cap-std-sync: test opening a tempdir as ambient and then WasiDir

Cargo.lock

@@ -3075,6 +3075,7 @@ dependencies = [
  "lazy_static",
  "libc",
  "system-interface",
+ "tempfile",
  "tracing",
  "unsafe-io",
  "wasi-common",

crates/wasi-common/cap-std-sync/Cargo.toml

@@ -31,3 +31,6 @@ libc = "0.2"
 [target.'cfg(windows)'.dependencies]
 winapi = "0.3"
 lazy_static = "1.4"
+
+[dev-dependencies]
+tempfile = "3.1.0"

crates/wasi-common/cap-std-sync/src/dir.rs

@@ -1,4 +1,4 @@
-use crate::file::{filetype_from, to_sysif_fdflags, File};
+use crate::file::{filetype_from, File};
 use cap_fs_ext::{DirExt, MetadataExt, SystemTimeSpec};
 use std::any::Any;
 use std::convert::TryInto;
@@ -256,3 +256,20 @@ fn convert_systimespec(t: Option<wasi_common::SystemTimeSpec>) -> Option<SystemT
         None => None,
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::Dir;
+    #[test]
+    fn scratch_dir() {
+        let tempdir = tempfile::Builder::new()
+            .prefix("cap-std-sync")
+            .tempdir()
+            .expect("create temporary dir");
+        let preopen_dir = unsafe { cap_std::fs::Dir::open_ambient_dir(tempdir.path()) }
+            .expect("open ambient temporary dir");
+        let preopen_dir = Dir::from_cap_std(preopen_dir);
+        wasi_common::WasiDir::open_dir(&preopen_dir, false, ".")
+            .expect("open the same directory via WasiDir abstraction");
+    }
+}