2 files changed, 45 insertions, 0 deletions
diff --git a/compiler/rustc_data_structures/src/sync.rs b/compiler/rustc_data_structures/src/sync.rs
index ad71dcdf9d9..31323c21df0 100644
--- a/compiler/rustc_data_structures/src/sync.rs
+++ b/compiler/rustc_data_structures/src/sync.rs
@@ -26,6 +26,10 @@ use std::panic::{catch_unwind, resume_unwind, AssertUnwindSafe};
 pub use std::sync::atomic::Ordering;
 pub use std::sync::atomic::Ordering::SeqCst;
 
+pub use vec::AppendOnlyVec;
+
+mod vec;
+
 cfg_if! {
     if #[cfg(not(parallel_compiler))] {
         pub auto trait Send {}
diff --git a/compiler/rustc_data_structures/src/sync/vec.rs b/compiler/rustc_data_structures/src/sync/vec.rs
new file mode 100644
index 00000000000..cbea4f05999
--- /dev/null
+++ b/compiler/rustc_data_structures/src/sync/vec.rs
@@ -0,0 +1,41 @@
+use std::marker::PhantomData;
+
+use rustc_index::vec::Idx;
+
+pub struct AppendOnlyVec<I: Idx, T: Copy> {
+    #[cfg(not(parallel_compiler))]
+    vec: elsa::vec::FrozenVec<T>,
+    #[cfg(parallel_compiler)]
+    vec: elsa::sync::LockFreeFrozenVec<T>,
+    _marker: PhantomData<fn(&I)>,
+}
+
+impl<I: Idx, T: Copy> AppendOnlyVec<I, T> {
+    pub fn new() -> Self {
+        Self {
+            #[cfg(not(parallel_compiler))]
+            vec: elsa::vec::FrozenVec::new(),
+            #[cfg(parallel_compiler)]
+            vec: elsa::sync::LockFreeFrozenVec::new(),
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn push(&self, val: T) -> I {
+        #[cfg(not(parallel_compiler))]
+        let i = self.vec.len();
+        #[cfg(not(parallel_compiler))]
+        self.vec.push(val);
+        #[cfg(parallel_compiler)]
+        let i = self.vec.push(val);
+        I::new(i)
+    }
+
+    pub fn get(&self, i: I) -> Option<T> {
+        let i = i.index();
+        #[cfg(not(parallel_compiler))]
+        return self.vec.get_copy(i);
+        #[cfg(parallel_compiler)]
+        return self.vec.get(i);
+    }
+}