developers_can_merge_from_protected_branches.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RemoveDevelopersCanMergeFromProtectedBranches < 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 change
+    remove_column :protected_branches, :developers_can_merge, :boolean
+  end
+end

db/schema.rb

@@ -867,13 +867,29 @@ ActiveRecord::Schema.define(version: 20160722221922) do
   add_index "projects", ["star_count"], name: "index_projects_on_star_count", using: :btree
   add_index "projects", ["visibility_level"], name: "index_projects_on_visibility_level", using: :btree
 
+  create_table "protected_branch_merge_access_levels", force: :cascade do |t|
+    t.integer  "protected_branch_id",             null: false
+    t.integer  "access_level",        default: 0, null: false
+    t.datetime "created_at",                      null: false
+    t.datetime "updated_at",                      null: false
+  end
+
+  add_index "protected_branch_merge_access_levels", ["protected_branch_id"], name: "index_protected_branch_merge_access", using: :btree
+
+  create_table "protected_branch_push_access_levels", force: :cascade do |t|
+    t.integer  "protected_branch_id",             null: false
+    t.integer  "access_level",        default: 0, null: false
+    t.datetime "created_at",                      null: false
+    t.datetime "updated_at",                      null: false
+  end
+
+  add_index "protected_branch_push_access_levels", ["protected_branch_id"], name: "index_protected_branch_push_access", using: :btree
+
   create_table "protected_branches", force: :cascade do |t|
     t.integer  "project_id", null: false
     t.string   "name",       null: false
     t.datetime "created_at"
     t.datetime "updated_at"
-    t.boolean  "developers_can_push",  default: false, null: false
-    t.boolean  "developers_can_merge", default: false, null: false
   end
 
   add_index "protected_branches", ["project_id"], name: "index_protected_branches_on_project_id", using: :btree
@@ -1136,5 +1152,7 @@ ActiveRecord::Schema.define(version: 20160722221922) do
   add_index "web_hooks", ["project_id"], name: "index_web_hooks_on_project_id", using: :btree
 
   add_foreign_key "personal_access_tokens", "users"
+  add_foreign_key "protected_branch_merge_access_levels", "protected_branches"
+  add_foreign_key "protected_branch_push_access_levels", "protected_branches"
   add_foreign_key "u2f_registrations", "users"
 end