fix build with -default +unstable

and add a CI check for it

Fixes #842

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>

.github/workflows/ci.yml

@@ -86,6 +86,12 @@ jobs:
         command:  check
         args: --features attributes
 
+    - name: build unstable only
+      uses: actions-rs/cargo@v1
+      with:
+        command:  build
+        args: --no-default-features --features unstable
+
     - name: tests
       uses: actions-rs/cargo@v1
       with:

src/os/windows/mod.rs

@@ -5,5 +5,6 @@ cfg_std! {
 }
 
 cfg_unstable! {
+    #[cfg(feature = "default")]
     pub mod fs;
 }

src/utils.rs

@@ -66,7 +66,7 @@ mod timer {
 
 #[cfg(any(feature = "unstable", feature = "default"))]
 pub(crate) fn timer_after(dur: std::time::Duration) -> timer::Timer {
-    #[cfg(not(target_os = "unknown"))]
+    #[cfg(all(not(target_os = "unknown"), feature = "default"))]
     once_cell::sync::Lazy::force(&crate::rt::RUNTIME);
 
     Timer::after(dur)