Throw compile time error for missing runtime

.github/workflows/rust.yml

@@ -171,7 +171,7 @@ jobs:
           components: rustfmt, clippy
       - uses: Swatinem/rust-cache@v2
       - run: cargo fmt --all -- --check
-      - run: cargo check --locked --manifest-path quinn/Cargo.toml --all-targets --no-default-features
+      - run: cargo check --locked --manifest-path quinn/Cargo.toml --all-targets --no-default-features --features runtime-tokio
       - run: cargo clippy --locked --all-targets -- -D warnings
       - uses: dtolnay/rust-toolchain@stable
         with:

quinn/Cargo.toml

@@ -37,7 +37,8 @@ rustls-ring = ["dep:rustls", "ring", "proto/rustls-ring", "proto/ring"]
 ring = ["proto/ring"]
 runtime-tokio = ["tokio/time", "tokio/rt", "tokio/net"]
 runtime-smol = ["dep:async-io", "dep:smol"]
-
+# Allow users to declare a custom runtimne
+custom-runtime = []
 # Configure `tracing` to log events via `log` if no `tracing` subscriber exists.
 tracing-log = ["tracing/log", "proto/tracing-log", "udp/tracing-log"]
 # Enable rustls logging

quinn/src/runtime/mod.rs

@@ -13,6 +13,9 @@ use udp::{RecvMeta, Transmit};
 
 use crate::Instant;
 
+#[cfg(not(any(feature = "runtime-tokio", feature = "runtime-smol", feature = "custom-runtime")))]
+compile_error!("no async runtime found. Please enable a runtime feature such as runtime-tokio, runtime-smol or custom-runtime");
+
 /// Abstracts I/O and timer operations for runtime independence
 pub trait Runtime: Send + Sync + Debug + 'static {
     /// Construct a timer that will expire at `i`