feature-flags

name: feature-flags description: 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. user-invocable: false

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

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

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

Add to the allFeatures slice:

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

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):

CLI override (--enable-feature, --disable-feature)
Config file (features.flags in config.json)
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

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