6 files changed, 321 insertions, 4 deletions

diff --git a/crates/vfs/src/anchored_path.rs b/crates/vfs/src/anchored_path.rs
index 02720a32e..db15a2a21 100644
--- a/crates/vfs/src/anchored_path.rs
+++ b/crates/vfs/src/anchored_path.rs
@@ -26,14 +26,24 @@
 //! from the anchor than.
 use crate::FileId;
 
+/// Path relative to a file.
+///
+/// Owned version of [`AnchoredPath`].
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct AnchoredPathBuf {
+    /// File that this path is relative to.
     pub anchor: FileId,
+    /// Path relative to `anchor`'s containing directory.
     pub path: String,
 }
 
+/// Path relative to a file.
+///
+/// Borrowed version of [`AnchoredPathBuf`].
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
 pub struct AnchoredPath<'a> {
+    /// File that this path is relative to.
     pub anchor: FileId,
+    /// Path relative to `anchor`'s containing directory.
     pub path: &'a str,
 }
diff --git a/crates/vfs/src/file_set.rs b/crates/vfs/src/file_set.rs
index 49ca593ac..0a4590c8d 100644
--- a/crates/vfs/src/file_set.rs
+++ b/crates/vfs/src/file_set.rs
@@ -9,6 +9,7 @@ use rustc_hash::FxHashMap;
 
 use crate::{AnchoredPath, FileId, Vfs, VfsPath};
 
+/// A set of [`VfsPath`]s identified by [`FileId`]s.
 #[derive(Default, Clone, Eq, PartialEq)]
 pub struct FileSet {
     files: FxHashMap<VfsPath, FileId>,
@@ -16,9 +17,15 @@ pub struct FileSet {
 }
 
 impl FileSet {
+    /// Returns the number of stored paths.
     pub fn len(&self) -> usize {
         self.files.len()
     }
+
+    /// Get the id of the file corresponding to `path`.
+    ///
+    /// If either `path`'s [`anchor`](AnchoredPath::anchor) or the resolved path is not in
+    /// the set, returns [`None`].
     pub fn resolve_path(&self, path: AnchoredPath<'_>) -> Option<FileId> {
         let mut base = self.paths[&path.anchor].clone();
         base.pop();
@@ -26,19 +33,26 @@ impl FileSet {
         self.files.get(&path).copied()
     }
 
+    /// Get the id corresponding to `path` if it exists in the set.
     pub fn file_for_path(&self, path: &VfsPath) -> Option<&FileId> {
         self.files.get(path)
     }
 
+    /// Get the path corresponding to `file` if it exists in the set.
     pub fn path_for_file(&self, file: &FileId) -> Option<&VfsPath> {
         self.paths.get(file)
     }
 
+    /// Insert the `file_id, path` pair into the set.
+    ///
+    /// # Note
+    /// Multiple [`FileId`] can be mapped to the same [`VfsPath`], and vice-versa.
     pub fn insert(&mut self, file_id: FileId, path: VfsPath) {
         self.files.insert(path.clone(), file_id);
         self.paths.insert(file_id, path);
     }
 
+    /// Iterate over this set's ids.
     pub fn iter(&self) -> impl Iterator<Item = FileId> + '_ {
         self.paths.keys().copied()
     }
@@ -50,9 +64,31 @@ impl fmt::Debug for FileSet {
     }
 }
 
+/// This contains path prefixes to partition a [`Vfs`] into [`FileSet`]s.
+///
+/// # Example
+/// ```rust
+/// # use vfs::{file_set::FileSetConfigBuilder, VfsPath, Vfs};
+/// let mut builder = FileSetConfigBuilder::default();
+/// builder.add_file_set(vec![VfsPath::new_virtual_path("/src".to_string())]);
+/// let config = builder.build();
+/// let mut file_system = Vfs::default();
+/// file_system.set_file_contents(VfsPath::new_virtual_path("/src/main.rs".to_string()), Some(vec![]));
+/// file_system.set_file_contents(VfsPath::new_virtual_path("/src/lib.rs".to_string()), Some(vec![]));
+/// file_system.set_file_contents(VfsPath::new_virtual_path("/build.rs".to_string()), Some(vec![]));
+/// // contains the sets :
+/// // { "/src/main.rs", "/src/lib.rs" }
+/// // { "build.rs" }
+/// let sets = config.partition(&file_system);
+/// ```
 #[derive(Debug)]
 pub struct FileSetConfig {
+    /// Number of sets that `self` can partition a [`Vfs`] into.
+    ///
+    /// This should be the number of sets in `self.map` + 1 for files that don't fit in any
+    /// defined set.
     n_file_sets: usize,
+    /// Map from encoded paths to the set they belong to.
     map: fst::Map<Vec<u8>>,
 }
 
@@ -63,9 +99,14 @@ impl Default for FileSetConfig {
 }
 
 impl FileSetConfig {
+    /// Returns a builder for `FileSetConfig`.
     pub fn builder() -> FileSetConfigBuilder {
         FileSetConfigBuilder::default()
     }
+
+    /// Partition `vfs` into `FileSet`s.
+    ///
+    /// Creates a new [`FileSet`] for every set of prefixes in `self`.
     pub fn partition(&self, vfs: &Vfs) -> Vec<FileSet> {
         let mut scratch_space = Vec::new();
         let mut res = vec![FileSet::default(); self.len()];
@@ -75,9 +116,15 @@ impl FileSetConfig {
         }
         res
     }
+
+    /// Number of sets that `self` can partition a [`Vfs`] into.
     fn len(&self) -> usize {
         self.n_file_sets
     }
+
+    /// Returns the set index for the given `path`.
+    ///
+    /// `scratch_space` is used as a buffer and will be entirely replaced.
     fn classify(&self, path: &VfsPath, scratch_space: &mut Vec<u8>) -> usize {
         scratch_space.clear();
         path.encode(scratch_space);
@@ -91,6 +138,7 @@ impl FileSetConfig {
     }
 }
 
+/// Builder for [`FileSetConfig`].
 pub struct FileSetConfigBuilder {
     roots: Vec<Vec<VfsPath>>,
 }
@@ -102,12 +150,17 @@ impl Default for FileSetConfigBuilder {
 }
 
 impl FileSetConfigBuilder {
+    /// Returns the number of sets currently held.
     pub fn len(&self) -> usize {
         self.roots.len()
     }
+
+    /// Add a new set of paths prefixes.
     pub fn add_file_set(&mut self, roots: Vec<VfsPath>) {
         self.roots.push(roots)
     }
+
+    /// Build the `FileSetConfig`.
     pub fn build(self) -> FileSetConfig {
         let n_file_sets = self.roots.len() + 1;
         let map = {
@@ -127,11 +180,15 @@ impl FileSetConfigBuilder {
     }
 }
 
+/// Implements [`fst::Automaton`]
+///
+/// It will match if `prefix_of` is a prefix of the given data.
 struct PrefixOf<'a> {
     prefix_of: &'a [u8],
 }
 
 impl<'a> PrefixOf<'a> {
+    /// Creates a new `PrefixOf` from the given slice.
     fn new(prefix_of: &'a [u8]) -> Self {
         Self { prefix_of }
     }
diff --git a/crates/vfs/src/lib.rs b/crates/vfs/src/lib.rs
index 2b7b14524..e075d752b 100644
--- a/crates/vfs/src/lib.rs
+++ b/crates/vfs/src/lib.rs
@@ -53,9 +53,15 @@ pub use crate::{
 };
 pub use paths::{AbsPath, AbsPathBuf};
 
+/// Handle to a file in [`Vfs`]
+///
+/// Most functions in rust-analyzer use this when they need to refer to a file.
 #[derive(Copy, Clone, Debug, Ord, PartialOrd, Eq, PartialEq, Hash)]
 pub struct FileId(pub u32);
 
+/// Storage for all files read by rust-analyzer.
+///
+/// For more informations see the [crate-level](crate) documentation.
 #[derive(Default)]
 pub struct Vfs {
     interner: PathInterner,
@@ -63,40 +69,73 @@ pub struct Vfs {
     changes: Vec<ChangedFile>,
 }
 
+/// Changed file in the [`Vfs`].
 pub struct ChangedFile {
+    /// Id of the changed file
     pub file_id: FileId,
+    /// Kind of change
     pub change_kind: ChangeKind,
 }
 
 impl ChangedFile {
+    /// Returns `true` if the change is not [`Delete`](ChangeKind::Delete).
     pub fn exists(&self) -> bool {
         self.change_kind != ChangeKind::Delete
     }
+
+    /// Returns `true` if the change is [`Create`](ChangeKind::Create) or
+    /// [`Delete`](ChangeKind::Delete).
     pub fn is_created_or_deleted(&self) -> bool {
         matches!(self.change_kind, ChangeKind::Create | ChangeKind::Delete)
     }
 }
 
+/// Kind of [file change](ChangedFile).
 #[derive(Eq, PartialEq, Copy, Clone, Debug)]
 pub enum ChangeKind {
+    /// The file was (re-)created
     Create,
+    /// The file was modified
     Modify,
+    /// The file was deleted
     Delete,
 }
 
 impl Vfs {
+    /// Amount of files currently stored.
+    ///
+    /// Note that this includes deleted files.
     pub fn len(&self) -> usize {
         self.data.len()
     }
+
+    /// Id of the given path if it exists in the `Vfs` and is not deleted.
     pub fn file_id(&self, path: &VfsPath) -> Option<FileId> {
         self.interner.get(path).filter(|&it| self.get(it).is_some())
     }
+
+    /// File path corresponding to the given `file_id`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the id is not present in the `Vfs`.
     pub fn file_path(&self, file_id: FileId) -> VfsPath {
         self.interner.lookup(file_id).clone()
     }
+
+    /// File content corresponding to the given `file_id`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the id is not present in the `Vfs`, or if the corresponding file is
+    /// deleted.
     pub fn file_contents(&self, file_id: FileId) -> &[u8] {
         self.get(file_id).as_deref().unwrap()
     }
+
+    /// Returns an iterator over the stored ids and their corresponding paths.
+    ///
+    /// This will skip deleted files.
     pub fn iter(&self) -> impl Iterator<Item = (FileId, &VfsPath)> + '_ {
         (0..self.data.len())
             .map(|it| FileId(it as u32))
@@ -106,6 +145,13 @@ impl Vfs {
                 (file_id, path)
             })
     }
+
+    /// Update the `path` with the given `contents`. `None` means the file was deleted.
+    ///
+    /// Returns `true` if the file was modified, and saves the [change](ChangedFile).
+    ///
+    /// If the path does not currently exists in the `Vfs`, allocates a new
+    /// [`FileId`] for it.
     pub fn set_file_contents(&mut self, path: VfsPath, contents: Option<Vec<u8>>) -> bool {
         let file_id = self.alloc_file_id(path);
         let change_kind = match (&self.get(file_id), &contents) {
@@ -120,12 +166,24 @@ impl Vfs {
         self.changes.push(ChangedFile { file_id, change_kind });
         true
     }
+
+    /// Returns `true` if the `Vfs` contains [changes](ChangedFile).
     pub fn has_changes(&self) -> bool {
         !self.changes.is_empty()
     }
+
+    /// Drain and returns all the changes in the `Vfs`.
     pub fn take_changes(&mut self) -> Vec<ChangedFile> {
         mem::take(&mut self.changes)
     }
+
+    /// Returns the id associated with `path`
+    ///
+    /// - If `path` does not exists in the `Vfs`, allocate a new id for it, associated with a
+    /// deleted file;
+    /// - Else, returns `path`'s id.
+    ///
+    /// Does not record a change.
     fn alloc_file_id(&mut self, path: VfsPath) -> FileId {
         let file_id = self.interner.intern(path);
         let idx = file_id.0 as usize;
@@ -133,9 +191,21 @@ impl Vfs {
         self.data.resize_with(len, || None);
         file_id
     }
+
+    /// Returns the content associated with the given `file_id`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if no file is associated to that id.
     fn get(&self, file_id: FileId) -> &Option<Vec<u8>> {
         &self.data[file_id.0 as usize]
     }
+
+    /// Mutably returns the content associated with the given `file_id`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if no file is associated to that id.
     fn get_mut(&mut self, file_id: FileId) -> &mut Option<Vec<u8>> {
         &mut self.data[file_id.0 as usize]
     }
diff --git a/crates/vfs/src/loader.rs b/crates/vfs/src/loader.rs
index 40cf96020..d3bdae562 100644
--- a/crates/vfs/src/loader.rs
+++ b/crates/vfs/src/loader.rs
@@ -3,9 +3,12 @@ use std::fmt;
 
 use paths::{AbsPath, AbsPathBuf};
 
+/// A set of files on the file system.
 #[derive(Debug, Clone)]
 pub enum Entry {
+    /// The `Entry` is represented by a raw set of files.
     Files(Vec<AbsPathBuf>),
+    /// The `Entry` is represented by `Directories`.
     Directories(Directories),
 }
 
@@ -17,6 +20,8 @@ pub enum Entry {
 ///   * it is not under `exclude` path
 ///
 /// If many include/exclude paths match, the longest one wins.
+///
+/// If a path is in both `include` and `exclude`, the `exclude` one wins.
 #[derive(Debug, Clone, Default)]
 pub struct Directories {
     pub extensions: Vec<String>,
@@ -24,45 +29,99 @@ pub struct Directories {
     pub exclude: Vec<AbsPathBuf>,
 }
 
+/// [`Handle`]'s configuration.
 #[derive(Debug)]
 pub struct Config {
+    /// Set of initially loaded files.
     pub load: Vec<Entry>,
+    /// Index of watched entries in `load`.
+    ///
+    /// If a path in a watched entry is modified,the [`Handle`] should notify it.
     pub watch: Vec<usize>,
 }
 
+/// Message about an action taken by a [`Handle`].
 pub enum Message {
+    /// Indicate a gradual progress.
+    ///
+    /// This is supposed to be the number of loaded files.
     Progress { n_total: usize, n_done: usize },
+    /// The handle loaded the following files' content.
     Loaded { files: Vec<(AbsPathBuf, Option<Vec<u8>>)> },
 }
 
+/// Type that will receive [`Messages`](Message) from a [`Handle`].
 pub type Sender = Box<dyn Fn(Message) + Send>;
 
+/// Interface for reading and watching files.
 pub trait Handle: fmt::Debug {
+    /// Spawn a new handle with the given `sender`.
     fn spawn(sender: Sender) -> Self
     where
         Self: Sized;
+
+    /// Set this handle's configuration.
     fn set_config(&mut self, config: Config);
+
+    /// The file's content at `path` has been modified, and should be reloaded.
     fn invalidate(&mut self, path: AbsPathBuf);
+
+    /// Load the content of the given file, returning [`None`] if it does not
+    /// exists.
     fn load_sync(&mut self, path: &AbsPath) -> Option<Vec<u8>>;
 }
 
 impl Entry {
+    /// Returns:
+    /// ```text
+    /// Entry::Directories(Directories {
+    ///     extensions: ["rs"],
+    ///     include: [base],
+    ///     exclude: [base/.git],
+    /// })
+    /// ```
     pub fn rs_files_recursively(base: AbsPathBuf) -> Entry {
         Entry::Directories(dirs(base, &[".git"]))
     }
+
+    /// Returns:
+    /// ```text
+    /// Entry::Directories(Directories {
+    ///     extensions: ["rs"],
+    ///     include: [base],
+    ///     exclude: [base/.git, base/target],
+    /// })
+    /// ```
     pub fn local_cargo_package(base: AbsPathBuf) -> Entry {
         Entry::Directories(dirs(base, &[".git", "target"]))
     }
+
+    /// Returns:
+    /// ```text
+    /// Entry::Directories(Directories {
+    ///     extensions: ["rs"],
+    ///     include: [base],
+    ///     exclude: [base/.git, /tests, /examples, /benches],
+    /// })
+    /// ```
     pub fn cargo_package_dependency(base: AbsPathBuf) -> Entry {
         Entry::Directories(dirs(base, &[".git", "/tests", "/examples", "/benches"]))
     }
 
+    /// Returns `true` if `path` is included in `self`.
+    ///
+    /// See [`Directories::contains_file`].
     pub fn contains_file(&self, path: &AbsPath) -> bool {
         match self {
             Entry::Files(files) => files.iter().any(|it| it == path),
             Entry::Directories(dirs) => dirs.contains_file(path),
         }
     }
+
+    /// Returns `true` if `path` is included in `self`.
+    ///
+    /// - If `self` is `Entry::Files`, returns `false`
+    /// - Else, see [`Directories::contains_dir`].
     pub fn contains_dir(&self, path: &AbsPath) -> bool {
         match self {
             Entry::Files(_) => false,
@@ -72,6 +131,7 @@ impl Entry {
 }
 
 impl Directories {
+    /// Returns `true` if `path` is included in `self`.
     pub fn contains_file(&self, path: &AbsPath) -> bool {
         let ext = path.extension().unwrap_or_default();
         if self.extensions.iter().all(|it| it.as_str() != ext) {
@@ -79,9 +139,21 @@ impl Directories {
         }
         self.includes_path(path)
     }
+
+    /// Returns `true` if `path` is included in `self`.
+    ///
+    /// Since `path` is supposed to be a directory, this will not take extension
+    /// into account.
     pub fn contains_dir(&self, path: &AbsPath) -> bool {
         self.includes_path(path)
     }
+
+    /// Returns `true` if `path` is included in `self`.
+    ///
+    /// It is included if
+    ///   - An element in `self.include` is a prefix of `path`.
+    ///   - This path is longer than any element in `self.exclude` that is a prefix
+    ///     of `path`. In case of equality, exclusion wins.
     fn includes_path(&self, path: &AbsPath) -> bool {
         let mut include: Option<&AbsPathBuf> = None;
         for incl in &self.include {
@@ -105,6 +177,14 @@ impl Directories {
     }
 }
 
+/// Returns :
+/// ```text
+/// Directories {
+///     extensions: ["rs"],
+///     include: [base],
+///     exclude: [base/<exclude>],
+/// }
+/// ```
 fn dirs(base: AbsPathBuf, exclude: &[&str]) -> Directories {
     let exclude = exclude.iter().map(|it| base.join(it)).collect::<Vec<_>>();
     Directories { extensions: vec!["rs".to_string()], include: vec![base], exclude }
diff --git a/crates/vfs/src/path_interner.rs b/crates/vfs/src/path_interner.rs
index 4f70d61e8..2189e5e25 100644
--- a/crates/vfs/src/path_interner.rs
+++ b/crates/vfs/src/path_interner.rs
@@ -5,6 +5,7 @@ use rustc_hash::FxHashMap;
 
 use crate::{FileId, VfsPath};
 
+/// Structure to map between [`VfsPath`] and [`FileId`].
 #[derive(Default)]
 pub(crate) struct PathInterner {
     map: FxHashMap<VfsPath, FileId>,
@@ -12,9 +13,17 @@ pub(crate) struct PathInterner {
 }
 
 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(path).copied()
     }
+
+    /// 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 {
         if let Some(id) = self.get(&path) {
             return id;
@@ -25,6 +34,11 @@ impl PathInterner {
         id
     }
 
+    /// Returns the path corresponding to `id`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `id` does not exists in `self`.
     pub(crate) fn lookup(&self, id: FileId) -> &VfsPath {
         &self.vec[id.0 as usize]
     }
diff --git a/crates/vfs/src/vfs_path.rs b/crates/vfs/src/vfs_path.rs
index bd14911c9..2b3d7fd84 100644
--- a/crates/vfs/src/vfs_path.rs
+++ b/crates/vfs/src/vfs_path.rs
@@ -3,25 +3,37 @@ use std::fmt;
 
 use paths::{AbsPath, AbsPathBuf};
 
+/// Path in [`Vfs`].
+///
 /// Long-term, we want to support files which do not reside in the file-system,
-/// so we treat VfsPaths as opaque identifiers.
+/// so we treat `VfsPath`s as opaque identifiers.
+///
+/// [`Vfs`]: crate::Vfs
 #[derive(Clone, Ord, PartialOrd, Eq, PartialEq, Hash)]
 pub struct VfsPath(VfsPathRepr);
 
 impl VfsPath {
-    /// Creates an "in-memory" path from `/`-separates string.
+    /// Creates an "in-memory" path from `/`-separated string.
+    ///
     /// This is most useful for testing, to avoid windows/linux differences
+    ///
+    /// # Panics
+    ///
+    /// Panics if `path` does not start with `'/'`.
     pub fn new_virtual_path(path: String) -> VfsPath {
         assert!(path.starts_with('/'));
         VfsPath(VfsPathRepr::VirtualPath(VirtualPath(path)))
     }
 
+    /// Returns the `AbsPath` representation of `self` if `self` is on the file system.
     pub fn as_path(&self) -> Option<&AbsPath> {
         match &self.0 {
             VfsPathRepr::PathBuf(it) => Some(it.as_path()),
             VfsPathRepr::VirtualPath(_) => None,
         }
     }
+
+    /// Creates a new `VfsPath` with `path` adjoined to `self`.
     pub fn join(&self, path: &str) -> Option<VfsPath> {
         match &self.0 {
             VfsPathRepr::PathBuf(it) => {
@@ -34,12 +46,30 @@ impl VfsPath {
             }
         }
     }
+
+    /// Remove the last component of `self` if there is one.
+    ///
+    /// If `self` has no component, returns `false`; else returns `true`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use vfs::{AbsPathBuf, VfsPath};
+    /// let mut path = VfsPath::from(AbsPathBuf::assert("/foo/bar".into()));
+    /// assert!(path.pop());
+    /// assert_eq!(path, VfsPath::from(AbsPathBuf::assert("/foo".into())));
+    /// assert!(path.pop());
+    /// assert_eq!(path, VfsPath::from(AbsPathBuf::assert("/".into())));
+    /// assert!(!path.pop());
+    /// ```
     pub fn pop(&mut self) -> bool {
         match &mut self.0 {
             VfsPathRepr::PathBuf(it) => it.pop(),
             VfsPathRepr::VirtualPath(it) => it.pop(),
         }
     }
+
+    /// Returns `true` if `other` is a prefix of `self`.
     pub fn starts_with(&self, other: &VfsPath) -> bool {
         match (&self.0, &other.0) {
             (VfsPathRepr::PathBuf(lhs), VfsPathRepr::PathBuf(rhs)) => lhs.starts_with(rhs),
@@ -48,6 +78,10 @@ impl VfsPath {
             (VfsPathRepr::VirtualPath(_), _) => false,
         }
     }
+
+    /// Returns the `VfsPath` without its final component, if there is one.
+    ///
+    /// Returns [`None`] if the path is a root or prefix.
     pub fn parent(&self) -> Option<VfsPath> {
         let mut parent = self.clone();
         if parent.pop() {
@@ -57,6 +91,7 @@ impl VfsPath {
         }
     }
 
+    /// Returns `self`'s base name and file extension.
     pub fn name_and_extension(&self) -> Option<(&str, Option<&str>)> {
         match &self.0 {
             VfsPathRepr::PathBuf(p) => Some((
@@ -67,7 +102,14 @@ impl VfsPath {
         }
     }
 
-    // Don't make this `pub`
+    /// **Don't make this `pub`**
+    ///
+    /// Encode the path in the given buffer.
+    ///
+    /// The encoding will be `0` if [`AbsPathBuf`], `1` if [`VirtualPath`], followed
+    /// by `self`'s representation.
+    ///
+    /// Note that this encoding is dependent on the operating system.
     pub(crate) fn encode(&self, buf: &mut Vec<u8>) {
         let tag = match &self.0 {
             VfsPathRepr::PathBuf(_) => 0,
@@ -224,6 +266,7 @@ mod windows_paths {
     }
 }
 
+/// Internal, private representation of [`VfsPath`].
 #[derive(Clone, Ord, PartialOrd, Eq, PartialEq, Hash)]
 enum VfsPathRepr {
     PathBuf(AbsPathBuf),
@@ -260,13 +303,34 @@ impl fmt::Debug for VfsPathRepr {
     }
 }
 
+/// `/`-separated virtual path.
+///
+/// This is used to describe files that do not reside on the file system.
 #[derive(Debug, Clone, Ord, PartialOrd, Eq, PartialEq, Hash)]
 struct VirtualPath(String);
 
 impl VirtualPath {
+    /// Returns `true` if `other` is a prefix of `self` (as strings).
     fn starts_with(&self, other: &VirtualPath) -> bool {
         self.0.starts_with(&other.0)
     }
+
+    /// Remove the last component of `self`.
+    ///
+    /// This will find the last `'/'` in `self`, and remove everything after it,
+    /// including the `'/'`.
+    ///
+    /// If `self` contains no `'/'`, returns `false`; else returns `true`.
+    ///
+    /// # Example
+    ///
+    /// ```rust,ignore
+    /// let mut path = VirtualPath("/foo/bar".to_string());
+    /// path.pop();
+    /// assert_eq!(path.0, "/foo");
+    /// path.pop();
+    /// assert_eq!(path.0, "");
+    /// ```
     fn pop(&mut self) -> bool {
         let pos = match self.0.rfind('/') {
             Some(pos) => pos,
@@ -275,6 +339,17 @@ impl VirtualPath {
         self.0 = self.0[..pos].to_string();
         true
     }
+
+    /// Append the given *relative* path `path` to `self`.
+    ///
+    /// This will resolve any leading `"../"` in `path` before appending it.
+    ///
+    /// Returns [`None`] if `path` has more leading `"../"` than the number of
+    /// components in `self`.
+    ///
+    /// # Notes
+    ///
+    /// In practice, appending here means `self/path` as strings.
     fn join(&self, mut path: &str) -> Option<VirtualPath> {
         let mut res = self.clone();
         while path.starts_with("../") {
@@ -287,7 +362,18 @@ impl VirtualPath {
         Some(res)
     }
 
-    pub(crate) fn name_and_extension(&self) -> Option<(&str, Option<&str>)> {
+    /// Returns `self`'s base name and file extension.
+    ///
+    /// # Returns
+    /// - `None` if `self` ends with `"//"`.
+    /// - `Some((name, None))` if `self`'s base contains no `.`, or only one `.` at
+    /// the start.
+    /// - `Some((name, Some(extension))` else.
+    ///
+    /// # Note
+    /// The extension will not contains `.`. This means `"/foo/bar.baz.rs"` will
+    /// return `Some(("bar.baz", Some("rs"))`.
+    fn name_and_extension(&self) -> Option<(&str, Option<&str>)> {
         let file_path = if self.0.ends_with('/') { &self.0[..&self.0.len() - 1] } else { &self.0 };
         let file_name = match file_path.rfind('/') {
             Some(position) => &file_path[position + 1..],