Agent skill

feature-flags

Creating and using feature flags in sidecar for gating experimental functionality. Covers flag registration, checking flags in code, config file and CLI overrides, and priority resolution. Use when adding feature flags, toggling features, or gating new functionality behind flags.

View SKILL.md on GitHub Repository
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Install this agent skill to your Project

npx add-skill https://github.com/marcus/sidecar/tree/main/.claude/skills/feature-flags

SKILL.md

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

go
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:
go
var MyNewFeature = Feature{
    Name:        "my_new_feature",
    Default:     false,
    Description: "Description of what this enables",
}
  1. Add to the allFeatures slice:
go
var allFeatures = []Feature{
    TmuxInteractiveInput,
    MyNewFeature, // Add here
}
  1. Use the feature check in your code:
go
if features.IsEnabled("my_new_feature") {
    // New functionality
}

User Configuration

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

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

CLI override (takes precedence over config)

bash
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

Feature Default Description
tmux_interactive_input true Write support for tmux panes
tmux_inline_edit true Inline file editing via tmux in files plugin
notes_plugin false Notes plugin for capturing quick notes

API Reference

go
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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