Document feature flags

CONTRIBUTING.md

@@ -39,7 +39,7 @@ cargo test --all-features --all
 To build and open the documentation:
 
 ```sh
-cargo doc --lib --open
+cargo doc --all-features --lib --open
 ```
 
 Before performing the PR, once you have committed all changes, run:

src/event/types.rs

@@ -55,6 +55,6 @@ impl TryIntoTime for String {
 /// here.
 ///
 /// Also see:
-/// * https://github.com/cloudevents/spec/blob/v1.0.1/spec.md#type-system
-/// * https://tools.ietf.org/html/rfc3986#section-4.1
+/// * <https://github.com/cloudevents/spec/blob/v1.0.1/spec.md#type-system>
+/// * <https://tools.ietf.org/html/rfc3986#section-4.1>
 pub type UriReference = String;

src/lib.rs

@@ -31,6 +31,30 @@
 //! * Traits and utilities in [`message`] to implement Protocol Bindings
 //! * Feature-guarded modules for various Protocol Binding implementations, e.g. actix, reqwest, warp, rdkafka
 //!
+//! ## Feature flags
+//!
+//! Cloudevents uses a set of [feature flags] to conditionally compile
+//! only the module associated with the Protocol Binding you need:
+//!
+//! - `cloudevents-actix`: Enables the [actix] module. This
+//! extends the [`actix_web::HttpRequest`] with a
+//! [`to_event`](actix::HttpRequestExt::to_event) function, the
+//! [`actix_web::dev::HttpResponseBuilder`] with an
+//! [`event`](actix::HttpResponseBuilderExt::event) function,
+//! and implementations for [`actix_web::FromRequest`] and
+//! [`actix_web::Responder`] in order to take advantage of actix-web's
+//! [Extractors] and [Responders]
+//!
+//! - `cloudevents-reqwest`: Enables the [reqwest] module.
+//!
+//! - `cloudevents-warp`: Enables the [warp] module.
+//!
+//! - `cloudevents-rdkafka`: Enables the [rdkafka] module to
+//! seamlessly consume/produce cloudevents within Kafka messages.
+//!
+//! [feature flags]: https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section
+//! [Extractors]: https://actix.rs/docs/extractors/
+//! [Responders]: https://actix.rs/docs/handlers/
 
 #![deny(broken_intra_doc_links)]