Add basic tests for OwnedSlice

Author: WaffleLapkin

compiler/rustc_data_structures/src/owned_slice.rs

@@ -111,3 +111,6 @@ unsafe impl Send for OwnedSlice {}
 
 // Safety: `OwnedSlice` is conceptually `(&'self.1 [u8], Box<dyn Send + Sync>)`, which is `Sync`
 unsafe impl Sync for OwnedSlice {}
+
+#[cfg(test)]
+mod tests;

compiler/rustc_data_structures/src/owned_slice/tests.rs

@@ -0,0 +1,68 @@
+use std::{cell::Cell, ops::Deref, rc::Rc};
+
+use crate::{
+    owned_slice::{slice_owned, try_slice_owned, OwnedSlice},
+    OnDrop,
+};
+
+#[test]
+fn smoke() {
+    let slice = slice_owned(vec![1, 2, 3, 4, 5, 6], Vec::as_slice);
+
+    assert_eq!(&*slice, [1, 2, 3, 4, 5, 6]);
+}
+
+#[test]
+fn static_storage() {
+    let slice = slice_owned(Box::new(String::from("what")), |_| b"bytes boo");
+
+    assert_eq!(&*slice, b"bytes boo");
+}
+
+#[test]
+fn slice_the_slice() {
+    let slice = slice_owned(vec![1, 2, 3, 4, 5, 6], Vec::as_slice);
+    let slice = slice_owned(slice, |s| &s[1..][..4]);
+    let slice = slice_owned(slice, |s| s);
+    let slice = slice_owned(slice, |s| &s[1..]);
+
+    assert_eq!(&*slice, &[1, 2, 3, 4, 5, 6][1..][..4][1..]);
+}
+
+#[test]
+fn try_and_fail() {
+    let res = try_slice_owned(vec![0], |v| v.get(12..).ok_or(()));
+
+    assert!(res.is_err());
+}
+
+#[test]
+fn boxed() {
+    // It's important that we don't cause UB because of `Box`'es uniqueness
+
+    let boxed: Box<[u8]> = vec![1, 1, 2, 3, 5, 8, 13, 21].into_boxed_slice();
+    let slice = slice_owned(boxed, Deref::deref);
+
+    assert_eq!(&*slice, [1, 1, 2, 3, 5, 8, 13, 21]);
+}
+
+#[test]
+fn drop() {
+    let flag = Rc::new(Cell::new(false));
+    let flag_prime = Rc::clone(&flag);
+    let d = OnDrop(move || flag_prime.set(true));
+
+    let slice = slice_owned(d, |_| &[]);
+
+    assert_eq!(flag.get(), false);
+
+    std::mem::drop(slice);
+
+    assert_eq!(flag.get(), true);
+}
+
+#[test]
+fn send_sync() {
+    crate::sync::assert_send::<OwnedSlice>();
+    crate::sync::assert_sync::<OwnedSlice>();
+}