Vendor things

third-party/vendor/triomphe/src/arc_union.rs

@@ -0,0 +1,139 @@
+use core::fmt;
+use core::marker::PhantomData;
+use core::ptr;
+use core::usize;
+
+use super::{Arc, ArcBorrow};
+
+/// A tagged union that can represent `Arc<A>` or `Arc<B>` while only consuming a
+/// single word. The type is also `NonNull`, and thus can be stored in an Option
+/// without increasing size.
+///
+/// This is functionally equivalent to
+/// `enum ArcUnion<A, B> { First(Arc<A>), Second(Arc<B>)` but only takes up
+/// up a single word of stack space.
+///
+/// This could probably be extended to support four types if necessary.
+pub struct ArcUnion<A, B> {
+    p: ptr::NonNull<()>,
+    phantom_a: PhantomData<A>,
+    phantom_b: PhantomData<B>,
+}
+
+unsafe impl<A: Sync + Send, B: Send + Sync> Send for ArcUnion<A, B> {}
+unsafe impl<A: Sync + Send, B: Send + Sync> Sync for ArcUnion<A, B> {}
+
+impl<A: PartialEq, B: PartialEq> PartialEq for ArcUnion<A, B> {
+    fn eq(&self, other: &Self) -> bool {
+        use crate::ArcUnionBorrow::*;
+        match (self.borrow(), other.borrow()) {
+            (First(x), First(y)) => x == y,
+            (Second(x), Second(y)) => x == y,
+            (_, _) => false,
+        }
+    }
+}
+
+/// This represents a borrow of an `ArcUnion`.
+#[derive(Debug)]
+pub enum ArcUnionBorrow<'a, A: 'a, B: 'a> {
+    First(ArcBorrow<'a, A>),
+    Second(ArcBorrow<'a, B>),
+}
+
+impl<A, B> ArcUnion<A, B> {
+    unsafe fn new(ptr: *mut ()) -> Self {
+        ArcUnion {
+            p: ptr::NonNull::new_unchecked(ptr),
+            phantom_a: PhantomData,
+            phantom_b: PhantomData,
+        }
+    }
+
+    /// Returns true if the two values are pointer-equal.
+    #[inline]
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.p == other.p
+    }
+
+    /// Returns an enum representing a borrow of either A or B.
+    pub fn borrow(&self) -> ArcUnionBorrow<A, B> {
+        if self.is_first() {
+            let ptr = self.p.as_ptr() as *const A;
+            let borrow = unsafe { ArcBorrow::from_ref(&*ptr) };
+            ArcUnionBorrow::First(borrow)
+        } else {
+            let ptr = ((self.p.as_ptr() as usize) & !0x1) as *const B;
+            let borrow = unsafe { ArcBorrow::from_ref(&*ptr) };
+            ArcUnionBorrow::Second(borrow)
+        }
+    }
+
+    /// Creates an `ArcUnion` from an instance of the first type.
+    #[inline]
+    pub fn from_first(other: Arc<A>) -> Self {
+        unsafe { Self::new(Arc::into_raw(other) as *mut _) }
+    }
+
+    /// Creates an `ArcUnion` from an instance of the second type.
+    #[inline]
+    pub fn from_second(other: Arc<B>) -> Self {
+        unsafe { Self::new(((Arc::into_raw(other) as usize) | 0x1) as *mut _) }
+    }
+
+    /// Returns true if this `ArcUnion` contains the first type.
+    #[inline]
+    pub fn is_first(&self) -> bool {
+        self.p.as_ptr() as usize & 0x1 == 0
+    }
+
+    /// Returns true if this `ArcUnion` contains the second type.
+    #[inline]
+    pub fn is_second(&self) -> bool {
+        !self.is_first()
+    }
+
+    /// Returns a borrow of the first type if applicable, otherwise `None`.
+    pub fn as_first(&self) -> Option<ArcBorrow<A>> {
+        match self.borrow() {
+            ArcUnionBorrow::First(x) => Some(x),
+            ArcUnionBorrow::Second(_) => None,
+        }
+    }
+
+    /// Returns a borrow of the second type if applicable, otherwise None.
+    pub fn as_second(&self) -> Option<ArcBorrow<B>> {
+        match self.borrow() {
+            ArcUnionBorrow::First(_) => None,
+            ArcUnionBorrow::Second(x) => Some(x),
+        }
+    }
+}
+
+impl<A, B> Clone for ArcUnion<A, B> {
+    fn clone(&self) -> Self {
+        match self.borrow() {
+            ArcUnionBorrow::First(x) => ArcUnion::from_first(x.clone_arc()),
+            ArcUnionBorrow::Second(x) => ArcUnion::from_second(x.clone_arc()),
+        }
+    }
+}
+
+impl<A, B> Drop for ArcUnion<A, B> {
+    fn drop(&mut self) {
+        match self.borrow() {
+            ArcUnionBorrow::First(x) => unsafe {
+                let _ = Arc::from_raw(&*x);
+            },
+            ArcUnionBorrow::Second(x) => unsafe {
+                let _ = Arc::from_raw(&*x);
+            },
+        }
+    }
+}
+
+impl<A: fmt::Debug, B: fmt::Debug> fmt::Debug for ArcUnion<A, B> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.borrow(), f)
+    }
+}