1 files changed, 121 insertions, 0 deletions
diff --git a/third_party/rust/fallible_collections/src/boxed.rs b/third_party/rust/fallible_collections/src/boxed.rs
new file mode 100644
index 0000000000..9de6b3f446
--- /dev/null
+++ b/third_party/rust/fallible_collections/src/boxed.rs
@@ -0,0 +1,121 @@
+//! Implement Fallible Box
+use super::TryClone;
+use crate::TryReserveError;
+use alloc::alloc::Layout;
+use alloc::boxed::Box;
+use core::borrow::Borrow;
+use core::ptr::NonNull;
+
+/// trait to implement Fallible Box
+pub trait FallibleBox<T> {
+    /// try creating a new box, returning a Result<Box<T>,
+    /// TryReserveError> if allocation failed
+    fn try_new(t: T) -> Result<Self, TryReserveError>
+    where
+        Self: Sized;
+}
+/// TryBox is a thin wrapper around alloc::boxed::Box to provide support for
+/// fallible allocation.
+///
+/// See the crate documentation for more.
+pub struct TryBox<T> {
+    inner: Box<T>,
+}
+
+impl<T> TryBox<T> {
+    pub fn try_new(t: T) -> Result<Self, TryReserveError> {
+        Ok(Self {
+            inner: Box::try_new(t)?,
+        })
+    }
+
+    pub fn into_raw(b: TryBox<T>) -> *mut T {
+        Box::into_raw(b.inner)
+    }
+
+    /// # Safety
+    ///
+    /// See std::boxed::from_raw
+    pub unsafe fn from_raw(raw: *mut T) -> Self {
+        Self {
+            inner: Box::from_raw(raw),
+        }
+    }
+}
+
+impl<T: TryClone> TryClone for TryBox<T> {
+    fn try_clone(&self) -> Result<Self, TryReserveError> {
+        let clone: T = (*self.inner).try_clone()?;
+        Self::try_new(clone)
+    }
+}
+
+fn alloc(layout: Layout) -> Result<NonNull<u8>, TryReserveError> {
+    #[cfg(feature = "unstable")] // requires allocator_api
+    {
+        use core::alloc::AllocRef as _;
+        let mut g = alloc::alloc::Global;
+        g.alloc(layout, alloc::alloc::AllocInit::Uninitialized)
+            .map_err(|_e| TryReserveError::AllocError {
+                layout,
+                non_exhaustive: (),
+            })
+            .map(|memory_block| memory_block.ptr)
+    }
+    #[cfg(not(feature = "unstable"))]
+    {
+        match layout.size() {
+            0 => {
+                // Required for alloc safety
+                // See https://doc.rust-lang.org/stable/std/alloc/trait.GlobalAlloc.html#safety-1
+                Ok(NonNull::dangling())
+            }
+            1..=core::usize::MAX => {
+                let ptr = unsafe { alloc::alloc::alloc(layout) };
+                core::ptr::NonNull::new(ptr).ok_or(TryReserveError::AllocError { layout })
+            }
+            _ => unreachable!("size must be non-negative"),
+        }
+    }
+}
+
+impl<T> FallibleBox<T> for Box<T> {
+    fn try_new(t: T) -> Result<Self, TryReserveError> {
+        let layout = Layout::for_value(&t);
+        let ptr = alloc(layout)?.as_ptr() as *mut T;
+        unsafe {
+            core::ptr::write(ptr, t);
+            Ok(Box::from_raw(ptr))
+        }
+    }
+}
+
+impl<T: TryClone> TryClone for Box<T> {
+    fn try_clone(&self) -> Result<Self, TryReserveError> {
+        Self::try_new(Borrow::<T>::borrow(self).try_clone()?)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn boxed() {
+        let mut v = Box::try_new(5).unwrap();
+        assert_eq!(*v, 5);
+        *v = 3;
+        assert_eq!(*v, 3);
+    }
+    // #[test]
+    // fn big_alloc() {
+    //     let layout = Layout::from_size_align(1_000_000_000_000, 8).unwrap();
+    //     let ptr = unsafe { alloc::alloc::alloc(layout) };
+    //     assert!(ptr.is_null());
+    // }
+
+    #[test]
+    fn trybox_zst() {
+        let b = Box::try_new(()).expect("ok");
+        assert_eq!(b, Box::new(()));
+    }
+}