1 files changed, 75 insertions, 0 deletions
diff --git a/library/proc_macro/src/bridge/handle.rs b/library/proc_macro/src/bridge/handle.rs
new file mode 100644
index 000000000..00954107b
--- /dev/null
+++ b/library/proc_macro/src/bridge/handle.rs
@@ -0,0 +1,75 @@
+//! Server-side handles and storage for per-handle data.
+
+use std::collections::BTreeMap;
+use std::hash::Hash;
+use std::num::NonZeroU32;
+use std::ops::{Index, IndexMut};
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+use super::fxhash::FxHashMap;
+
+pub(super) type Handle = NonZeroU32;
+
+/// A store that associates values of type `T` with numeric handles. A value can
+/// be looked up using its handle.
+pub(super) struct OwnedStore<T: 'static> {
+    counter: &'static AtomicUsize,
+    data: BTreeMap<Handle, T>,
+}
+
+impl<T> OwnedStore<T> {
+    pub(super) fn new(counter: &'static AtomicUsize) -> Self {
+        // Ensure the handle counter isn't 0, which would panic later,
+        // when `NonZeroU32::new` (aka `Handle::new`) is called in `alloc`.
+        assert_ne!(counter.load(Ordering::SeqCst), 0);
+
+        OwnedStore { counter, data: BTreeMap::new() }
+    }
+}
+
+impl<T> OwnedStore<T> {
+    pub(super) fn alloc(&mut self, x: T) -> Handle {
+        let counter = self.counter.fetch_add(1, Ordering::SeqCst);
+        let handle = Handle::new(counter as u32).expect("`proc_macro` handle counter overflowed");
+        assert!(self.data.insert(handle, x).is_none());
+        handle
+    }
+
+    pub(super) fn take(&mut self, h: Handle) -> T {
+        self.data.remove(&h).expect("use-after-free in `proc_macro` handle")
+    }
+}
+
+impl<T> Index<Handle> for OwnedStore<T> {
+    type Output = T;
+    fn index(&self, h: Handle) -> &T {
+        self.data.get(&h).expect("use-after-free in `proc_macro` handle")
+    }
+}
+
+impl<T> IndexMut<Handle> for OwnedStore<T> {
+    fn index_mut(&mut self, h: Handle) -> &mut T {
+        self.data.get_mut(&h).expect("use-after-free in `proc_macro` handle")
+    }
+}
+
+/// Like `OwnedStore`, but avoids storing any value more than once.
+pub(super) struct InternedStore<T: 'static> {
+    owned: OwnedStore<T>,
+    interner: FxHashMap<T, Handle>,
+}
+
+impl<T: Copy + Eq + Hash> InternedStore<T> {
+    pub(super) fn new(counter: &'static AtomicUsize) -> Self {
+        InternedStore { owned: OwnedStore::new(counter), interner: FxHashMap::default() }
+    }
+
+    pub(super) fn alloc(&mut self, x: T) -> Handle {
+        let owned = &mut self.owned;
+        *self.interner.entry(x).or_insert_with(|| owned.alloc(x))
+    }
+
+    pub(super) fn copy(&mut self, h: Handle) -> T {
+        self.owned[h]
+    }
+}