Introduce ruff_index crate (#4597)

crates/ruff_index/src/slice.rs

@@ -0,0 +1,178 @@
+use crate::vec::IndexVec;
+use crate::Idx;
+use std::fmt::{Debug, Formatter};
+use std::marker::PhantomData;
+use std::ops::{Index, IndexMut};
+
+/// A view into contiguous `T`s, indexed by `I` rather than by `usize`.
+#[derive(PartialEq, Eq, Hash)]
+#[repr(transparent)]
+pub struct IndexSlice<I, T> {
+    index: PhantomData<I>,
+    pub raw: [T],
+}
+
+impl<I: Idx, T> IndexSlice<I, T> {
+    #[inline]
+    pub const fn empty() -> &'static Self {
+        Self::from_raw(&[])
+    }
+
+    #[inline]
+    pub const fn from_raw(raw: &[T]) -> &Self {
+        let ptr: *const [T] = raw;
+
+        #[allow(unsafe_code)]
+        // SAFETY: `IndexSlice` is `repr(transparent)` over a normal slice
+        unsafe {
+            &*(ptr as *const Self)
+        }
+    }
+
+    #[inline]
+    pub fn from_raw_mut(raw: &mut [T]) -> &mut Self {
+        let ptr: *mut [T] = raw;
+
+        #[allow(unsafe_code)]
+        // SAFETY: `IndexSlice` is `repr(transparent)` over a normal slice
+        unsafe {
+            &mut *(ptr as *mut Self)
+        }
+    }
+
+    #[inline]
+    pub const fn len(&self) -> usize {
+        self.raw.len()
+    }
+
+    #[inline]
+    pub const fn is_empty(&self) -> bool {
+        self.raw.is_empty()
+    }
+
+    #[inline]
+    pub fn iter(&self) -> std::slice::Iter<'_, T> {
+        self.raw.iter()
+    }
+
+    /// Returns an iterator over the indices
+    #[inline]
+    pub fn indices(
+        &self,
+    ) -> impl DoubleEndedIterator<Item = I> + ExactSizeIterator + Clone + 'static {
+        (0..self.len()).map(|n| I::new(n))
+    }
+
+    #[inline]
+    pub fn iter_mut(&mut self) -> std::slice::IterMut<'_, T> {
+        self.raw.iter_mut()
+    }
+
+    #[inline]
+    pub fn last_index(&self) -> Option<I> {
+        self.len().checked_sub(1).map(I::new)
+    }
+
+    #[inline]
+    pub fn swap(&mut self, a: I, b: I) {
+        self.raw.swap(a.index(), b.index());
+    }
+
+    #[inline]
+    pub fn get(&self, index: I) -> Option<&T> {
+        self.raw.get(index.index())
+    }
+
+    #[inline]
+    pub fn get_mut(&mut self, index: I) -> Option<&mut T> {
+        self.raw.get_mut(index.index())
+    }
+
+    #[inline]
+    pub fn binary_search(&self, value: &T) -> Result<I, I>
+    where
+        T: Ord,
+    {
+        match self.raw.binary_search(value) {
+            Ok(i) => Ok(Idx::new(i)),
+            Err(i) => Err(Idx::new(i)),
+        }
+    }
+}
+
+impl<I, T> Debug for IndexSlice<I, T>
+where
+    I: Idx,
+    T: Debug,
+{
+    fn fmt(&self, fmt: &mut Formatter<'_>) -> std::fmt::Result {
+        std::fmt::Debug::fmt(&self.raw, fmt)
+    }
+}
+
+impl<I: Idx, T> Index<I> for IndexSlice<I, T> {
+    type Output = T;
+
+    #[inline]
+    fn index(&self, index: I) -> &T {
+        &self.raw[index.index()]
+    }
+}
+
+impl<I: Idx, T> IndexMut<I> for IndexSlice<I, T> {
+    #[inline]
+    fn index_mut(&mut self, index: I) -> &mut T {
+        &mut self.raw[index.index()]
+    }
+}
+
+impl<'a, I: Idx, T> IntoIterator for &'a IndexSlice<I, T> {
+    type Item = &'a T;
+    type IntoIter = std::slice::Iter<'a, T>;
+
+    #[inline]
+    fn into_iter(self) -> std::slice::Iter<'a, T> {
+        self.raw.iter()
+    }
+}
+
+impl<'a, I: Idx, T> IntoIterator for &'a mut IndexSlice<I, T> {
+    type Item = &'a mut T;
+    type IntoIter = std::slice::IterMut<'a, T>;
+
+    #[inline]
+    fn into_iter(self) -> std::slice::IterMut<'a, T> {
+        self.raw.iter_mut()
+    }
+}
+
+impl<I: Idx, T: Clone> ToOwned for IndexSlice<I, T> {
+    type Owned = IndexVec<I, T>;
+
+    fn to_owned(&self) -> IndexVec<I, T> {
+        IndexVec::from_raw(self.raw.to_owned())
+    }
+
+    fn clone_into(&self, target: &mut IndexVec<I, T>) {
+        self.raw.clone_into(&mut target.raw);
+    }
+}
+
+impl<I: Idx, T> Default for &IndexSlice<I, T> {
+    #[inline]
+    fn default() -> Self {
+        IndexSlice::from_raw(Default::default())
+    }
+}
+
+impl<I: Idx, T> Default for &mut IndexSlice<I, T> {
+    #[inline]
+    fn default() -> Self {
+        IndexSlice::from_raw_mut(Default::default())
+    }
+}
+
+// Whether `IndexSlice` is `Send` depends only on the data,
+// not the phantom data.
+#[allow(unsafe_code)]
+unsafe impl<I: Idx, T> Send for IndexSlice<I, T> where T: Send {}