New VFS API

crates/vfs/src/path_interner.rs

@@ -0,0 +1,31 @@
+//! 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 rustc_hash::FxHashMap;
+
+use crate::{FileId, VfsPath};
+
+#[derive(Default)]
+pub(crate) struct PathInterner {
+    map: FxHashMap<VfsPath, FileId>,
+    vec: Vec<VfsPath>,
+}
+
+impl PathInterner {
+    pub(crate) fn get(&self, path: &VfsPath) -> Option<FileId> {
+        self.map.get(path).copied()
+    }
+    pub(crate) fn intern(&mut self, path: VfsPath) -> FileId {
+        if let Some(id) = self.get(&path) {
+            return id;
+        }
+        let id = FileId(self.vec.len() as u32);
+        self.map.insert(path.clone(), id);
+        self.vec.push(path);
+        id
+    }
+
+    pub(crate) fn lookup(&self, id: FileId) -> &VfsPath {
+        &self.vec[id.0 as usize]
+    }
+}