refactor: use cfg-aliases for feature flags

build.rs

@@ -0,0 +1,77 @@
+fn main() {
+    // Add to the list of expected config names and values that is used when checking the reachable
+    // cfg expressions with the unexpected_cfgs lint.
+    //
+    // See https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-check-cfg
+    println!("cargo:rustc-check-cfg=cfg(http1)");
+    println!("cargo:rustc-check-cfg=cfg(http2)");
+    println!("cargo:rustc-check-cfg=cfg(client)");
+    println!("cargo:rustc-check-cfg=cfg(server)");
+    println!("cargo:rustc-check-cfg=cfg(ffi)");
+    println!("cargo:rustc-check-cfg=cfg(full)");
+    println!("cargo:rustc-check-cfg=cfg(nightly)");
+    println!("cargo:rustc-check-cfg=cfg(runtime)"); // TODO evaluate if this is needed (see below)
+    println!("cargo:rustc-check-cfg=cfg(tracing)");
+    println!("cargo:rustc-check-cfg=cfg(http_client)");
+    println!("cargo:rustc-check-cfg=cfg(http1_client)");
+    println!("cargo:rustc-check-cfg=cfg(http2_client)");
+    println!("cargo:rustc-check-cfg=cfg(http_server)");
+    println!("cargo:rustc-check-cfg=cfg(http1_server)");
+    println!("cargo:rustc-check-cfg=cfg(http2_server)");
+
+    // Add cfg flags that simplify using cfg expressions in the code. e.g. instead of
+    // `#[cfg(all(any(feature = "http1", feature = "http2"), feature = "server")]` you can use
+    // `#[cfg(http_server)]`
+    //
+    // See https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-cfg
+    #[cfg(feature = "http1")]
+    println!("cargo:rustc-cfg=http1");
+
+    #[cfg(feature = "http2")]
+    println!("cargo:rustc-cfg=http2");
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    println!("cargo:rustc-cfg=http");
+
+    #[cfg(feature = "client")]
+    println!("cargo:rustc-cfg=client");
+
+    #[cfg(feature = "server")]
+    println!("cargo:rustc-cfg=server");
+
+    #[cfg(feature = "ffi")]
+    println!("cargo:rustc-cfg=ffi");
+
+    #[cfg(feature = "full")]
+    println!("cargo:rustc-cfg=full");
+
+    #[cfg(feature = "nightly")]
+    println!("cargo:rustc-cfg=nightly");
+
+    // TODO: this feature doesn't actually exist in the cargo.toml
+    // this condition was added to simplify the conditions in src/mock.rs, but I'm not sure if those
+    // conditions were actually working as intended
+    // #[cfg(feature = "runtime")]
+    // println!("cargo:rustc-cfg=runtime");
+
+    #[cfg(feature = "tracing")]
+    println!("cargo:rustc-cfg=tracing");
+
+    #[cfg(all(any(feature = "http1", feature = "http2"), feature = "client"))]
+    println!("cargo:rustc-cfg=http_client");
+
+    #[cfg(all(feature = "http1", feature = "client"))]
+    println!("cargo:rustc-cfg=http1_client");
+
+    #[cfg(all(feature = "http2", feature = "client"))]
+    println!("cargo:rustc-cfg=http2_client");
+
+    #[cfg(all(any(feature = "http1", feature = "http2"), feature = "server"))]
+    println!("cargo:rustc-cfg=http_server");
+
+    #[cfg(all(feature = "http1", feature = "server"))]
+    println!("cargo:rustc-cfg=http1_server");
+
+    #[cfg(all(feature = "http2", feature = "server"))]
+    println!("cargo:rustc-cfg=http2_server");
+}

examples/hello-http2.rs

@@ -3,7 +3,7 @@
 
 use http_body_util::Full;
 use hyper::body::Bytes;
-#[cfg(feature = "server")]
+#[cfg(server)]
 use hyper::server::conn::http2;
 use hyper::service::service_fn;
 use hyper::{Request, Response};
@@ -19,7 +19,7 @@ use support::TokioIo;
 
 // An async function that consumes a request, does nothing with it and returns a
 // response.
-#[cfg(feature = "server")]
+#[cfg(server)]
 async fn hello(_: Request<hyper::body::Incoming>) -> Result<Response<Full<Bytes>>, Infallible> {
     Ok(Response::new(Full::new(Bytes::from("Hello, World!"))))
 }
@@ -42,7 +42,7 @@ where
     }
 }
 
-#[cfg(feature = "server")]
+#[cfg(server)]
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
     pretty_env_logger::init();
@@ -83,7 +83,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
     }
 }
 
-#[cfg(not(feature = "server"))]
+#[cfg(not(server))]
 fn main() {
     panic!("This example requires the 'server' feature to be enabled");
 }