add-feature-flag

Add a new feature flag to gate code changes in the Warp codebase.

Overview

Feature flags in Warp are compile-time flags that allow features to be selectively enabled for different channels (e.g.: Dev, Stable). They use a small runtime plumbing layer that checks if a flag is enabled.

TUI note

The FeatureFlag enum (warp_core/src/features.rs) and the runtime FeatureFlag::X.is_enabled() check are SHARED by both front-ends: the GUI desktop app (app/) and the headless TUI (crates/warp_tui). The Cargo-feature steps in this skill (app/Cargo.toml, app/src/lib.rs) are GUI-app-specific. Prefer runtime is_enabled() checks so a flag works in both front-ends with no per-binary wiring. Only if you truly need a compile-time Cargo feature in the TUI, wire it into crates/warp_tui/Cargo.toml as well. Test the TUI with ./script/run-tui.

Steps

1. Add to Cargo.toml

Add the feature to app/Cargo.toml under the [features] section, but NOT under the default nested stanza:

toml
[features]
your_feature_name = []

2. Add to FeatureFlag enum

Add a new variant to the FeatureFlag enum in warp_core/src/features.rs:

rust
#[derive(Sequence)]
pub enum FeatureFlag {
    YourFeatureName,
}

3. Add conditional compilation directive

Add the feature to app/src/lib.rs with a corresponding #[cfg(feature = "...")] attribute to ensure it's only included when enabled:

rust
#[cfg(feature = "your_feature_name")]
YourFeatureName,

4. Gate code with runtime checks

In your code, use the runtime check to conditionally execute feature-gated code:

rust
if FeatureFlag::YourFeatureName.is_enabled() {
    // feature-gated behavior
}

5. (Optional) Enable for dogfood builds

To enable the feature by default for Dev/dogfood builds, add it to the DOGFOOD_FLAGS array in features.rs:

rust
pub const DOGFOOD_FLAGS: &[FeatureFlag] = &[
    FeatureFlag::YourFeatureName,
];

6. Running with feature flags

To test locally with the feature enabled:

bash
cargo run --features your_feature_name

# Multiple features:
cargo run --features your_feature_name,another_feature

Keybindings with Feature Flags

If adding an EditableBinding or FixedBinding that's part of a gated feature, include an enabled predicate that checks the feature flag. This prevents the keybinding from appearing in keyboard settings when the feature is disabled.

Example:

rust
EditableBinding::new(
    "action:name",
    "Action description",
    YourAction::Variant
)
.with_enabled(|| FeatureFlag::YourFeatureName.is_enabled())
.with_key_binding("cmdorctrl-key")

Rolling Out to Stable

When ready to enable the feature for all Warp Stable users, add it to the default array in app/Cargo.toml:

toml
[features]
default = [
    "your_feature_name",
    # other default features...
]

Best Practices

• Prefer runtime checks over cfg directives: Use FeatureFlag::YourFeatureName.is_enabled() instead of #[cfg(...)] when possible, so flags can be toggled without recompilation and are easier to clean up later
• Use #[cfg(...)] only when code cannot compile without the flag (e.g., platform-specific code or missing dependencies)
• Keep flags high-level and product-focused rather than per-call-site
• Remove flags and dead branches after launch has stabilized