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Make FlatMapInPlaceVec an unsafe trait. #155951

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Merged
rust-bors merged 1 commit into from
Apr 30, 2026
+10 −5
Merged

Make FlatMapInPlaceVec an unsafe trait. #155951

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15 changes: 10 additions & 5 deletions compiler/rustc_data_structures/src/flat_map_in_place.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -67,8 +67,13 @@ impl<V: FlatMapInPlaceVec> FlatMapInPlace<V::Elem> for V {
}
}

// A vec-like type must implement these operations to support `flat_map_in_place`.
pub trait FlatMapInPlaceVec {
/// A vec-like type must implement these operations to support `flat_map_in_place`.
///
/// # Safety
///
/// The memory safety of the unsafe block in `flat_map_in_place` relies on impls of this trait
/// implementing all the operations correctly.
pub unsafe trait FlatMapInPlaceVec {
type Elem;

fn len(&self) -> usize;
Expand All @@ -78,7 +83,7 @@ pub trait FlatMapInPlaceVec {
fn insert(&mut self, idx: usize, elem: Self::Elem);
}

impl<T> FlatMapInPlaceVec for Vec<T> {
unsafe impl<T> FlatMapInPlaceVec for Vec<T> {
type Elem = T;

fn len(&self) -> usize {
Expand All @@ -104,7 +109,7 @@ impl<T> FlatMapInPlaceVec for Vec<T> {
}
}

impl<T> FlatMapInPlaceVec for ThinVec<T> {
unsafe impl<T> FlatMapInPlaceVec for ThinVec<T> {
type Elem = T;

fn len(&self) -> usize {
Expand All @@ -130,7 +135,7 @@ impl<T> FlatMapInPlaceVec for ThinVec<T> {
}
}

impl<T, const N: usize> FlatMapInPlaceVec for SmallVec<[T; N]> {
unsafe impl<T, const N: usize> FlatMapInPlaceVec for SmallVec<[T; N]> {
type Elem = T;

fn len(&self) -> usize {
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