If migrations are pending, make CurrentSettings use existing values and populate missing columns with defaultssh-refactor-current-settings

master was failing because `ApplicationSetting.create_from_defaults` attempted
to write to a column that did not exist in the database. This occurred in a
`rake db:migrate` task, which was unable to perform the migration that would
have added the missing column in the first place.

In 9.3 RC2, we also had a bug where password sign-ins were disabled because
there were many pending migrations. The problem occurred because
`fake_application_settings` was being returned with an OpenStruct that did not
include the predicate method `signup_enabled?`. As a result, the value would
erroneously return `nil` instead of `true`. This commit uses the values of the
defaults to mimic this behavior.

This commit also refactors some of the logic to be clearer.

1 files changed, 27 insertions, 0 deletions

diff --git a/lib/gitlab/fake_application_settings.rb b/lib/gitlab/fake_application_settings.rb
new file mode 100644
index 00000000000..bb14a8cd9e7
--- /dev/null
+++ b/lib/gitlab/fake_application_settings.rb
@@ -0,0 +1,27 @@
+# This class extends an OpenStruct object by adding predicate methods to mimic
+# ActiveRecord access. We rely on the initial values being true or false to
+# determine whether to define a predicate method because for a newly-added
+# column that has not been migrated yet, there is no way to determine the
+# column type without parsing db/schema.rb.
+module Gitlab
+  class FakeApplicationSettings < OpenStruct
+    def initialize(options = {})
+      super
+
+      FakeApplicationSettings.define_predicate_methods(options)
+    end
+
+    # Mimic ActiveRecord predicate methods for boolean values
+    def self.define_predicate_methods(options)
+      options.each do |key, value|
+        next if key.to_s.end_with?('?')
+        next unless [true, false].include?(value)
+
+        define_method "#{key}?" do
+          actual_key = key.to_s.chomp('?')
+          self[actual_key]
+        end
+      end
+    end
+  end
+end