remove treehouse-format crate and collapse everything into src

src/vfs/cd.rs

@@ -0,0 +1,54 @@
+use std::fmt;
+
+use super::{entries, Dir, Entries, Query, VPath, VPathBuf};
+
+pub struct Cd<T> {
+    parent: T,
+    path: VPathBuf,
+}
+
+impl<T> Cd<T> {
+    pub fn new(parent: T, path: VPathBuf) -> Self {
+        Self { parent, path }
+    }
+}
+
+impl<T> Cd<T>
+where
+    T: Dir,
+{
+    fn dir(&self, path: &VPath) -> Vec<VPathBuf> {
+        entries(&self.parent, &self.path.join(path))
+            .into_iter()
+            .map(|entry| {
+                entry
+                    .strip_prefix(&self.path)
+                    .expect("all entries must be anchored within `self.path`")
+                    .to_owned()
+            })
+            .collect()
+    }
+}
+
+impl<T> Dir for Cd<T>
+where
+    T: Dir,
+{
+    fn query(&self, path: &VPath, query: &mut Query) {
+        // The only query that meaningfully needs to return something else is `dir`, which must
+        // be modified to strip prefixes off of the parent's returned paths.
+        query.provide(|| Entries(self.dir(path)));
+
+        // Other queries can run unmodified, only passing them the right path.
+        self.parent.query(&self.path.join(path), query);
+    }
+}
+
+impl<T> fmt::Debug for Cd<T>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:?}/{:?}", self.parent, self.path)
+    }
+}