fix feature settings

Cargo.toml

@@ -29,7 +29,6 @@ default = [
   "log",
   "num_cpus",
   "pin-project-lite",
-  "smol",
 ]
 docs = ["attributes", "unstable", "default"]
 unstable = ["std", "broadcaster"]
@@ -43,6 +42,7 @@ std = [
   "once_cell",
   "pin-utils",
   "slab",
+  "smol",
 ]
 alloc = [
   "futures-core/alloc",

src/utils.rs

@@ -59,14 +59,14 @@ pub(crate) trait Context {
     fn context(self, message: impl Fn() -> String) -> Self;
 }
 
-#[cfg(not(target_os = "unknown"))]
+#[cfg(all(not(target_os = "unknown"), feature = "default"))]
 pub(crate) type Timer = smol::Timer;
 
-#[cfg(target_arch = "wasm32")]
+#[cfg(all(target_arch = "wasm32", feature = "default"))]
 #[derive(Debug)]
 pub(crate) struct Timer(wasm_timer::Delay);
 
-#[cfg(target_arch = "wasm32")]
+#[cfg(all(target_arch = "wasm32", feature = "default"))]
 impl Timer {
     pub(crate) fn after(dur: std::time::Duration) -> Self {
         Timer(wasm_timer::Delay::new(dur))