fix(migrations) stop depending on the order as recorded

Migrations are recorded in the datastore and then the order in which
they appear there is relevant for determining if they should run.

Once something goes out-of-sync on every start/restart it will keep
running migrations over and over again.

From #2869

kong/dao/factory.lua

@@ -251,10 +251,14 @@ end
 
 local function migrate(self, identifier, migrations_modules, cur_migrations, on_migrate, on_success)
   local migrations = migrations_modules[identifier]
-  local recorded = cur_migrations[identifier] or {}
+  local recorded = {}
+  for _, name in ipairs(cur_migrations[identifier] or {}) do
+    recorded[name] = true
+  end
+
   local to_run = {}
-  for i, mig in ipairs(migrations) do
-    if mig.name ~= recorded[i] then
+  for _, mig in ipairs(migrations) do
+    if not recorded[mig.name] then
       to_run[#to_run + 1] = mig
     end
   end

spec/02-integration/03-dao/02-migrations_spec.lua

@@ -98,6 +98,29 @@ helpers.for_each_dao(function(kong_config)
         assert.falsy(err)
         assert.True(ok)
 
+        assert.spy(on_migration).was_not_called()
+        assert.spy(on_success).was_not_called()
+      end)
+      it("should not depend on order of the migration entries", function()
+        local old_fetcher = factory.current_migrations
+        finally(function()
+          factory.current_migrations = old_fetcher
+        end)
+
+        factory.current_migrations = function(...)
+          local mig = old_fetcher(...)
+          local core = mig.core
+          core[#core], core[#core-1] = core[#core-1], core[#core]
+          return mig
+        end
+
+        local on_migration = spy.new(function() end)
+        local on_success = spy.new(function() end)
+
+        local ok, err = factory:run_migrations(on_migration, on_success)
+        assert.falsy(err)
+        assert.True(ok)
+
         assert.spy(on_migration).was_not_called()
         assert.spy(on_success).was_not_called()
       end)