7 files changed, 349 insertions, 43 deletions

diff --git a/Cargo.lock b/Cargo.lock
index c15955f4c..aac4d91b3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -752,6 +752,7 @@ dependencies = [
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "relative-path 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tempfile 3.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "thread_worker 0.1.0",
  "walkdir 2.2.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -779,6 +780,33 @@ dependencies = [
 ]
 
 [[package]]
+name = "rand"
+version = "0.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "cloudabi 0.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "fuchsia-zircon 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.45 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand_chacha 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand_core 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand_hc 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand_isaac 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand_pcg 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand_xorshift 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "rand_core 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "rand_core"
 version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -792,6 +820,39 @@ version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
+name = "rand_hc"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "rand_core 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "rand_isaac"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "rand_core 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "rand_pcg"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "rand_core 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "rand_xorshift"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "rand_core 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "rayon"
 version = "1.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1069,6 +1130,19 @@ dependencies = [
 ]
 
 [[package]]
+name = "tempfile"
+version = "3.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "cfg-if 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.45 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.6.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "redox_syscall 0.1.44 (registry+https://github.com/rust-lang/crates.io-index)",
+ "remove_dir_all 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "tera"
 version = "0.11.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1431,8 +1505,14 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum quote 0.6.10 (registry+https://github.com/rust-lang/crates.io-index)" = "53fa22a1994bd0f9372d7a816207d8a2677ad0325b073f5c5332760f0fb62b5c"
 "checksum rand 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "8356f47b32624fef5b3301c1be97e5944ecdd595409cc5da11d05f211db6cfbd"
 "checksum rand 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)" = "e464cd887e869cddcae8792a4ee31d23c7edd516700695608f5b98c67ee0131c"
+"checksum rand 0.6.1 (registry+https://github.com/rust-lang/crates.io-index)" = "ae9d223d52ae411a33cf7e54ec6034ec165df296ccd23533d671a28252b6f66a"
+"checksum rand_chacha 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "771b009e3a508cb67e8823dda454aaa5368c7bc1c16829fb77d3e980440dd34a"
 "checksum rand_core 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "1961a422c4d189dfb50ffa9320bf1f2a9bd54ecb92792fb9477f99a1045f3372"
 "checksum rand_core 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0905b6b7079ec73b314d4c748701f6931eb79fd97c668caa3f1899b22b32c6db"
+"checksum rand_hc 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "7b40677c7be09ae76218dc623efbf7b18e34bced3f38883af07bb75630a21bc4"
+"checksum rand_isaac 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "ded997c9d5f13925be2a6fd7e66bf1872597f759fd9dd93513dd7e92e5a5ee08"
+"checksum rand_pcg 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "086bd09a33c7044e56bb44d5bdde5a60e7f119a9e95b0775f545de759a32fe05"
+"checksum rand_xorshift 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "effa3fcaa47e18db002bdde6060944b6d2f9cfd8db471c30e873448ad9187be3"
 "checksum rayon 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "373814f27745b2686b350dd261bfd24576a6fb0e2c5919b3a2b6005f820b0473"
 "checksum rayon-core 1.4.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b055d1e92aba6877574d8fe604a63c8b5df60f60e5982bf7ccbb1338ea527356"
 "checksum redox_syscall 0.1.44 (registry+https://github.com/rust-lang/crates.io-index)" = "a84bcd297b87a545980a2d25a0beb72a1f490c31f0a9fde52fca35bfbb1ceb70"
@@ -1467,6 +1547,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum syn 0.15.23 (registry+https://github.com/rust-lang/crates.io-index)" = "9545a6a093a3f0bd59adb472700acc08cad3776f860f16a897dfce8c88721cbc"
 "checksum synstructure 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)" = "73687139bf99285483c96ac0add482c3776528beac1d97d444f6e91f203a2015"
 "checksum tempdir 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)" = "15f2b5fb00ccdf689e0149d1b1b3c03fead81c2b37735d812fa8bddbbf41b6d8"
+"checksum tempfile 3.0.5 (registry+https://github.com/rust-lang/crates.io-index)" = "7e91405c14320e5c79b3d148e1c86f40749a36e490642202a31689cb1a3452b2"
 "checksum tera 0.11.20 (registry+https://github.com/rust-lang/crates.io-index)" = "4b505279e19d8f7d24b1a9dc58327c9c36174b1a2c7ebdeac70792d017cb64f3"
 "checksum teraron 0.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "0d89ad4617d1dec55331067fadaa041e813479e1779616f3d3ce9308bf46184e"
 "checksum termion 1.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "689a3bdfaab439fd92bc87df5c4c78417d3cbe537487274e9b0b2dce76e92096"
diff --git a/crates/ra_lsp_server/tests/heavy_tests/support.rs b/crates/ra_lsp_server/tests/heavy_tests/support.rs
index 07a878a26..c14d287ca 100644
--- a/crates/ra_lsp_server/tests/heavy_tests/support.rs
+++ b/crates/ra_lsp_server/tests/heavy_tests/support.rs
@@ -174,11 +174,11 @@ impl Server {
 impl Drop for Server {
     fn drop(&mut self) {
         self.send_request::<Shutdown>(666, ());
-        let receiver = self.worker.take().unwrap().stop();
+        let receiver = self.worker.take().unwrap().shutdown();
         while let Some(msg) = recv_timeout(&receiver) {
             drop(msg);
         }
-        self.watcher.take().unwrap().stop().unwrap();
+        self.watcher.take().unwrap().shutdown().unwrap();
     }
 }
 
diff --git a/crates/ra_vfs/Cargo.toml b/crates/ra_vfs/Cargo.toml
index 9ce619a77..ccea8a866 100644
--- a/crates/ra_vfs/Cargo.toml
+++ b/crates/ra_vfs/Cargo.toml
@@ -12,3 +12,6 @@ crossbeam-channel = "0.2.4"
 log = "0.4.6"
 
 thread_worker = { path = "../thread_worker" }
+
+[dev-dependencies]
+tempfile = "3"
diff --git a/crates/ra_vfs/src/arena.rs b/crates/ra_vfs/src/arena.rs
index d6fad753b..6b42ae26d 100644
--- a/crates/ra_vfs/src/arena.rs
+++ b/crates/ra_vfs/src/arena.rs
@@ -1,5 +1,4 @@
 use std::{
-    hash::{Hash, Hasher},
     marker::PhantomData,
     ops::{Index, IndexMut},
 };
@@ -21,6 +20,12 @@ impl<ID: ArenaId, T> Arena<ID, T> {
         self.data.push(value);
         ID::from_u32(id)
     }
+    pub fn iter<'a>(&'a self) -> impl Iterator<Item = (ID, &'a T)> {
+        self.data
+            .iter()
+            .enumerate()
+            .map(|(idx, value)| (ID::from_u32(idx as u32), value))
+    }
 }
 
 impl<ID: ArenaId, T> Default for Arena<ID, T> {
diff --git a/crates/ra_vfs/src/io.rs b/crates/ra_vfs/src/io.rs
index c46760583..178c9beff 100644
--- a/crates/ra_vfs/src/io.rs
+++ b/crates/ra_vfs/src/io.rs
@@ -1,35 +1,26 @@
 use std::{
     fs,
     path::{Path, PathBuf},
-    thread::JoinHandle,
 };
 
 use walkdir::{DirEntry, WalkDir};
-use crossbeam_channel::{Sender, Receiver};
 use thread_worker::{WorkerHandle};
+use relative_path::RelativePathBuf;
 
 use crate::VfsRoot;
 
-pub(crate) enum Task {
-    ScanRoot {
-        root: VfsRoot,
-        path: PathBuf,
-        filter: Box<FnMut(&DirEntry) -> bool + Send>,
-    },
-}
-
-#[derive(Debug)]
-pub(crate) struct FileEvent {
+pub(crate) struct Task {
+    pub(crate) root: VfsRoot,
     pub(crate) path: PathBuf,
-    pub(crate) kind: FileEventKind,
+    pub(crate) filter: Box<Fn(&DirEntry) -> bool + Send>,
 }
 
-#[derive(Debug)]
-pub(crate) enum FileEventKind {
-    Add(String),
+pub struct TaskResult {
+    pub(crate) root: VfsRoot,
+    pub(crate) files: Vec<(RelativePathBuf, String)>,
 }
 
-pub(crate) type Worker = thread_worker::Worker<Task, (PathBuf, Vec<FileEvent>)>;
+pub(crate) type Worker = thread_worker::Worker<Task, TaskResult>;
 
 pub(crate) fn start() -> (Worker, WorkerHandle) {
     thread_worker::spawn("vfs", 128, |input_receiver, output_sender| {
@@ -39,17 +30,17 @@ pub(crate) fn start() -> (Worker, WorkerHandle) {
     })
 }
 
-fn handle_task(task: Task) -> (PathBuf, Vec<FileEvent>) {
-    let Task::ScanRoot { path, .. } = task;
+fn handle_task(task: Task) -> TaskResult {
+    let Task { root, path, filter } = task;
     log::debug!("loading {} ...", path.as_path().display());
-    let events = load_root(path.as_path());
+    let files = load_root(path.as_path(), &*filter);
     log::debug!("... loaded {}", path.as_path().display());
-    (path, events)
+    TaskResult { root, files }
 }
 
-fn load_root(path: &Path) -> Vec<FileEvent> {
+fn load_root(root: &Path, filter: &dyn Fn(&DirEntry) -> bool) -> Vec<(RelativePathBuf, String)> {
     let mut res = Vec::new();
-    for entry in WalkDir::new(path) {
+    for entry in WalkDir::new(root).into_iter().filter_entry(filter) {
         let entry = match entry {
             Ok(entry) => entry,
             Err(e) => {
@@ -71,10 +62,8 @@ fn load_root(path: &Path) -> Vec<FileEvent> {
                 continue;
             }
         };
-        res.push(FileEvent {
-            path: path.to_owned(),
-            kind: FileEventKind::Add(text),
-        })
+        let path = RelativePathBuf::from_path(path.strip_prefix(root).unwrap()).unwrap();
+        res.push((path.to_owned(), text))
     }
     res
 }
diff --git a/crates/ra_vfs/src/lib.rs b/crates/ra_vfs/src/lib.rs
index 8ce6b6ee0..792f722a7 100644
--- a/crates/ra_vfs/src/lib.rs
+++ b/crates/ra_vfs/src/lib.rs
@@ -15,14 +15,19 @@ mod arena;
 mod io;
 
 use std::{
+    mem,
     thread,
     cmp::Reverse,
     path::{Path, PathBuf},
     ffi::OsStr,
     sync::Arc,
+    fs,
 };
 
+use rustc_hash::{FxHashMap, FxHashSet};
 use relative_path::RelativePathBuf;
+use crossbeam_channel::Receiver;
+use walkdir::DirEntry;
 use thread_worker::{WorkerHandle};
 
 use crate::{
@@ -40,15 +45,25 @@ impl RootFilter {
     fn new(root: PathBuf) -> RootFilter {
         RootFilter {
             root,
-            file_filter: rs_extension_filter,
+            file_filter: has_rs_extension,
         }
     }
-    fn can_contain(&self, path: &Path) -> bool {
-        (self.file_filter)(path) && path.starts_with(&self.root)
+    /// Check if this root can contain `path`. NB: even if this returns
+    /// true, the `path` might actually be conained in some nested root.
+    fn can_contain(&self, path: &Path) -> Option<RelativePathBuf> {
+        if !(self.file_filter)(path) {
+            return None;
+        }
+        if !(path.starts_with(&self.root)) {
+            return None;
+        }
+        let path = path.strip_prefix(&self.root).unwrap();
+        let path = RelativePathBuf::from_path(path).unwrap();
+        Some(path)
     }
 }
 
-fn rs_extension_filter(p: &Path) -> bool {
+fn has_rs_extension(p: &Path) -> bool {
     p.extension() == Some(OsStr::new("rs"))
 }
 
@@ -82,10 +97,11 @@ struct VfsFileData {
     text: Arc<String>,
 }
 
-struct Vfs {
+pub struct Vfs {
     roots: Arena<VfsRoot, RootFilter>,
     files: Arena<VfsFile, VfsFileData>,
-    // pending_changes: Vec<PendingChange>,
+    root2files: FxHashMap<VfsRoot, FxHashSet<VfsFile>>,
+    pending_changes: Vec<VfsChange>,
     worker: io::Worker,
     worker_handle: WorkerHandle,
 }
@@ -97,33 +113,144 @@ impl Vfs {
         let mut res = Vfs {
             roots: Arena::default(),
             files: Arena::default(),
+            root2files: FxHashMap::default(),
             worker,
             worker_handle,
+            pending_changes: Vec::new(),
         };
 
         // A hack to make nesting work.
         roots.sort_by_key(|it| Reverse(it.as_os_str().len()));
-
-        for path in roots {
-            res.roots.alloc(RootFilter::new(path));
+        for (i, path) in roots.iter().enumerate() {
+            let root = res.roots.alloc(RootFilter::new(path.clone()));
+            let nested = roots[..i]
+                .iter()
+                .filter(|it| it.starts_with(path))
+                .map(|it| it.clone())
+                .collect::<Vec<_>>();
+            let filter = move |entry: &DirEntry| {
+                if entry.file_type().is_file() {
+                    has_rs_extension(entry.path())
+                } else {
+                    nested.iter().all(|it| it != entry.path())
+                }
+            };
+            let task = io::Task {
+                root,
+                path: path.clone(),
+                filter: Box::new(filter),
+            };
+            res.worker.inp.send(task);
         }
         res
     }
 
-    pub fn add_file_overlay(&mut self, path: &Path, content: String) {}
+    pub fn task_receiver(&self) -> &Receiver<io::TaskResult> {
+        &self.worker.out
+    }
+
+    pub fn handle_task(&mut self, task: io::TaskResult) {
+        let mut files = Vec::new();
+        for (path, text) in task.files {
+            let text = Arc::new(text);
+            let file = self.add_file(task.root, path.clone(), Arc::clone(&text));
+            files.push((file, path, text));
+        }
+        let change = VfsChange::AddRoot {
+            root: task.root,
+            files,
+        };
+        self.pending_changes.push(change);
+    }
 
-    pub fn change_file_overlay(&mut self, path: &Path, new_content: String) {}
+    pub fn add_file_overlay(&mut self, path: &Path, text: String) {
+        if let Some((root, path, file)) = self.find_root(path) {
+            let text = Arc::new(text);
+            let change = if let Some(file) = file {
+                self.change_file(file, Arc::clone(&text));
+                VfsChange::ChangeFile { file, text }
+            } else {
+                let file = self.add_file(root, path.clone(), Arc::clone(&text));
+                VfsChange::AddFile {
+                    file,
+                    text,
+                    root,
+                    path,
+                }
+            };
+            self.pending_changes.push(change);
+        }
+    }
 
-    pub fn remove_file_overlay(&mut self, path: &Path) {}
+    pub fn change_file_overlay(&mut self, path: &Path, new_text: String) {
+        if let Some((_root, _path, file)) = self.find_root(path) {
+            let file = file.expect("can't change a file which wasn't added");
+            let text = Arc::new(new_text);
+            self.change_file(file, Arc::clone(&text));
+            let change = VfsChange::ChangeFile { file, text };
+            self.pending_changes.push(change);
+        }
+    }
+
+    pub fn remove_file_overlay(&mut self, path: &Path) {
+        if let Some((root, path, file)) = self.find_root(path) {
+            let file = file.expect("can't remove a file which wasn't added");
+            let full_path = path.to_path(&self.roots[root].root);
+            let change = if let Ok(text) = fs::read_to_string(&full_path) {
+                let text = Arc::new(text);
+                self.change_file(file, Arc::clone(&text));
+                VfsChange::ChangeFile { file, text }
+            } else {
+                self.remove_file(file);
+                VfsChange::RemoveFile { file }
+            };
+            self.pending_changes.push(change);
+        }
+    }
 
     pub fn commit_changes(&mut self) -> Vec<VfsChange> {
-        unimplemented!()
+        mem::replace(&mut self.pending_changes, Vec::new())
     }
 
     pub fn shutdown(self) -> thread::Result<()> {
         let _ = self.worker.shutdown();
         self.worker_handle.shutdown()
     }
+
+    fn add_file(&mut self, root: VfsRoot, path: RelativePathBuf, text: Arc<String>) -> VfsFile {
+        let data = VfsFileData { root, path, text };
+        let file = self.files.alloc(data);
+        self.root2files
+            .entry(root)
+            .or_insert_with(FxHashSet::default)
+            .insert(file);
+        file
+    }
+
+    fn change_file(&mut self, file: VfsFile, new_text: Arc<String>) {
+        self.files[file].text = new_text;
+    }
+
+    fn remove_file(&mut self, file: VfsFile) {
+        //FIXME: use arena with removal
+        self.files[file].text = Default::default();
+        self.files[file].path = Default::default();
+        let root = self.files[file].root;
+        let removed = self.root2files.get_mut(&root).unwrap().remove(&file);
+        assert!(removed);
+    }
+
+    fn find_root(&self, path: &Path) -> Option<(VfsRoot, RelativePathBuf, Option<VfsFile>)> {
+        let (root, path) = self
+            .roots
+            .iter()
+            .find_map(|(root, data)| data.can_contain(path).map(|it| (root, it)))?;
+        let file = self.root2files[&root]
+            .iter()
+            .map(|&it| it)
+            .find(|&file| self.files[file].path == path);
+        Some((root, path, file))
+    }
 }
 
 #[derive(Debug, Clone)]
diff --git a/crates/ra_vfs/tests/vfs.rs b/crates/ra_vfs/tests/vfs.rs
new file mode 100644
index 000000000..4f44215c8
--- /dev/null
+++ b/crates/ra_vfs/tests/vfs.rs
@@ -0,0 +1,101 @@
+use std::{
+    fs,
+    collections::HashSet,
+};
+
+use tempfile::tempdir;
+
+use ra_vfs::{Vfs, VfsChange};
+
+#[test]
+fn test_vfs_works() -> std::io::Result<()> {
+    let files = [
+        ("a/foo.rs", "hello"),
+        ("a/bar.rs", "world"),
+        ("a/b/baz.rs", "nested hello"),
+    ];
+
+    let dir = tempdir()?;
+    for (path, text) in files.iter() {
+        let file_path = dir.path().join(path);
+        fs::create_dir_all(file_path.parent().unwrap())?;
+        fs::write(file_path, text)?
+    }
+
+    let a_root = dir.path().join("a");
+    let b_root = dir.path().join("a/b");
+
+    let mut vfs = Vfs::new(vec![a_root, b_root]);
+    for _ in 0..2 {
+        let task = vfs.task_receiver().recv().unwrap();
+        vfs.handle_task(task);
+    }
+    {
+        let files = vfs
+            .commit_changes()
+            .into_iter()
+            .flat_map(|change| {
+                let files = match change {
+                    VfsChange::AddRoot { files, .. } => files,
+                    _ => panic!("unexpected change"),
+                };
+                files.into_iter().map(|(_id, path, text)| {
+                    let text: String = (&*text).clone();
+                    (format!("{}", path.display()), text)
+                })
+            })
+            .collect::<HashSet<_>>();
+
+        let expected_files = [
+            ("foo.rs", "hello"),
+            ("bar.rs", "world"),
+            ("baz.rs", "nested hello"),
+        ]
+        .iter()
+        .map(|(path, text)| (path.to_string(), text.to_string()))
+        .collect::<HashSet<_>>();
+
+        assert_eq!(files, expected_files);
+    }
+
+    vfs.add_file_overlay(&dir.path().join("a/b/baz.rs"), "quux".to_string());
+    let change = vfs.commit_changes().pop().unwrap();
+    match change {
+        VfsChange::ChangeFile { text, .. } => assert_eq!(&*text, "quux"),
+        _ => panic!("unexpected change"),
+    }
+
+    vfs.change_file_overlay(&dir.path().join("a/b/baz.rs"), "m".to_string());
+    let change = vfs.commit_changes().pop().unwrap();
+    match change {
+        VfsChange::ChangeFile { text, .. } => assert_eq!(&*text, "m"),
+        _ => panic!("unexpected change"),
+    }
+
+    vfs.remove_file_overlay(&dir.path().join("a/b/baz.rs"));
+    let change = vfs.commit_changes().pop().unwrap();
+    match change {
+        VfsChange::ChangeFile { text, .. } => assert_eq!(&*text, "nested hello"),
+        _ => panic!("unexpected change"),
+    }
+
+    vfs.add_file_overlay(&dir.path().join("a/b/spam.rs"), "spam".to_string());
+    let change = vfs.commit_changes().pop().unwrap();
+    match change {
+        VfsChange::AddFile { text, path, .. } => {
+            assert_eq!(&*text, "spam");
+            assert_eq!(path, "spam.rs");
+        }
+        _ => panic!("unexpected change"),
+    }
+
+    vfs.remove_file_overlay(&dir.path().join("a/b/spam.rs"));
+    let change = vfs.commit_changes().pop().unwrap();
+    match change {
+        VfsChange::RemoveFile { .. } => (),
+        _ => panic!("unexpected change"),
+    }
+
+    vfs.shutdown().unwrap();
+    Ok(())
+}