1 files changed, 48 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/vfs/src/path_interner.rs b/src/tools/rust-analyzer/crates/vfs/src/path_interner.rs
new file mode 100644
index 000000000..6e049f0d4
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/vfs/src/path_interner.rs
@@ -0,0 +1,48 @@
+//! Maps paths to compact integer ids. We don't care about clearings paths which
+//! no longer exist -- the assumption is total size of paths we ever look at is
+//! not too big.
+use std::hash::BuildHasherDefault;
+
+use indexmap::IndexSet;
+use rustc_hash::FxHasher;
+
+use crate::{FileId, VfsPath};
+
+/// Structure to map between [`VfsPath`] and [`FileId`].
+pub(crate) struct PathInterner {
+    map: IndexSet<VfsPath, BuildHasherDefault<FxHasher>>,
+}
+
+impl Default for PathInterner {
+    fn default() -> Self {
+        Self { map: IndexSet::default() }
+    }
+}
+
+impl PathInterner {
+    /// Get the id corresponding to `path`.
+    ///
+    /// If `path` does not exists in `self`, returns [`None`].
+    pub(crate) fn get(&self, path: &VfsPath) -> Option<FileId> {
+        self.map.get_index_of(path).map(|i| FileId(i as u32))
+    }
+
+    /// Insert `path` in `self`.
+    ///
+    /// - If `path` already exists in `self`, returns its associated id;
+    /// - Else, returns a newly allocated id.
+    pub(crate) fn intern(&mut self, path: VfsPath) -> FileId {
+        let (id, _added) = self.map.insert_full(path);
+        assert!(id < u32::MAX as usize);
+        FileId(id as u32)
+    }
+
+    /// Returns the path corresponding to `id`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `id` does not exists in `self`.
+    pub(crate) fn lookup(&self, id: FileId) -> &VfsPath {
+        self.map.get_index(id.0 as usize).unwrap()
+    }
+}