Feature Flags

Feature Flags

Feature flags gate experimental functionality behind user-configurable settings, enabling safe rollout (default off), user opt-in, and easy rollback.

Checking Feature State

import "github.com/marcus/sidecar/internal/features"

if features.IsEnabled("tmux_interactive_input") {
    // Feature-gated code
}

Adding a New Feature Flag

1. Define the feature in internal/features/features.go:

var MyNewFeature = Feature{
    Name:        "my_new_feature",
    Default:     false,
    Description: "Description of what this enables",
}

2. Add to the allFeatures slice:

var allFeatures = []Feature{
    TmuxInteractiveInput,
    MyNewFeature, // Add here
}

3. Use the feature check in your code:

if features.IsEnabled("my_new_feature") {
    // New functionality
}

User Configuration

Config file (~/.config/sidecar/config.json)

{
  "features": {
    "flags": {
      "tmux_interactive_input": true
    }
  }
}

CLI override (takes precedence over config)

sidecar --enable-feature=tmux_interactive_input
sidecar --disable-feature=tmux_interactive_input
sidecar --enable-feature=feature1,feature2   # Multiple features

Unknown feature names in CLI flags produce a warning but do not prevent startup.

Priority Order

Feature state resolves in this order (first match wins):

1. CLI override (--enable-feature, --disable-feature)
2. Config file (features.flags in config.json)
3. Default value (defined in code)

Available Features

API Reference

features.IsEnabled(name string) bool           // Check if enabled
features.List() map[string]bool                 // All features with current state
features.ListAll() []Feature                    // All features with metadata
features.SetEnabled(name string, enabled bool) error  // Persist to config
features.SetOverride(name string, enabled bool) // Runtime override (not persisted)
features.IsKnownFeature(name string) bool       // Check if registered

Best Practices

• Use snake_case for feature names (e.g., my_new_feature)
• New experimental features should default to false
• Provide clear descriptions for each feature
• Document features in docs/guides/feature-flags.md when adding them
• Remove feature flags once features are stable

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