add 'default_enabled' to feature flags

This allows you to default a feature flag to 'on' when
checking whether it's enabled/disabled.

doc/development/feature_flags.md

@@ -58,13 +58,20 @@ Features that are developed and are intended to be merged behind a feature flag
 should not include a changelog entry. The entry should be added in the merge
 request removing the feature flags.
 
+In the rare case that you need the feature flag to be on automatically, use
+`default_enabled: true` when checking:
+
+```ruby
+Feature.enabled?(:feature_flag, project, default_enabled: true)
+```
+
 ### Specs
 
 In the test environment `Feature.enabled?` is stubbed to always respond to `true`,
 so we make sure behavior under feature flag doesn't go untested in some non-specific
 contexts.
- 
-If you need to test the feature flag in a different state, you need to stub it with: 
+
+If you need to test the feature flag in a different state, you need to stub it with:
 
 ```ruby
 stub_feature_flags(my_feature_flag: false)

lib/feature.rb

@@ -42,13 +42,17 @@ class Feature
       persisted_names.include?(feature.name.to_s)
     end
 
-    def enabled?(key, thing = nil)
-      get(key).enabled?(thing)
+    def enabled?(key, thing = nil, default_enabled: false)
+      feature = Feature.get(key)
+      return feature.enabled?(thing) unless default_enabled
+
+      # If the feature has been set, always evaluate
+      Feature.persisted?(feature) ? feature.enabled?(thing) : true
     end
 
-    def disabled?(key, thing = nil)
+    def disabled?(key, thing = nil, default_enabled: false)
       # we need to make different method calls to make it easy to mock / define expectations in test mode
-      thing.nil? ? !enabled?(key) : !enabled?(key, thing)
+      thing.nil? ? !enabled?(key, default_enabled: default_enabled) : !enabled?(key, thing, default_enabled: default_enabled)
     end
 
     def enable(key, thing = true)

spec/lib/feature_spec.rb

@@ -119,6 +119,10 @@ describe Feature do
       expect(described_class.enabled?(:some_random_feature_flag)).to be_falsey
     end
 
+    it 'returns true for undefined feature with default_enabled' do
+      expect(described_class.enabled?(:some_random_feature_flag, default_enabled: true)).to be_truthy
+    end
+
     it 'returns false for existing disabled feature in the database' do
       described_class.disable(:disabled_feature_flag)
 
@@ -160,6 +164,10 @@ describe Feature do
       expect(described_class.disabled?(:some_random_feature_flag)).to be_truthy
     end
 
+    it 'returns false for undefined feature with default_enabled' do
+      expect(described_class.disabled?(:some_random_feature_flag, default_enabled: true)).to be_falsey
+    end
+
     it 'returns true for existing disabled feature in the database' do
       described_class.disable(:disabled_feature_flag)
 

spec/support/helpers/stub_feature_flags.rb

@@ -4,8 +4,8 @@ module StubFeatureFlags
   # @param [Hash] features where key is feature name and value is boolean whether enabled or not
   def stub_feature_flags(features)
     features.each do |feature_name, enabled|
-      allow(Feature).to receive(:enabled?).with(feature_name) { enabled }
-      allow(Feature).to receive(:enabled?).with(feature_name.to_s) { enabled }
+      allow(Feature).to receive(:enabled?).with(feature_name, any_args) { enabled }
+      allow(Feature).to receive(:enabled?).with(feature_name.to_s, any_args) { enabled }
     end
   end
 end