1 files changed, 99 insertions, 0 deletions

diff --git a/crates/vfs/src/file_set.rs b/crates/vfs/src/file_set.rs
new file mode 100644
index 000000000..7dc721f7e
--- /dev/null
+++ b/crates/vfs/src/file_set.rs
@@ -0,0 +1,99 @@
+//! Partitions a list of files into disjoint subsets.
+//!
+//! Files which do not belong to any explicitly configured `FileSet` belong to
+//! the default `FileSet`.
+use std::{cmp, fmt, iter};
+
+use paths::AbsPathBuf;
+use rustc_hash::FxHashMap;
+
+use crate::{FileId, Vfs, VfsPath};
+
+#[derive(Default, Clone, Eq, PartialEq)]
+pub struct FileSet {
+    files: FxHashMap<VfsPath, FileId>,
+    paths: FxHashMap<FileId, VfsPath>,
+}
+
+impl FileSet {
+    pub fn resolve_path(&self, anchor: FileId, path: &str) -> Option<FileId> {
+        let mut base = self.paths[&anchor].clone();
+        base.pop();
+        let path = base.join(path);
+        let res = self.files.get(&path).copied();
+        res
+    }
+    pub fn insert(&mut self, file_id: FileId, path: VfsPath) {
+        self.files.insert(path.clone(), file_id);
+        self.paths.insert(file_id, path);
+    }
+    pub fn iter(&self) -> impl Iterator<Item = FileId> + '_ {
+        self.paths.keys().copied()
+    }
+}
+
+impl fmt::Debug for FileSet {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("FileSet").field("n_files", &self.files.len()).finish()
+    }
+}
+
+#[derive(Debug)]
+pub struct FileSetConfig {
+    n_file_sets: usize,
+    roots: Vec<(AbsPathBuf, usize)>,
+}
+
+impl FileSetConfig {
+    pub fn builder() -> FileSetConfigBuilder {
+        FileSetConfigBuilder::default()
+    }
+    pub fn partition(&self, vfs: &Vfs) -> Vec<FileSet> {
+        let mut res = vec![FileSet::default(); self.len()];
+        for (file_id, path) in vfs.iter() {
+            let root = self.classify(&path);
+            res[root].insert(file_id, path)
+        }
+        res
+    }
+    fn len(&self) -> usize {
+        self.n_file_sets
+    }
+    fn classify(&self, path: &VfsPath) -> usize {
+        for (root, idx) in self.roots.iter() {
+            if let Some(path) = path.as_path() {
+                if path.starts_with(root) {
+                    return *idx;
+                }
+            }
+        }
+        self.len() - 1
+    }
+}
+
+pub struct FileSetConfigBuilder {
+    roots: Vec<Vec<AbsPathBuf>>,
+}
+
+impl Default for FileSetConfigBuilder {
+    fn default() -> Self {
+        FileSetConfigBuilder { roots: Vec::new() }
+    }
+}
+
+impl FileSetConfigBuilder {
+    pub fn add_file_set(&mut self, roots: Vec<AbsPathBuf>) {
+        self.roots.push(roots)
+    }
+    pub fn build(self) -> FileSetConfig {
+        let n_file_sets = self.roots.len() + 1;
+        let mut roots: Vec<(AbsPathBuf, usize)> = self
+            .roots
+            .into_iter()
+            .enumerate()
+            .flat_map(|(i, paths)| paths.into_iter().zip(iter::repeat(i)))
+            .collect();
+        roots.sort_by_key(|(path, _)| cmp::Reverse(path.to_string_lossy().len()));
+        FileSetConfig { n_file_sets, roots }
+    }
+}