Merge branch 'master' into stabilize-vecdeque-make_contiguous

1 files changed, 82 insertions, 0 deletions

diff --git a/compiler/rustc_data_structures/src/thin_vec.rs b/compiler/rustc_data_structures/src/thin_vec.rs
new file mode 100644
index 00000000000..4d673fd5cf9
--- /dev/null
+++ b/compiler/rustc_data_structures/src/thin_vec.rs
@@ -0,0 +1,82 @@
+use crate::stable_hasher::{HashStable, StableHasher};
+
+/// A vector type optimized for cases where this size is usually 0 (cf. `SmallVector`).
+/// The `Option<Box<..>>` wrapping allows us to represent a zero sized vector with `None`,
+/// which uses only a single (null) pointer.
+#[derive(Clone, Encodable, Decodable, Debug)]
+pub struct ThinVec<T>(Option<Box<Vec<T>>>);
+
+impl<T> ThinVec<T> {
+    pub fn new() -> Self {
+        ThinVec(None)
+    }
+}
+
+impl<T> From<Vec<T>> for ThinVec<T> {
+    fn from(vec: Vec<T>) -> Self {
+        if vec.is_empty() { ThinVec(None) } else { ThinVec(Some(Box::new(vec))) }
+    }
+}
+
+impl<T> Into<Vec<T>> for ThinVec<T> {
+    fn into(self) -> Vec<T> {
+        match self {
+            ThinVec(None) => Vec::new(),
+            ThinVec(Some(vec)) => *vec,
+        }
+    }
+}
+
+impl<T> ::std::ops::Deref for ThinVec<T> {
+    type Target = [T];
+    fn deref(&self) -> &[T] {
+        match *self {
+            ThinVec(None) => &[],
+            ThinVec(Some(ref vec)) => vec,
+        }
+    }
+}
+
+impl<T> ::std::ops::DerefMut for ThinVec<T> {
+    fn deref_mut(&mut self) -> &mut [T] {
+        match *self {
+            ThinVec(None) => &mut [],
+            ThinVec(Some(ref mut vec)) => vec,
+        }
+    }
+}
+
+impl<T> Extend<T> for ThinVec<T> {
+    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+        match *self {
+            ThinVec(Some(ref mut vec)) => vec.extend(iter),
+            ThinVec(None) => *self = iter.into_iter().collect::<Vec<_>>().into(),
+        }
+    }
+
+    fn extend_one(&mut self, item: T) {
+        match *self {
+            ThinVec(Some(ref mut vec)) => vec.push(item),
+            ThinVec(None) => *self = vec![item].into(),
+        }
+    }
+
+    fn extend_reserve(&mut self, additional: usize) {
+        match *self {
+            ThinVec(Some(ref mut vec)) => vec.reserve(additional),
+            ThinVec(None) => *self = Vec::with_capacity(additional).into(),
+        }
+    }
+}
+
+impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ThinVec<T> {
+    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
+        (**self).hash_stable(hcx, hasher)
+    }
+}
+
+impl<T> Default for ThinVec<T> {
+    fn default() -> Self {
+        Self(None)
+    }
+}