implement a blake3 content version layer for cache busting

works pretty much the same as our previous `?cache` parameter, but is implemented in a less ad-hoc way

crates/treehouse/Cargo.toml

@@ -15,6 +15,7 @@ chrono = "0.4.35"
 clap = { version = "4.3.22", features = ["derive"] }
 codespan-reporting = "0.11.1"
 copy_dir = "0.1.3"
+dashmap = "6.1.0"
 env_logger = "0.10.0"
 git2 = { version = "0.19.0", default-features = false, features = ["vendored-libgit2"] }
 handlebars = "4.3.7"

crates/treehouse/src/main.rs

@@ -9,7 +9,7 @@ use treehouse::cli::serve::serve;
 use treehouse::dirs::Dirs;
 use treehouse::generate::{self, Sources};
 use treehouse::vfs::asynch::AsyncDir;
-use treehouse::vfs::{AnchoredAtExt, DynDir, ToDynDir, VPathBuf};
+use treehouse::vfs::{AnchoredAtExt, Blake3ContentVersionCache, DynDir, ToDynDir, VPathBuf};
 use treehouse::vfs::{Cd, PhysicalDir};
 use treehouse::{
     cli::{
@@ -42,6 +42,8 @@ fn vfs_sources() -> anyhow::Result<DynDir> {
         PhysicalDir::new(PathBuf::from("content")).to_dyn(),
     );
 
+    let root = Blake3ContentVersionCache::new(root);
+
     Ok(root.to_dyn())
 }
 

crates/treehouse/src/vfs.rs

@@ -52,6 +52,7 @@ use std::{
 mod anchored;
 pub mod asynch;
 mod cd;
+mod content_version_cache;
 mod edit;
 mod empty;
 mod file;
@@ -62,6 +63,7 @@ mod physical;
 
 pub use anchored::*;
 pub use cd::*;
+pub use content_version_cache::*;
 pub use edit::*;
 pub use empty::*;
 pub use file::*;

crates/treehouse/src/vfs/content_version_cache.rs

@@ -0,0 +1,62 @@
+use std::fmt::{self, Debug};
+
+use dashmap::DashMap;
+use log::debug;
+
+use super::{Dir, DirEntry, EditPath, VPath, VPathBuf};
+
+pub struct Blake3ContentVersionCache<T> {
+    inner: T,
+    cache: DashMap<VPathBuf, Option<String>>,
+}
+
+impl<T> Blake3ContentVersionCache<T> {
+    pub fn new(inner: T) -> Self {
+        Self {
+            inner,
+            cache: DashMap::new(),
+        }
+    }
+}
+
+impl<T> Dir for Blake3ContentVersionCache<T>
+where
+    T: Dir,
+{
+    fn dir(&self, path: &VPath) -> Vec<DirEntry> {
+        self.inner.dir(path)
+    }
+
+    fn content(&self, path: &VPath) -> Option<Vec<u8>> {
+        self.inner.content(path)
+    }
+
+    fn content_version(&self, path: &VPath) -> Option<String> {
+        self.cache
+            .entry(path.to_owned())
+            .or_insert_with(|| {
+                self.content(path).map(|content| {
+                    let hash = blake3::hash(&content).to_hex();
+                    format!("b3-{}", &hash[0..8])
+                })
+            })
+            .clone()
+    }
+
+    fn anchor(&self, path: &VPath) -> Option<VPathBuf> {
+        self.inner.anchor(path)
+    }
+
+    fn edit_path(&self, path: &VPath) -> Option<EditPath> {
+        self.inner.edit_path(path)
+    }
+}
+
+impl<T> fmt::Debug for Blake3ContentVersionCache<T>
+where
+    T: Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Blake3ContentVersionCache({:?})", self.inner)
+    }
+}