introduce the virtual filesystem everywhere

this unfortunately means I had to cut some features (bye bye commit history! for now)
stuff's not quite 100% working just yet (like branch links, which were and are still broken)
we also don't have content_version impls just yet

Cargo.lock

@@ -1545,20 +1545,6 @@ version = "0.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c20c8dbed6283a09604c3e69b4b7eeb54e298b8a600d4d5ecb5ad39de609f1d0"
 
-[[package]]
-name = "tower-livereload"
-version = "0.9.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "61d6cbbab4b2d3cafd21fb211cc4b06525a0df919c3e8ca3d36485b1c1bd4cd4"
-dependencies = [
- "bytes",
- "http",
- "http-body",
- "pin-project-lite",
- "tokio",
- "tower",
-]
-
 [[package]]
 name = "tower-service"
 version = "0.3.2"
@@ -1611,7 +1597,6 @@ dependencies = [
  "serde_json",
  "tokio",
  "toml_edit",
- "tower-livereload",
  "treehouse-format",
  "ulid",
  "url",

content/_treehouse/404.tree

@@ -1,10 +1,7 @@
 %% title = "404"
 
-% id = "404"
+% id = "01HMF8KQ997F1ZTEGDNAE2S6F1"
-- # 404
+- seems like the page you're looking for isn't here.
 
-    % id = "01HMF8KQ997F1ZTEGDNAE2S6F1"
+% id = "01HMF8KQ99XNMEP67NE3QH5698"
-    - seems like the page you're looking for isn't here.
+- care to go [back to the index][branch:treehouse]?
-
-    % id = "01HMF8KQ99XNMEP67NE3QH5698"
-    - care to go [back to the index][branch:treehouse]?

crates/treehouse/Cargo.toml

@@ -29,7 +29,6 @@ serde = { version = "1.0.183", features = ["derive"] }
 serde_json = "1.0.105"
 tokio = { version = "1.32.0", features = ["full"] }
 toml_edit = { version = "0.19.14", features = ["serde"] }
-tower-livereload = "0.9.2"
 walkdir = "2.3.3"
 ulid = "1.0.0"
 url = "2.5.0"

crates/treehouse/src/cli.rs

@@ -2,10 +2,10 @@ pub mod fix;
 pub mod serve;
 pub mod wc;
 
-use std::path::{Path, PathBuf};
-
 use clap::{Args, Parser, Subcommand};
 
+use crate::vfs::VPathBuf;
+
 #[derive(Parser)]
 pub struct ProgramArgs {
     #[clap(subcommand)]
@@ -41,20 +41,13 @@ pub enum Command {
 }
 
 #[derive(Args)]
-pub struct GenerateArgs {
+pub struct GenerateArgs {}
-    /// Only use commits as sources. This will cause the latest revision to be taken from the
-    /// Git history instead of the working tree.
-    ///
-    /// Recommended for deployment.
-    #[clap(long)]
-    pub commits_only: bool,
-}
 
 #[derive(Args)]
 pub struct FixArgs {
     /// Which file to fix. The fixed file will be printed into stdout so that you have a chance to
     /// see the changes.
-    pub file: PathBuf,
+    pub file: VPathBuf,
 
     /// If you're happy with the suggested changes, specifying this will apply them to the file
     /// (overwrite it in place.)
@@ -63,7 +56,7 @@ pub struct FixArgs {
 
     /// Write the previous version back to the specified path.
     #[clap(long)]
-    pub backup: Option<PathBuf>,
+    pub backup: Option<VPathBuf>,
 }
 
 #[derive(Args)]
@@ -85,17 +78,5 @@ pub struct ServeArgs {
 pub struct WcArgs {
     /// A list of paths to report the word counts of.
     /// If no paths are provided, the entire tree is word-counted.
-    pub paths: Vec<PathBuf>,
+    pub paths: Vec<VPathBuf>,
-}
-
-#[derive(Debug, Clone, Copy)]
-pub struct Paths<'a> {
-    pub target_dir: &'a Path,
-    pub template_target_dir: &'a Path,
-
-    pub static_dir: &'a Path,
-    pub template_dir: &'a Path,
-    pub content_dir: &'a Path,
-
-    pub config_file: &'a Path,
 }

crates/treehouse/src/cli/fix.rs

@@ -1,16 +1,17 @@
-use std::{ffi::OsStr, ops::Range};
+use std::ops::{ControlFlow, Range};
 
-use anyhow::Context;
+use anyhow::{anyhow, Context};
 use codespan_reporting::diagnostic::Diagnostic;
+use log::{error, info};
 use treehouse_format::ast::Branch;
-use walkdir::WalkDir;
 
 use crate::{
     parse::{self, parse_toml_with_diagnostics, parse_tree_with_diagnostics},
     state::{report_diagnostics, FileId, Source, Treehouse},
+    vfs::{self, Dir, Edit, VPath},
 };
 
-use super::{FixAllArgs, FixArgs, Paths};
+use super::{FixAllArgs, FixArgs};
 
 struct Fix {
     range: Range<usize>,
@@ -132,68 +133,102 @@ pub fn fix_file(
         })
 }
 
-pub fn fix_file_cli(fix_args: FixArgs) -> anyhow::Result<()> {
+pub fn fix_file_cli(fix_args: FixArgs, root: &dyn Dir) -> anyhow::Result<Edit> {
-    let utf8_filename = fix_args.file.to_string_lossy().into_owned();
+    let file = if &*fix_args.file == VPath::new("-") {
-    let file = if utf8_filename == "-" {
         std::io::read_to_string(std::io::stdin().lock()).context("cannot read file from stdin")?
     } else {
-        std::fs::read_to_string(&fix_args.file).context("cannot read file to fix")?
+        String::from_utf8(
+            root.content(&fix_args.file)
+                .ok_or_else(|| anyhow!("cannot read file to fix"))?,
+        )
+        .context("input file has invalid UTF-8")?
     };
 
     let mut treehouse = Treehouse::new();
     let mut diagnostics = vec![];
-    let file_id = treehouse.add_file(utf8_filename, Source::Other(file));
+    let file_id = treehouse.add_file(fix_args.file.as_str().to_owned(), Source::Other(file));
+    let edit_path = root.edit_path(&fix_args.file).ok_or_else(|| {
+        anyhow!(
+            "{} is not an editable file (perhaps it is not in a persistent path?)",
+            fix_args.file
+        )
+    })?;
 
+    Ok(
         if let Ok(fixed) = fix_file(&mut treehouse, &mut diagnostics, file_id) {
             if fix_args.apply {
                 // Try to write the backup first. If writing that fails, bail out without overwriting
                 // the source file.
                 if let Some(backup_path) = fix_args.backup {
-                std::fs::write(backup_path, treehouse.source(file_id).input())
+                    let backup_edit_path = root.edit_path(&backup_path).ok_or_else(|| {
-                    .context("cannot write backup; original file will not be overwritten")?;
+                        anyhow!("backup file {backup_path} is not an editable file")
+                    })?;
+                    Edit::Seq(vec![
+                        Edit::Write(
+                            backup_edit_path,
+                            treehouse.source(file_id).input().to_owned(),
+                        ),
+                        Edit::Write(edit_path, fixed),
+                    ])
+                } else {
+                    Edit::Write(edit_path, fixed)
                 }
-            std::fs::write(&fix_args.file, fixed).context("cannot overwrite original file")?;
             } else {
                 println!("{fixed}");
+                Edit::NoOp
             }
         } else {
             report_diagnostics(&treehouse.files, &diagnostics)?;
-    }
+            Edit::NoOp
-
+        },
-    Ok(())
+    )
 }
 
-pub fn fix_all_cli(fix_all_args: FixAllArgs, paths: &Paths<'_>) -> anyhow::Result<()> {
+pub fn fix_all_cli(fix_all_args: FixAllArgs, dir: &dyn Dir) -> anyhow::Result<Edit> {
-    for entry in WalkDir::new(paths.content_dir) {
+    let mut edits = vec![];
-        let entry = entry?;
+
-        if entry.file_type().is_file() && entry.path().extension() == Some(OsStr::new("tree")) {
+    fn fix_one(dir: &dyn Dir, path: &VPath) -> anyhow::Result<Edit> {
-            let file = std::fs::read_to_string(entry.path())
+        if path.extension() == Some("tree") {
-                .with_context(|| format!("cannot read file to fix: {:?}", entry.path()))?;
+            let Some(content) = dir.content(path) else {
-            let utf8_filename = entry.path().to_string_lossy();
+                return Ok(Edit::NoOp);
+            };
+            let content = String::from_utf8(content).context("file is not valid UTF-8")?;
 
             let mut treehouse = Treehouse::new();
             let mut diagnostics = vec![];
-            let file_id = treehouse.add_file(utf8_filename.into_owned(), Source::Other(file));
+            let file_id = treehouse.add_file(path.as_str().to_string(), Source::Other(content));
+            let edit_path = dir.edit_path(path).context("path is not editable")?;
 
             if let Ok(fixed) = fix_file(&mut treehouse, &mut diagnostics, file_id) {
                 if fixed != treehouse.source(file_id).input() {
-                    if fix_all_args.apply {
+                    return Ok(Edit::Write(edit_path, fixed));
-                        println!("fixing: {:?}", entry.path());
-                        std::fs::write(entry.path(), fixed).with_context(|| {
-                            format!("cannot overwrite original file: {:?}", entry.path())
-                        })?;
-                    } else {
-                        println!("will fix: {:?}", entry.path());
-                    }
                 }
             } else {
                 report_diagnostics(&treehouse.files, &diagnostics)?;
             }
         }
-    }
+
-    if !fix_all_args.apply {
+        Ok(Edit::NoOp)
-        println!("run with `--apply` to apply changes");
     }
 
-    Ok(())
+    info!("gathering edits");
+    vfs::walk_dir_rec(dir, VPath::ROOT, &mut |path| {
+        match fix_one(dir, path) {
+            Ok(Edit::NoOp) => (),
+            Ok(edit) => edits.push(edit),
+            Err(err) => error!("cannot fix {path}: {err:?}"),
+        }
+
+        ControlFlow::Continue(())
+    });
+
+    // NOTE: This number may be higher than you expect, because NoOp edits also count!
+    info!("{} edits to apply", edits.len());
+
+    if !fix_all_args.apply {
+        info!("dry run; add `--apply` to apply changes");
+        Ok(Edit::Dry(Box::new(Edit::All(edits))))
+    } else {
+        Ok(Edit::All(edits))
+    }
 }

crates/treehouse/src/cli/serve.rs

@@ -2,131 +2,78 @@
 mod live_reload;
 
 use std::fmt::Write;
-use std::{net::Ipv4Addr, path::PathBuf, sync::Arc};
+use std::{net::Ipv4Addr, sync::Arc};
 
-use anyhow::Context;
 use axum::{
     extract::{Path, Query, RawQuery, State},
     http::{
-        header::{CACHE_CONTROL, CONTENT_TYPE, LOCATION},
+        header::{CACHE_CONTROL, CONTENT_TYPE},
         HeaderValue, StatusCode,
     },
     response::{Html, IntoResponse, Response},
     routing::get,
     Router,
 };
-use log::{error, info};
+use log::info;
 use serde::Deserialize;
 use tokio::net::TcpListener;
 
-use crate::{
+use crate::generate::Sources;
-    config::Config,
+use crate::vfs::asynch::AsyncDir;
-    html::EscapeHtml,
+use crate::vfs::VPath;
-    state::{Source, Treehouse},
+use crate::{html::EscapeHtml, state::Source};
-};
 
-use super::Paths;
+mod system {
+    use crate::vfs::VPath;
 
-struct SystemPages {
+    pub const INDEX: &VPath = VPath::new_const("index");
-    index: String,
+    pub const FOUR_OH_FOUR: &VPath = VPath::new_const("_treehouse/404");
-    four_oh_four: String,
+    pub const B_DOCS: &VPath = VPath::new_const("_treehouse/b");
-    b_docs: String,
-    sandbox: String,
-
-    navmap: String,
 }
 
 struct Server {
-    config: Config,
+    sources: Arc<Sources>,
-    treehouse: Treehouse,
+    target: AsyncDir,
-    target_dir: PathBuf,
-    system_pages: SystemPages,
 }
 
-pub async fn serve(
+pub async fn serve(sources: Arc<Sources>, target: AsyncDir, port: u16) -> anyhow::Result<()> {
-    config: Config,
-    treehouse: Treehouse,
-    paths: &Paths<'_>,
-    port: u16,
-) -> anyhow::Result<()> {
     let app = Router::new()
-        .route("/", get(index))
+        .route("/", get(index)) // needed explicitly because * does not match empty paths
-        .route("/*page", get(page))
+        .route("/*path", get(vfs_entry))
         .route("/b", get(branch))
-        .route("/navmap.js", get(navmap))
-        .route("/sandbox", get(sandbox))
-        .route("/static/*file", get(static_file))
         .fallback(get(four_oh_four))
-        .with_state(Arc::new(Server {
+        .with_state(Arc::new(Server { sources, target }));
-            config,
-            treehouse,
-            target_dir: paths.target_dir.to_owned(),
-            system_pages: SystemPages {
-                index: std::fs::read_to_string(paths.target_dir.join("index.html"))
-                    .context("cannot read index page")?,
-                four_oh_four: std::fs::read_to_string(paths.target_dir.join("_treehouse/404.html"))
-                    .context("cannot read 404 page")?,
-                b_docs: std::fs::read_to_string(paths.target_dir.join("_treehouse/b.html"))
-                    .context("cannot read /b documentation page")?,
-                sandbox: std::fs::read_to_string(paths.target_dir.join("static/html/sandbox.html"))
-                    .context("cannot read sandbox page")?,
-                navmap: std::fs::read_to_string(paths.target_dir.join("navmap.js"))
-                    .context("cannot read navigation map")?,
-            },
-        }));
 
     #[cfg(debug_assertions)]
-    let app = live_reload::live_reload(app);
+    let app = app.nest("/dev/live-reload", live_reload::router());
 
     info!("serving on port {port}");
     let listener = TcpListener::bind((Ipv4Addr::from([0u8, 0, 0, 0]), port)).await?;
     Ok(axum::serve(listener, app).await?)
 }
 
-fn get_content_type(path: &str) -> Option<&'static str> {
+fn get_content_type(extension: &str) -> Option<&'static str> {
-    match () {
+    match extension {
-        _ if path.ends_with(".html") => Some("text/html"),
+        "html" => Some("text/html"),
-        _ if path.ends_with(".js") => Some("text/javascript"),
+        "js" => Some("text/javascript"),
-        _ if path.ends_with(".woff2") => Some("font/woff2"),
+        "woff" => Some("font/woff2"),
-        _ if path.ends_with(".svg") => Some("image/svg+xml"),
+        "svg" => Some("image/svg+xml"),
         _ => None,
     }
 }
 
-async fn index(State(state): State<Arc<Server>>) -> Response {
-    Html(state.system_pages.index.clone()).into_response()
-}
-
-async fn navmap(State(state): State<Arc<Server>>) -> Response {
-    let mut response = state.system_pages.navmap.clone().into_response();
-    response
-        .headers_mut()
-        .insert(CONTENT_TYPE, HeaderValue::from_static("text/javascript"));
-    response
-}
-
-async fn four_oh_four(State(state): State<Arc<Server>>) -> Response {
-    (
-        StatusCode::NOT_FOUND,
-        Html(state.system_pages.four_oh_four.clone()),
-    )
-        .into_response()
-}
-
 #[derive(Deserialize)]
-struct StaticFileQuery {
+struct VfsQuery {
-    cache: Option<String>,
+    #[serde(rename = "v")]
+    content_version: Option<String>,
 }
 
-async fn static_file(
+async fn get_static_file(path: &str, query: &VfsQuery, state: &Server) -> Option<Response> {
-    Path(path): Path<String>,
+    let vpath = VPath::try_new(path).ok()?;
-    Query(query): Query<StaticFileQuery>,
+    let content = state.target.content(vpath).await?;
-    State(state): State<Arc<Server>>,
+    let mut response = content.into_response();
-) -> Response {
-    if let Ok(file) = tokio::fs::read(state.target_dir.join("static").join(&path)).await {
-        let mut response = file.into_response();
 
-        if let Some(content_type) = get_content_type(&path) {
+    if let Some(content_type) = vpath.extension().and_then(get_content_type) {
         response
             .headers_mut()
             .insert(CONTENT_TYPE, HeaderValue::from_static(content_type));
@@ -134,77 +81,80 @@ async fn static_file(
         response.headers_mut().remove(CONTENT_TYPE);
     }
 
-        if query.cache.is_some() {
+    if query.content_version.is_some() {
         response.headers_mut().insert(
             CACHE_CONTROL,
             HeaderValue::from_static("public, max-age=31536000, immutable"),
         );
     }
 
+    Some(response)
+}
+
+async fn vfs_entry(
+    Path(path): Path<String>,
+    Query(query): Query<VfsQuery>,
+    State(state): State<Arc<Server>>,
+) -> Response {
+    if let Some(response) = get_static_file(&path, &query, &state).await {
         response
     } else {
         four_oh_four(State(state)).await
     }
 }
 
-async fn page(Path(path): Path<String>, State(state): State<Arc<Server>>) -> Response {
+async fn system_page(target: &AsyncDir, path: &VPath) -> Response {
-    let bare_path = path.strip_suffix(".html").unwrap_or(&path);
+    if let Some(content) = target.content(path).await {
-    if let Some(redirected_path) = state.config.redirects.page.get(bare_path) {
+        (StatusCode::NOT_FOUND, Html(content)).into_response()
-        return (
+    } else {
-            StatusCode::MOVED_PERMANENTLY,
+        (
-            [(LOCATION, format!("{}/{redirected_path}", state.config.site))],
+            StatusCode::INTERNAL_SERVER_ERROR,
+            format!("500 Internal Server Error: system page {path} is not available"),
         )
-            .into_response();
+            .into_response()
-    }
-
-    let html_path = format!("{bare_path}.html");
-    if let Ok(file) = tokio::fs::read(state.target_dir.join(&*html_path)).await {
-        ([(CONTENT_TYPE, "text/html")], file).into_response()
-    } else {
-        four_oh_four(State(state)).await
     }
 }
 
-async fn sandbox(State(state): State<Arc<Server>>) -> Response {
+async fn index(State(state): State<Arc<Server>>) -> Response {
-    // Small hack to prevent the LiveReloadLayer from injecting itself into the sandbox.
+    system_page(&state.target, system::INDEX).await
-    // The sandbox is always nested under a different page, so there's no need to do that.
-    let mut response = Html(state.system_pages.sandbox.clone()).into_response();
-    #[cfg(debug_assertions)]
-    {
-        response
-            .extensions_mut()
-            .insert(live_reload::DisableLiveReload);
-    }
-    // Debounce requests a bit. There's a tendency to have very many sandboxes on a page, and
-    // loading this page as many times as there are sandboxes doesn't seem like the best way to do
-    // things.
-    response
-        .headers_mut()
-        .insert(CACHE_CONTROL, HeaderValue::from_static("max-age=10"));
-    response
 }
 
-async fn branch(RawQuery(named_id): RawQuery, State(state): State<Arc<Server>>) -> Html<String> {
+async fn four_oh_four(State(state): State<Arc<Server>>) -> Response {
+    system_page(&state.target, system::FOUR_OH_FOUR).await
+}
+
+async fn branch(RawQuery(named_id): RawQuery, State(state): State<Arc<Server>>) -> Response {
     if let Some(named_id) = named_id {
         let branch_id = state
+            .sources
             .treehouse
             .branches_by_named_id
             .get(&named_id)
             .copied()
-            .or_else(|| state.treehouse.branch_redirects.get(&named_id).copied());
+            .or_else(|| {
+                state
+                    .sources
+                    .treehouse
+                    .branch_redirects
+                    .get(&named_id)
+                    .copied()
+            });
         if let Some(branch_id) = branch_id {
-            let branch = state.treehouse.tree.branch(branch_id);
+            let branch = state.sources.treehouse.tree.branch(branch_id);
             if let Source::Tree {
                 input, target_path, ..
-            } = state.treehouse.source(branch.file_id)
+            } = state.sources.treehouse.source(branch.file_id)
             {
-                match std::fs::read_to_string(target_path) {
+                if let Some(content) = state
-                    Ok(content) => {
+                    .target
-                        let branch_markdown_content = input[branch.content.clone()].trim();
+                    .content(target_path)
+                    .await
+                    .and_then(|s| String::from_utf8(s).ok())
+                {
+                    let branch_markup = input[branch.content.clone()].trim();
                     let mut per_page_metadata =
                         String::from("<meta property=\"og:description\" content=\"");
-                        write!(per_page_metadata, "{}", EscapeHtml(branch_markdown_content))
+                    write!(per_page_metadata, "{}", EscapeHtml(branch_markup)).unwrap();
-                            .unwrap();
                     per_page_metadata.push_str("\">");
 
                     const PER_PAGE_METADATA_REPLACEMENT_STRING: &str = "<!-- treehouse-ca37057a-cff5-45b3-8415-3b02dbf6c799-per-branch-metadata -->";
@@ -213,17 +163,20 @@ async fn branch(RawQuery(named_id): RawQuery, State(state): State<Arc<Server>>)
                         &per_page_metadata,
                         // Replace one under the assumption that it appears in all pages.
                         1,
-                        ));
+                    ))
-                    }
+                    .into_response();
-                    Err(e) => {
+                } else {
-                        error!("error while reading file {target_path:?}: {e:?}");
+                    return (
-                    }
+                        StatusCode::INTERNAL_SERVER_ERROR,
+                        format!("500 Internal Server Error: branch metadata points to entry {target_path} which does not have readable content")
+                    )
+                        .into_response();
                 }
             }
         }
 
-        Html(state.system_pages.four_oh_four.clone())
+        system_page(&state.target, system::FOUR_OH_FOUR).await
     } else {
-        Html(state.system_pages.b_docs.clone())
+        system_page(&state.target, system::B_DOCS).await
     }
 }

crates/treehouse/src/cli/serve/live_reload.rs

@@ -1,21 +1,28 @@
-use axum::{
+use std::time::Duration;
-    http::{header::CONTENT_TYPE, Response},
-    Router,
-};
 
-#[derive(Debug, Clone, Copy)]
+use axum::{routing::get, Router};
-pub struct DisableLiveReload;
+use tokio::time::sleep;
 
-pub fn live_reload(router: Router) -> Router {
+pub fn router<S>() -> Router<S> {
-    router.layer(tower_livereload::LiveReloadLayer::new().response_predicate(
+    let router = Router::new().route("/back-up", get(back_up));
-        |response: &Response<_>| {
+
-            let is_html = response
+    // The endpoint for immediate reload is only enabled on debug builds.
-                .headers()
+    // Release builds use the exponential backoff system that detects is the WebSocket is closed.
-                .get(CONTENT_TYPE)
+    #[cfg(debug_assertions)]
-                .and_then(|v| v.to_str().ok())
+    let router = router.route("/stall", get(stall));
-                .is_some_and(|v| v.starts_with("text/html"));
+
-            let is_disabled = response.extensions().get::<DisableLiveReload>().is_some();
+    router.with_state(())
-            is_html && !is_disabled
+}
-        },
+
-    ))
+#[cfg(debug_assertions)]
+async fn stall() -> String {
+    loop {
+        // Sleep for a day, I guess. Just to uphold the connection forever without really using any
+        // significant resources.
+        sleep(Duration::from_secs(60 * 60 * 24)).await;
+    }
+}
+
+async fn back_up() -> String {
+    "".into()
 }

crates/treehouse/src/cli/wc.rs

@@ -1,12 +1,11 @@
-use std::{ffi::OsStr, path::Path};
+use std::ops::ControlFlow;
 
-use anyhow::Context;
 use treehouse_format::ast::{Branch, Roots};
-use walkdir::WalkDir;
 
 use crate::{
     parse::parse_tree_with_diagnostics,
     state::{report_diagnostics, Source, Treehouse},
+    vfs::{self, Dir, VPath},
 };
 
 use super::WcArgs;
@@ -29,14 +28,14 @@ fn wc_roots(source: &str, roots: &Roots) -> usize {
         .sum()
 }
 
-pub fn wc_cli(content_dir: &Path, mut wc_args: WcArgs) -> anyhow::Result<()> {
+pub fn wc_cli(content_dir: &dyn Dir, mut wc_args: WcArgs) -> anyhow::Result<()> {
     if wc_args.paths.is_empty() {
-        for entry in WalkDir::new(content_dir) {
+        vfs::walk_dir_rec(content_dir, VPath::ROOT, &mut |path| {
-            let entry = entry?;
+            if path.extension() == Some("tree") {
-            if entry.file_type().is_file() && entry.path().extension() == Some(OsStr::new("tree")) {
+                wc_args.paths.push(path.to_owned());
-                wc_args.paths.push(entry.into_path());
-            }
             }
+            ControlFlow::Continue(())
+        });
     }
 
     let mut treehouse = Treehouse::new();
@@ -44,15 +43,11 @@ pub fn wc_cli(content_dir: &Path, mut wc_args: WcArgs) -> anyhow::Result<()> {
     let mut total = 0;
 
     for path in &wc_args.paths {
-        let file = std::fs::read_to_string(path)
+        if let Some(content) = content_dir
-            .with_context(|| format!("cannot read file to word count: {path:?}"))?;
+            .content(path)
-        let path_without_ext = path.with_extension("");
+            .and_then(|b| String::from_utf8(b).ok())
-        let utf8_filename = path_without_ext
+        {
-            .strip_prefix(content_dir)
+            let file_id = treehouse.add_file(path.to_string(), Source::Other(content));
-            .expect("paths should be rooted within the content directory")
-            .to_string_lossy();
-
-        let file_id = treehouse.add_file(utf8_filename.into_owned(), Source::Other(file));
             match parse_tree_with_diagnostics(&mut treehouse, file_id) {
                 Ok(parsed) => {
                     let source = treehouse.source(file_id);
@@ -65,6 +60,7 @@ pub fn wc_cli(content_dir: &Path, mut wc_args: WcArgs) -> anyhow::Result<()> {
                 }
             }
         }
+    }
 
     println!("{total:>8} total");
 

crates/treehouse/src/config.rs

@@ -1,11 +1,8 @@
-use std::{
+use std::{collections::HashMap, ops::ControlFlow};
-    collections::HashMap, ffi::OsStr, fs::File, io::BufReader, ops::ControlFlow, path::Path,
-};
 
-use anyhow::Context;
+use anyhow::{anyhow, Context};
-use log::debug;
+use log::{debug, error};
 use serde::{Deserialize, Serialize};
-use walkdir::WalkDir;
 
 use crate::{
     html::highlight::{
@@ -13,7 +10,7 @@ use crate::{
         Syntax,
     },
     import_map::ImportRoot,
-    vfs::{self, ReadFilesystem, VPath, VPathBuf},
+    vfs::{self, Dir, VPath, VPathBuf},
 };
 
 #[derive(Debug, Clone, Deserialize, Serialize)]
@@ -102,8 +99,8 @@ pub enum Markup {
 }
 
 impl Config {
-    pub fn autopopulate_emoji(&mut self, dir: &dyn ReadFilesystem) -> anyhow::Result<()> {
+    pub fn autopopulate_emoji(&mut self, dir: &dyn Dir) -> anyhow::Result<()> {
-        vfs::walk_rec(dir, VPath::ROOT, &mut |path| {
+        vfs::walk_dir_rec(dir, VPath::ROOT, &mut |path| {
             if path.extension().is_some_and(is_emoji_file) {
                 if let Some(emoji_name) = path.file_stem() {
                     if !self.emoji.contains_key(emoji_name) {
@@ -118,8 +115,8 @@ impl Config {
         Ok(())
     }
 
-    pub fn autopopulate_pics(&mut self, dir: &dyn ReadFilesystem) -> anyhow::Result<()> {
+    pub fn autopopulate_pics(&mut self, dir: &dyn Dir) -> anyhow::Result<()> {
-        vfs::walk_rec(dir, VPath::ROOT, &mut |path| {
+        vfs::walk_dir_rec(dir, VPath::ROOT, &mut |path| {
             if path.extension().is_some_and(is_pic_file) {
                 if let Some(pic_name) = path.file_stem() {
                     let pic_id = pic_name
@@ -142,38 +139,48 @@ impl Config {
         format!("{}/{}", self.site, page)
     }
 
-    pub fn pic_url(&self, pics_fs: &dyn ReadFilesystem, id: &str) -> String {
+    pub fn pic_url(&self, pics_dir: &dyn Dir, id: &str) -> String {
         vfs::url(
             &self.site,
-            pics_fs,
+            pics_dir,
             self.pics
                 .get(id)
                 .map(|x| &**x)
                 .unwrap_or(VPath::new("404.png")),
         )
+        .expect("pics_dir is not anchored anywhere")
     }
 
     /// Loads all syntax definition files.
-    pub fn load_syntaxes(&mut self, dir: &Path) -> anyhow::Result<()> {
+    pub fn load_syntaxes(&mut self, dir: &dyn Dir) -> anyhow::Result<()> {
-        for entry in WalkDir::new(dir) {
+        vfs::walk_dir_rec(dir, VPath::ROOT, &mut |path| {
-            let entry = entry?;
+            if path.extension() == Some("json") {
-            if entry.path().extension() == Some(OsStr::new("json")) {
+                let name = path
-                let name = entry
-                    .path()
                     .file_stem()
-                    .expect("syntax file name should have a stem")
+                    .expect("syntax file name should have a stem due to the .json extension");
-                    .to_string_lossy();
                 debug!("loading syntax {name:?}");
 
-                let syntax: Syntax = serde_json::from_reader(BufReader::new(
+                let result: Result<Syntax, _> = dir
-                    File::open(entry.path()).context("could not open syntax file")?,
+                    .content(path)
-                ))
+                    .ok_or_else(|| anyhow!("syntax .json is not a file"))
-                .context("could not deserialize syntax file")?;
+                    .and_then(|b| {
+                        String::from_utf8(b).context("syntax .json contains invalid UTF-8")
+                    })
+                    .and_then(|s| {
+                        serde_json::from_str(&s).context("could not deserialize syntax file")
+                    });
+                match result {
+                    Ok(syntax) => {
                         let compiled = compile_syntax(&syntax);
-                self.syntaxes.insert(name.into_owned(), compiled);
+                        self.syntaxes.insert(name.to_owned(), compiled);
+                    }
+                    Err(err) => error!("error while loading syntax file `{path}`: {err}"),
                 }
             }
 
+            ControlFlow::Continue(())
+        });
+
         Ok(())
     }
 }

crates/treehouse/src/dirs.rs

@@ -0,0 +1,15 @@
+use crate::vfs::DynDir;
+
+#[derive(Debug, Clone)]
+pub struct Dirs {
+    pub root: DynDir,
+
+    pub content: DynDir,
+    pub static_: DynDir,
+    pub template: DynDir,
+
+    // `static` directories
+    pub pics: DynDir,
+    pub emoji: DynDir,
+    pub syntax: DynDir,
+}

crates/treehouse/src/generate.rs

@@ -1,103 +1,53 @@
-use std::{
+mod dir_helper;
-    collections::HashMap,
+mod include_static_helper;
-    ffi::OsStr,
-    path::{Path, PathBuf},
-    time::Instant,
-};
 
-use anyhow::{anyhow, bail, Context};
+use std::{collections::HashMap, fmt, ops::ControlFlow, sync::Arc};
-use codespan_reporting::{
+
-    diagnostic::{Diagnostic, Label, LabelStyle, Severity},
+use anyhow::{anyhow, ensure, Context};
-    files::Files as _,
+use codespan_reporting::diagnostic::Diagnostic;
-};
+use dir_helper::DirHelper;
-use copy_dir::copy_dir;
 use handlebars::{handlebars_helper, Handlebars};
+use include_static_helper::IncludeStaticHelper;
 use log::{debug, error, info};
 use serde::Serialize;
-use walkdir::WalkDir;
 
 use crate::{
-    cli::Paths,
     config::Config,
+    dirs::Dirs,
     fun::seasons::Season,
-    history::History,
+    html::{breadcrumbs::breadcrumbs_to_html, navmap::NavigationMap, tree::branches_to_html},
-    html::{
-        breadcrumbs::breadcrumbs_to_html,
-        navmap::{build_navigation_map, NavigationMap},
-        tree::branches_to_html,
-    },
     import_map::ImportMap,
-    include_static::IncludeStatic,
     parse::parse_tree_with_diagnostics,
-    state::{has_errors, report_diagnostics, RevisionInfo, Source},
+    state::{report_diagnostics, Source},
-    static_urls::StaticUrls,
     tree::SemaRoots,
-    vfs::{CdExt, ReadFilesystem, VPath, VPathBuf},
+    vfs::{self, Cd, Dir, DirEntry, DynDir, MemDir, Overlay, ToDynDir, VPath, VPathBuf},
 };
 
 use crate::state::{FileId, Treehouse};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum LatestRevision {
-    /// The working tree is treated as the latest revision.
-    WorkingTree,
-    /// The latest commit is treated as the latest revision. The working tree is ignored.
-    LatestCommit,
-}
-
-struct Generator {
-    tree_files: Vec<PathBuf>,
-    git: git2::Repository,
-    history: History,
-    latest_revision: LatestRevision,
-}
-
 #[derive(Debug, Clone)]
-struct ParsedTree {
+pub struct ParsedTree {
-    source_path: String,
     root_key: String,
     tree_path: String,
     file_id: FileId,
-    target_path: PathBuf,
+    target_path: VPathBuf,
 }
 
 #[derive(Serialize)]
-pub struct Page {
+struct Page {
-    pub title: String,
+    title: String,
-    pub thumbnail: Option<Thumbnail>,
+    thumbnail: Option<Thumbnail>,
-    pub scripts: Vec<String>,
+    scripts: Vec<String>,
-    pub styles: Vec<String>,
+    styles: Vec<String>,
-    pub breadcrumbs: String,
+    breadcrumbs: String,
-    pub tree_path: Option<String>,
+    tree_path: Option<String>,
-    pub tree: String,
+    tree: String,
-
-    pub revision: RevisionInfo,
-    pub revision_url: String,
-    pub source_url: String,
-    pub history_url: String,
 }
 
 #[derive(Serialize)]
-pub struct Commit {
+struct Thumbnail {
-    pub revision_number: usize,
+    url: String,
-    pub hash: String,
+    alt: Option<String>,
-    pub hash_short: String,
-    pub summary: String,
-    pub body: String,
-}
-
-#[derive(Serialize)]
-pub struct HistoryPage {
-    pub title: String,
-    pub commits: Vec<Commit>,
-    pub tree_path: String,
-    pub is_history: bool, // always true
-}
-
-#[derive(Serialize)]
-pub struct Thumbnail {
-    pub url: String,
-    pub alt: Option<String>,
 }
 
 #[derive(Serialize)]
@@ -114,138 +64,61 @@ struct PageTemplateData<'a> {
     page: Page,
 }
 
-#[derive(Serialize)]
+fn create_handlebars(site: &str, static_: DynDir) -> Handlebars<'static> {
-struct HistoryTemplateData<'a> {
+    let mut handlebars = Handlebars::new();
-    #[serde(flatten)]
-    base: &'a BaseTemplateData<'a>,
-    page: HistoryPage,
-}
 
-impl Generator {
-    fn add_directory_rec(&mut self, directory: &Path) -> anyhow::Result<()> {
-        for entry in WalkDir::new(directory) {
-            let entry = entry?;
-            if entry.path().extension() == Some(OsStr::new("tree")) {
-                self.tree_files.push(entry.path().to_owned());
-            }
-        }
-        Ok(())
-    }
-
-    fn init_handlebars(handlebars: &mut Handlebars<'_>, paths: &Paths<'_>, config: &Config) {
     handlebars_helper!(cat: |a: String, b: String| a + &b);
 
     handlebars.register_helper("cat", Box::new(cat));
-        handlebars.register_helper(
+    handlebars.register_helper("asset", Box::new(DirHelper::new(site, static_.clone())));
-            "asset",
-            Box::new(StaticUrls::new(
-                paths.target_dir.join("static"),
-                format!("{}/static", config.site),
-            )),
-        );
     handlebars.register_helper(
         "include_static",
-            Box::new(IncludeStatic {
+        Box::new(IncludeStaticHelper::new(static_)),
-                // NOTE: Again, allow referring to generated static assets.
-                // This is necessary for import maps, for whom the <src> attribute is not
-                // currently supported.
-                base_dir: paths.target_dir.join("static"),
-            }),
     );
-    }
 
-    fn register_template(
+    handlebars
-        handlebars: &mut Handlebars<'_>,
+}
-        treehouse: &mut Treehouse,
-        diagnostics: &mut Vec<Diagnostic<FileId>>,
-        name: &str,
-        path: &Path,
-    ) -> anyhow::Result<FileId> {
-        let source = std::fs::read_to_string(path)
-            .with_context(|| format!("cannot read template file {path:?}"))?;
-        let file_id =
-            treehouse.add_file(path.to_string_lossy().into_owned(), Source::Other(source));
-        let source = treehouse.source(file_id);
-        if let Err(error) = handlebars.register_template_string(name, source) {
-            Self::wrangle_handlebars_error_into_diagnostic(
-                treehouse,
-                diagnostics,
-                file_id,
-                error.line_no,
-                error.column_no,
-                error.reason().to_string(),
-            )?;
-        }
-        Ok(file_id)
-    }
 
-    fn wrangle_handlebars_error_into_diagnostic(
+fn load_templates(handlebars: &mut Handlebars, dir: &dyn Dir) {
-        treehouse: &mut Treehouse,
+    vfs::walk_dir_rec(dir, VPath::ROOT, &mut |path| {
-        diagnostics: &mut Vec<Diagnostic<FileId>>,
+        if path.extension() == Some("hbs") {
-        file_id: FileId,
+            if let Some(content) = dir.content(path).and_then(|b| String::from_utf8(b).ok()) {
-        line: Option<usize>,
+                if let Err(err) = handlebars.register_template_string(path.as_str(), content) {
-        column: Option<usize>,
+                    error!("in template: {err}");
-        message: String,
-    ) -> anyhow::Result<()> {
-        if let (Some(line), Some(column)) = (line, column) {
-            let line_range = treehouse
-                .files
-                .line_range(file_id, line)
-                .expect("file was added to the list");
-            diagnostics.push(Diagnostic {
-                severity: Severity::Error,
-                code: Some("template".into()),
-                message,
-                labels: vec![Label {
-                    style: LabelStyle::Primary,
-                    file_id,
-                    range: line_range.start + column..line_range.start + column + 1,
-                    message: String::new(),
-                }],
-                notes: vec![],
-            })
-        } else {
-            let file = treehouse.filename(file_id);
-            bail!("template error in {file}: {message}");
                 }
-        Ok(())
             }
+        }
+        ControlFlow::Continue(())
+    });
+}
 
-    fn parse_tree(
+fn parse_tree(
     treehouse: &mut Treehouse,
     config: &Config,
     source: String,
-        source_path: String,
+    source_path: VPathBuf,
+    target_path: VPathBuf,
     tree_path: String,
-        target_path: PathBuf,
+) -> anyhow::Result<(Option<ParsedTree>, Vec<Diagnostic<FileId>>)> {
-        revision: RevisionInfo,
-    ) -> anyhow::Result<(Option<ParsedTree>, Vec<Diagnostic<FileId>>)> {
     let file_id = treehouse.add_file(
-            format!("{source_path}@{}", revision.commit_short),
+        source_path.as_str().to_owned(),
         Source::Tree {
             input: source,
             target_path: target_path.clone(),
             tree_path: tree_path.clone(),
-                revision_info: revision.clone(),
         },
     );
 
     match parse_tree_with_diagnostics(treehouse, file_id) {
         Ok(roots) => {
             let mut diagnostics = vec![];
-                let roots =
+            let roots = SemaRoots::from_roots(treehouse, &mut diagnostics, config, file_id, roots);
-                    SemaRoots::from_roots(treehouse, &mut diagnostics, config, file_id, roots);
 
-                let root_key = if revision.is_latest {
+            let root_key = tree_path.clone();
-                    tree_path.clone()
-                } else {
-                    format!("{tree_path}@{}", revision.number)
-                };
             treehouse.roots.insert(root_key.clone(), roots);
 
             Ok((
                 Some(ParsedTree {
-                        source_path,
                     root_key,
                     tree_path,
                     file_id,
@@ -256,236 +129,117 @@ impl Generator {
         }
         Err(diagnostics) => Ok((None, diagnostics)),
     }
-    }
+}
 
-    fn parse_trees(
+fn parse_trees(
-        &self,
     config: &Config,
-        paths: &Paths<'_>,
+    dirs: &Dirs,
-    ) -> anyhow::Result<(Treehouse, Vec<ParsedTree>, Vec<Diagnostic<FileId>>)> {
+) -> anyhow::Result<(Treehouse, HashMap<VPathBuf, ParsedTree>)> {
     let mut treehouse = Treehouse::new();
     let mut diagnostics = vec![];
-        let mut parsed_trees = vec![];
+    let mut parsed_trees = HashMap::new();
 
-        for path in &self.tree_files {
+    vfs::walk_dir_rec(&*dirs.content, VPath::ROOT, &mut |path| {
-            let utf8_path = path.to_string_lossy();
+        if path.extension() == Some("tree") {
+            if let Some(source) = dirs
+                .content
+                .content(path)
+                .and_then(|b| String::from_utf8(b).ok())
+            {
+                let tree_path = path.with_extension("");
+                let target_path = path.with_extension("html");
 
-            let tree_path = path
+                debug!("tree file: {path}");
-                .strip_prefix(paths.content_dir)
-                .unwrap_or(path)
-                .with_extension("")
-                .to_string_lossy()
-                .replace('\\', "/");
-            debug!("tree file: {path:?}");
 
-            let page_history = self.history.by_page.get(&utf8_path[..]);
+                match parse_tree(
-            let working_revision_number = page_history
-                .map(|history| history.revisions.len() + 1)
-                .unwrap_or(1);
-
-            if self.latest_revision == LatestRevision::WorkingTree {
-                let source = std::fs::read_to_string(path)?;
-                let target_path = paths.target_dir.join(&tree_path).with_extension("html");
-                let (parsed_tree, mut parse_diagnostics) = Self::parse_tree(
                     &mut treehouse,
                     config,
                     source,
-                    utf8_path.clone().into_owned(),
+                    path.to_owned(),
-                    tree_path.clone(),
                     target_path,
-                    RevisionInfo {
+                    tree_path.as_str().to_owned(),
-                        is_latest: true,
+                ) {
-                        number: working_revision_number,
+                    Ok((parsed_tree, mut parse_diagnostics)) => {
-                        commit: "working".into(),
-                        commit_short: "working".into(),
-                    },
-                )?;
                         diagnostics.append(&mut parse_diagnostics);
                         if let Some(parsed_tree) = parsed_tree {
-                    parsed_trees.push(parsed_tree);
+                            parsed_trees.insert(tree_path, parsed_tree);
+                        }
+                    }
+                    Err(err) => {
+                        error!("failed to parse tree {path}: {err:?}")
+                    }
+                }
             }
         }
 
-            if let Some(page_history) = page_history {
+        ControlFlow::Continue(())
-                for (i, revision) in page_history.revisions.iter().enumerate() {
+    });
-                    let revision_number = page_history.revisions.len() - i;
 
-                    let source = String::from_utf8(
+    report_diagnostics(&treehouse.files, &diagnostics)?;
-                        self.git.find_blob(revision.blob_oid)?.content().to_owned(),
-                    )?;
 
-                    let target_path = paths
+    Ok((treehouse, parsed_trees))
-                        .target_dir
+}
-                        .join(format!("{tree_path}@{revision_number}"))
-                        .with_extension("html");
 
-                    let (parsed_tree, parse_diagnostics) = Self::parse_tree(
+// TODO: Generation of pages in static/html
-                        &mut treehouse,
+//
-                        config,
+// for (name, &file_id) in &template_file_ids {
-                        source,
+//     let filename = name.rsplit_once('/').unwrap_or(("", name)).1;
-                        utf8_path.clone().into_owned(),
+//     if !filename.starts_with('_') {
-                        tree_path.clone(),
+//         let templated_html = match handlebars.render(name, &base_template_data) {
-                        target_path,
+//             Ok(html) => html,
-                        RevisionInfo {
+//             Err(error) => {
-                            is_latest: false,
+//                 Self::wrangle_handlebars_error_into_diagnostic(
-                            number: revision_number,
+//                     treehouse,
-                            commit: revision.commit_oid.to_string(),
+//                     &mut global_diagnostics,
-                            commit_short: revision.commit_short(),
+//                     file_id,
-                        },
+//                     error.line_no,
-                    )?;
+//                     error.column_no,
-                    _ = parse_diagnostics; // We don't reemit diagnostics from old revisions.
+//                     error.desc,
-                    if let Some(parsed_tree) = parsed_tree {
+//                 )?;
-                        // If this commit is also considered to be the latest revision, we need
+//                 continue;
-                        // to generate a second version of the page that will act as the
+//             }
-                        // latest one.
+//         };
-                        let is_latest =
+//         std::fs::write(
-                            self.latest_revision == LatestRevision::LatestCommit && i == 0;
+//             paths.template_target_dir.join(name).with_extension("html"),
-                        if is_latest {
+//             templated_html,
-                            let root_key = parsed_tree.tree_path.clone();
+//         )?;
-                            treehouse.roots.insert(
+//     }
-                                root_key.clone(),
+// }
-                                treehouse.roots.get(&parsed_tree.root_key).unwrap().clone(),
+
+fn generate_tree(
+    sources: &Sources,
+    dirs: &Dirs,
+    handlebars: &Handlebars,
+    parsed_tree: &ParsedTree,
+) -> anyhow::Result<String> {
+    let breadcrumbs = breadcrumbs_to_html(
+        &sources.config,
+        &sources.navigation_map,
+        &parsed_tree.root_key,
     );
 
-                            let target_path =
-                                paths.target_dir.join(&tree_path).with_extension("html");
-                            let file_id = {
-                                let file = treehouse.files.get(parsed_tree.file_id).unwrap();
-                                let filename = file.name().clone();
-                                let Source::Tree {
-                                    input,
-                                    tree_path,
-                                    target_path,
-                                    revision_info,
-                                } = file.source().clone()
-                                else {
-                                    panic!(".tree files must have Tree sources")
-                                };
-                                treehouse.add_file(
-                                    filename,
-                                    Source::Tree {
-                                        input,
-                                        tree_path,
-                                        target_path: target_path.clone(),
-                                        revision_info: RevisionInfo {
-                                            is_latest: true,
-                                            ..revision_info
-                                        },
-                                    },
-                                )
-                            };
-
-                            parsed_trees.push(ParsedTree {
-                                root_key,
-                                target_path,
-                                file_id,
-                                ..parsed_tree.clone()
-                            })
-                        }
-
-                        parsed_trees.push(parsed_tree);
-                    }
-                }
-            }
-        }
-
-        Ok((treehouse, parsed_trees, diagnostics))
-    }
-
-    fn generate_all_files(
-        &self,
-        treehouse: &mut Treehouse,
-        config: &Config,
-        paths: &Paths<'_>,
-        root_fs: &dyn ReadFilesystem,
-        navigation_map: &NavigationMap,
-        parsed_trees: Vec<ParsedTree>,
-    ) -> anyhow::Result<Vec<Diagnostic<FileId>>> {
-        let mut global_diagnostics = vec![];
-
-        let mut handlebars: Handlebars<'static> = Handlebars::new();
-        Self::init_handlebars(&mut handlebars, paths, config);
-
-        let mut template_file_ids = HashMap::new();
-        for entry in WalkDir::new(paths.template_dir) {
-            let entry = entry.context("cannot read directory entry")?;
-            let path = entry.path();
-            if !entry.file_type().is_dir() && path.extension() == Some(OsStr::new("hbs")) {
-                let relative_path = path
-                    .strip_prefix(paths.template_dir)?
-                    .to_string_lossy()
-                    .into_owned()
-                    .replace('\\', "/");
-                let file_id = Self::register_template(
-                    &mut handlebars,
-                    treehouse,
-                    &mut global_diagnostics,
-                    &relative_path,
-                    path,
-                )?;
-                template_file_ids.insert(relative_path, file_id);
-            }
-        }
-
-        let import_map =
-            ImportMap::generate(config.site.clone(), &config.build.javascript.import_roots);
-
-        let base_template_data = BaseTemplateData {
-            config,
-            import_map: serde_json::to_string_pretty(&import_map)
-                .expect("import map should be serializable to JSON"),
-            season: Season::current(),
-        };
-
-        std::fs::create_dir_all(paths.template_target_dir)?;
-        for (name, &file_id) in &template_file_ids {
-            let filename = name.rsplit_once('/').unwrap_or(("", name)).1;
-            if !filename.starts_with('_') {
-                let templated_html = match handlebars.render(name, &base_template_data) {
-                    Ok(html) => html,
-                    Err(error) => {
-                        Self::wrangle_handlebars_error_into_diagnostic(
-                            treehouse,
-                            &mut global_diagnostics,
-                            file_id,
-                            error.line_no,
-                            error.column_no,
-                            error.desc,
-                        )?;
-                        continue;
-                    }
-                };
-                std::fs::write(
-                    paths.template_target_dir.join(name).with_extension("html"),
-                    templated_html,
-                )?;
-            }
-        }
-
-        for parsed_tree in parsed_trees {
-            debug!("generating: {:?}", parsed_tree.target_path);
-
-            let breadcrumbs = breadcrumbs_to_html(config, navigation_map, &parsed_tree.root_key);
-
     let mut tree = String::new();
-            // Temporarily steal the tree out of the treehouse.
+    let roots = sources
-            let roots = treehouse
+        .treehouse
         .roots
-                .remove(&parsed_tree.root_key)
+        .get(&parsed_tree.root_key)
         .expect("tree should have been added to the treehouse");
     branches_to_html(
         &mut tree,
-                treehouse,
+        &sources.treehouse,
-                config,
+        &sources.config,
-                root_fs,
+        dirs,
-                paths,
         parsed_tree.file_id,
         &roots.branches,
     );
 
-            let revision = treehouse
+    let base_template_data = BaseTemplateData {
-                .revision_info(parsed_tree.file_id)
+        config: &sources.config,
-                .expect(".tree files should have Tree sources");
+        import_map: serde_json::to_string_pretty(&sources.import_map)
+            .expect("import map should be serializable to JSON"),
+        season: Season::current(),
+    };
+
     let template_data = PageTemplateData {
         base: &base_template_data,
         page: Page {
@@ -495,223 +249,203 @@ impl Generator {
                 .thumbnail
                 .as_ref()
                 .map(|thumbnail| Thumbnail {
-                            url: config
+                    url: sources.config.pic_url(&*dirs.pics, &thumbnail.id),
-                                .pic_url(&root_fs.cd(VPathBuf::new("static/pics")), &thumbnail.id),
                     alt: thumbnail.alt.clone(),
                 }),
             scripts: roots.attributes.scripts.clone(),
             styles: roots.attributes.styles.clone(),
             breadcrumbs,
-                    tree_path: treehouse
+            tree_path: sources
+                .treehouse
                 .tree_path(parsed_tree.file_id)
                 .map(|s| s.to_owned()),
             tree,
-
-                    revision_url: format!("{}/{}", config.site, parsed_tree.root_key),
-                    source_url: format!(
-                        "{}/{}/{}",
-                        config.commit_base_url, revision.commit, parsed_tree.source_path,
-                    ),
-                    history_url: format!("{}/h/{}", config.site, parsed_tree.tree_path),
-                    revision: revision.clone(),
         },
     };
-            let mut template_name = roots
+    let template_name = roots
         .attributes
         .template
         .clone()
         .unwrap_or_else(|| "_tree.hbs".into());
 
-            if !template_file_ids.contains_key(&template_name) {
+    ensure!(
-                template_name = "_tree.hbs".into();
+        handlebars.has_template(&template_name),
-            }
+        "template {template_name} does not exist"
+    );
 
-            // Reinsert the stolen roots.
+    handlebars
-            treehouse.roots.insert(parsed_tree.root_key, roots);
+        .render(&template_name, &template_data)
+        .context("template rendering failed")
+}
 
-            let templated_html = match handlebars.render(&template_name, &template_data) {
+fn generate_tree_or_error(
+    sources: &Sources,
+    dirs: &Dirs,
+    handlebars: &Handlebars,
+    parsed_tree: &ParsedTree,
+) -> String {
+    match generate_tree(sources, dirs, handlebars, parsed_tree) {
         Ok(html) => html,
-                Err(error) => {
+        Err(error) => format!("error: {error:?}"),
-                    Self::wrangle_handlebars_error_into_diagnostic(
-                        treehouse,
-                        // TODO: This should dump diagnostics out somewhere else.
-                        &mut global_diagnostics,
-                        template_file_ids[&template_name],
-                        error.line_no,
-                        error.column_no,
-                        error.desc,
-                    )?;
-                    continue;
-                }
-            };
-
-            std::fs::create_dir_all(
-                parsed_tree
-                    .target_path
-                    .parent()
-                    .expect("there should be a parent directory to generate files into"),
-            )?;
-            std::fs::write(parsed_tree.target_path, templated_html)?;
-        }
-
-        for (path, page_history) in &self.history.by_page {
-            let tree_path = path
-                .strip_prefix("content/")
-                .unwrap_or(path)
-                .strip_suffix(".tree")
-                .unwrap_or(path);
-            let target_path = paths
-                .target_dir
-                .join("h")
-                .join(path.strip_prefix("content/").unwrap_or(path))
-                .with_extension("html");
-            std::fs::create_dir_all(target_path.parent().unwrap())?;
-
-            let template_data = HistoryTemplateData {
-                base: &base_template_data,
-                page: HistoryPage {
-                    title: format!("page history: {tree_path}"),
-                    commits: page_history
-                        .revisions
-                        .iter()
-                        .enumerate()
-                        .map(|(i, revision)| Commit {
-                            revision_number: page_history.revisions.len() - i,
-                            hash: revision.commit_oid.to_string(),
-                            hash_short: revision.commit_short(),
-                            summary: self
-                                .history
-                                .commits
-                                .get(&revision.commit_oid)
-                                .map(|c| c.summary.as_str())
-                                .unwrap_or("<no summary available>")
-                                .to_owned(),
-                            body: self
-                                .history
-                                .commits
-                                .get(&revision.commit_oid)
-                                .map(|c| c.body.as_str())
-                                .unwrap_or("<no body available>")
-                                .to_owned(),
-                        })
-                        .collect(),
-                    tree_path: tree_path.to_owned(),
-                    is_history: true,
-                },
-            };
-            let templated_html = match handlebars.render("_history.hbs", &template_data) {
-                Ok(html) => html,
-                Err(error) => {
-                    Self::wrangle_handlebars_error_into_diagnostic(
-                        treehouse,
-                        // TODO: This should dump diagnostics out somewhere else.
-                        &mut global_diagnostics,
-                        template_file_ids["_history.hbs"],
-                        error.line_no,
-                        error.column_no,
-                        error.desc,
-                    )?;
-                    continue;
-                }
-            };
-
-            std::fs::write(target_path, templated_html)?;
-        }
-
-        Ok(global_diagnostics)
     }
 }
 
-pub fn generate(
+pub struct Sources {
-    paths: &Paths<'_>,
+    pub config: Config,
-    src: &dyn ReadFilesystem,
+    pub treehouse: Treehouse,
-    latest_revision: LatestRevision,
+    pub parsed_trees: HashMap<VPathBuf, ParsedTree>,
-) -> anyhow::Result<(Config, Treehouse)> {
+    pub navigation_map: NavigationMap,
-    let start = Instant::now();
+    pub import_map: ImportMap,
+}
 
+impl Sources {
+    pub fn load(dirs: &Dirs) -> anyhow::Result<Self> {
         info!("loading config");
         let mut config: Config = toml_edit::de::from_str(
-        &src.content(VPath::new("treehouse.toml"))
+            &dirs
+                .root
+                .content(VPath::new("treehouse.toml"))
                 .map(String::from_utf8)
                 .ok_or_else(|| anyhow!("config file does not exist"))??,
         )
         .context("failed to deserialize config")?;
         config.site = std::env::var("TREEHOUSE_SITE").unwrap_or(config.site);
-    config.autopopulate_emoji(&src.cd(VPathBuf::new("static/emoji")))?;
+        config.autopopulate_emoji(&*dirs.emoji)?;
-    config.autopopulate_pics(&src.cd(VPathBuf::new("static/pic")))?;
+        config.autopopulate_pics(&*dirs.pics)?;
-    config.load_syntaxes(&paths.static_dir.join("syntax"))?;
+        config.load_syntaxes(&*dirs.syntax)?;
 
-    // TODO: WriteFilesystem, such that we can write into the target directory?
+        info!("parsing tree files");
+        let (treehouse, parsed_trees) = parse_trees(&config, dirs)?;
 
-    info!("cleaning target directory");
+        info!("constructing navigation map");
-    let _ = std::fs::remove_dir_all(paths.target_dir);
+        let navigation_map = NavigationMap::build(&treehouse, "index");
-    std::fs::create_dir_all(paths.target_dir)?;
 
-    info!("copying static directory to target directory");
+        info!("constructing import map");
-    copy_dir(paths.static_dir, paths.target_dir.join("static"))?;
+        let import_map = ImportMap::generate(
+            &config.site,
+            &Cd::new(dirs.static_.clone(), VPathBuf::new("js")),
+            &config.build.javascript.import_roots,
+        );
 
-    info!("getting history");
+        Ok(Sources {
-    let git = git2::Repository::open(".")?;
+            config,
-    let history = History::get(&git)?;
+            treehouse,
-
-    info!("parsing tree");
-    let mut generator = Generator {
-        tree_files: vec![],
-        git,
-        history,
-        latest_revision,
-    };
-    generator.add_directory_rec(paths.content_dir)?;
-    let (mut treehouse, parsed_trees, diagnostics) = generator.parse_trees(&config, paths)?;
-    report_diagnostics(&treehouse.files, &diagnostics)?;
-    if has_errors(&diagnostics) {
-        bail!("diagnostics emitted during parsing");
-    }
-
-    // NOTE: The navigation map is a legacy feature that is lazy-loaded when fragment-based
-    // navigation is used.
-    // I couldn't be bothered with adding it to the import map since fragment-based navigation is
-    // only used on very old links. Adding caching to the navigation map is probably not worth it.
-    info!("generating navigation map");
-    let navigation_map = build_navigation_map(&treehouse, "index");
-    std::fs::write(
-        paths.target_dir.join("navmap.js"),
-        navigation_map.to_javascript(),
-    )?;
-
-    info!("generating standalone pages");
-    let diagnostics = generator.generate_all_files(
-        &mut treehouse,
-        &config,
-        paths,
-        src,
-        &navigation_map,
             parsed_trees,
-    )?;
+            navigation_map,
-    report_diagnostics(&treehouse.files, &diagnostics)?;
+            import_map,
+        })
+    }
+}
 
-    info!("generating change history pages");
+/// Acceleration structure for `dir` operations on [`TreehouseDir`]s.
+#[derive(Debug, Default)]
+struct DirIndex {
+    full_path: VPathBuf,
+    children: HashMap<VPathBuf, DirIndex>,
+}
 
-    let duration = start.elapsed();
+impl DirIndex {
-    info!("generation done in {duration:?}");
+    pub fn new<'a>(paths: impl Iterator<Item = &'a VPath>) -> Self {
+        let mut root = DirIndex::default();
 
-    if !has_errors(&diagnostics) {
+        for path in paths {
-        Ok((config, treehouse))
+            let mut parent = &mut root;
+            let mut full_path = VPath::ROOT.to_owned();
+            for segment in path.segments() {
+                full_path.push(segment);
+                let child = parent
+                    .children
+                    .entry(segment.to_owned())
+                    .or_insert_with(|| DirIndex {
+                        full_path: full_path.clone(),
+                        children: HashMap::new(),
+                    });
+                parent = child;
+            }
+        }
+
+        root
+    }
+}
+
+struct TreehouseDir {
+    dirs: Arc<Dirs>,
+    sources: Arc<Sources>,
+    dir_index: DirIndex,
+    handlebars: Handlebars<'static>,
+}
+
+impl TreehouseDir {
+    fn new(dirs: Arc<Dirs>, sources: Arc<Sources>, dir_index: DirIndex) -> Self {
+        let mut handlebars = create_handlebars(&sources.config.site, dirs.static_.clone());
+        load_templates(&mut handlebars, &dirs.template);
+
+        Self {
+            dirs,
+            sources,
+            dir_index,
+            handlebars,
+        }
+    }
+}
+
+impl Dir for TreehouseDir {
+    fn dir(&self, path: &VPath) -> Vec<DirEntry> {
+        let mut index = &self.dir_index;
+        for component in path.segments() {
+            if let Some(child) = index.children.get(component) {
+                index = child;
             } else {
-        bail!("generation errors occurred; diagnostics were emitted with detailed descriptions");
+                // There cannot possibly be any entries under an invalid path.
+                // Bail early.
+                return vec![];
+            }
+        }
+
+        index
+            .children
+            .values()
+            .map(|child| DirEntry {
+                path: child.full_path.clone(),
+            })
+            .collect()
+    }
+
+    fn content(&self, path: &VPath) -> Option<Vec<u8>> {
+        debug!("content({path})");
+
+        let path = if path.is_root() {
+            VPath::new_const("index")
+        } else {
+            path
+        };
+        let mut path = path.to_owned();
+        if path.extension() == Some("html") {
+            path.set_extension("");
+        }
+
+        self.sources.parsed_trees.get(&path).map(|parsed_tree| {
+            generate_tree_or_error(&self.sources, &self.dirs, &self.handlebars, parsed_tree).into()
+        })
+    }
+
+    fn content_version(&self, _path: &VPath) -> Option<String> {
+        None
     }
 }
 
-pub fn regenerate_or_report_error(
+impl fmt::Debug for TreehouseDir {
-    paths: &Paths<'_>,
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-    src: &dyn ReadFilesystem,
+        f.write_str("TreehouseDir")
-    latest_revision: LatestRevision,
-) -> anyhow::Result<(Config, Treehouse)> {
-    info!("regenerating site content");
-
-    let result = generate(paths, src, latest_revision);
-    if let Err(e) = &result {
-        error!("{e:?}");
     }
-    result
+}
+
+pub fn target(dirs: Arc<Dirs>, sources: Arc<Sources>) -> DynDir {
+    let mut root = MemDir::new();
+    root.add(VPath::new("static"), dirs.static_.clone());
+
+    let dir_index = DirIndex::new(sources.parsed_trees.keys().map(|x| &**x));
+    let tree_view = TreehouseDir::new(dirs, sources, dir_index);
+
+    Overlay::new(tree_view.to_dyn(), root.to_dyn()).to_dyn()
 }

crates/treehouse/src/generate/dir_helper.rs

@@ -0,0 +1,37 @@
+use handlebars::{Context, Handlebars, Helper, HelperDef, RenderContext, RenderError, ScopedJson};
+use serde_json::Value;
+
+use crate::vfs::{self, DynDir, VPath};
+
+pub struct DirHelper {
+    site: String,
+    dir: DynDir,
+}
+
+impl DirHelper {
+    pub fn new(site: &str, dir: DynDir) -> Self {
+        Self {
+            site: site.to_owned(),
+            dir,
+        }
+    }
+}
+
+impl HelperDef for DirHelper {
+    fn call_inner<'reg: 'rc, 'rc>(
+        &self,
+        h: &Helper<'reg, 'rc>,
+        _: &'reg Handlebars<'reg>,
+        _: &'rc Context,
+        _: &mut RenderContext<'reg, 'rc>,
+    ) -> Result<ScopedJson<'reg, 'rc>, RenderError> {
+        if let Some(path) = h.param(0).and_then(|v| v.value().as_str()) {
+            let vpath = VPath::try_new(path).map_err(|e| RenderError::new(e.to_string()))?;
+            let url = vfs::url(&self.site, &self.dir, vpath)
+                .ok_or_else(|| RenderError::new("path is not anchored anywhere"))?;
+            Ok(ScopedJson::Derived(Value::String(url)))
+        } else {
+            Err(RenderError::new("missing path string"))
+        }
+    }
+}

crates/treehouse/src/generate/include_static_helper.rs

@@ -0,0 +1,37 @@
+use handlebars::{Context, Handlebars, Helper, HelperDef, RenderContext, RenderError, ScopedJson};
+use serde_json::Value;
+
+use crate::vfs::{DynDir, VPath};
+
+pub struct IncludeStaticHelper {
+    dir: DynDir,
+}
+
+impl IncludeStaticHelper {
+    pub fn new(dir: DynDir) -> Self {
+        Self { dir }
+    }
+}
+
+impl HelperDef for IncludeStaticHelper {
+    fn call_inner<'reg: 'rc, 'rc>(
+        &self,
+        h: &Helper<'reg, 'rc>,
+        _: &'reg Handlebars<'reg>,
+        _: &'rc Context,
+        _: &mut RenderContext<'reg, 'rc>,
+    ) -> Result<ScopedJson<'reg, 'rc>, RenderError> {
+        if let Some(path) = h.param(0).and_then(|v| v.value().as_str()) {
+            let vpath = VPath::try_new(path).map_err(|e| RenderError::new(e.to_string()))?;
+            let url = String::from_utf8(
+                self.dir
+                    .content(vpath)
+                    .ok_or_else(|| RenderError::new("file does not exist"))?,
+            )
+            .map_err(|_| RenderError::new("included file does not contain UTF-8 text"))?;
+            Ok(ScopedJson::Derived(Value::String(url)))
+        } else {
+            Err(RenderError::new("missing path string"))
+        }
+    }
+}

crates/treehouse/src/html/djot.rs

@@ -17,10 +17,10 @@ use jotdown::OrderedListNumbering::*;
 use jotdown::SpanLinkType;
 
 use crate::config::Config;
+use crate::dirs::Dirs;
 use crate::state::FileId;
 use crate::state::Treehouse;
 use crate::vfs;
-use crate::vfs::ReadFilesystem;
 
 use super::highlight::highlight;
 
@@ -28,10 +28,9 @@ use super::highlight::highlight;
 pub struct Renderer<'a> {
     pub config: &'a Config,
 
-    pub emoji_fs: &'a dyn ReadFilesystem,
+    pub dirs: &'a Dirs,
-    pub pics_fs: &'a dyn ReadFilesystem,
 
-    pub treehouse: &'a mut Treehouse,
+    pub treehouse: &'a Treehouse,
     pub file_id: FileId,
     pub page_id: String,
 }
@@ -376,7 +375,7 @@ impl<'a> Writer<'a> {
                                 let pic_url = self
                                     .renderer
                                     .config
-                                    .pic_url(self.renderer.pics_fs, placeholder_pic_id);
+                                    .pic_url(&*self.renderer.dirs.pics, placeholder_pic_id);
                                 write_attr(&pic_url, out);
                                 out.push('"');
 
@@ -563,7 +562,12 @@ impl<'a> Writer<'a> {
                         out.push_str(r#"">"#)
                     }
 
-                    let url = vfs::url(&self.renderer.config.site, self.renderer.emoji_fs, vpath);
+                    let url = vfs::url(
+                        &self.renderer.config.site,
+                        &*self.renderer.dirs.emoji,
+                        vpath,
+                    )
+                    .expect("emoji directory is not anchored anywhere");
 
                     // TODO: this could do with better alt text
                     write!(
@@ -644,7 +648,7 @@ impl<'a> Writer<'a> {
                     )
                 }),
             "page" => Some(config.page_url(linked)),
-            "pic" => Some(config.pic_url(self.renderer.pics_fs, linked)),
+            "pic" => Some(config.pic_url(&*self.renderer.dirs.pics, linked)),
             _ => None,
         })
     }

crates/treehouse/src/html/navmap.rs

@@ -1,50 +1,39 @@
 use std::collections::HashMap;
 
-use serde::Serialize;
-
 use crate::{
     state::Treehouse,
     tree::{attributes::Content, SemaBranchId},
 };
 
-#[derive(Debug, Clone, Default, Serialize)]
+#[derive(Debug, Clone, Default)]
+struct NavigationMapBuilder {
+    stack: Vec<String>,
+    navigation_map: NavigationMap,
+}
+
+impl NavigationMapBuilder {
+    fn enter_tree(&mut self, tree: String) {
+        self.stack.push(tree.clone());
+        self.navigation_map.paths.insert(tree, self.stack.clone());
+    }
+
+    fn exit_tree(&mut self) {
+        self.stack.pop();
+    }
+
+    fn finish(self) -> NavigationMap {
+        self.navigation_map
+    }
+}
+
+#[derive(Debug, Clone, Default)]
 pub struct NavigationMap {
     /// Tells you which pages need to be opened to get to the key.
     pub paths: HashMap<String, Vec<String>>,
 }
 
 impl NavigationMap {
-    pub fn to_javascript(&self) -> String {
+    pub fn build(treehouse: &Treehouse, root_tree_path: &str) -> Self {
-        format!(
-            "export const navigationMap = {};",
-            serde_json::to_string(&self.paths)
-                .expect("serialization of the navigation map should not fail")
-        )
-    }
-}
-
-#[derive(Debug, Clone, Default)]
-pub struct NavigationMapBuilder {
-    stack: Vec<String>,
-    navigation_map: NavigationMap,
-}
-
-impl NavigationMapBuilder {
-    pub fn enter_tree(&mut self, tree: String) {
-        self.stack.push(tree.clone());
-        self.navigation_map.paths.insert(tree, self.stack.clone());
-    }
-
-    pub fn exit_tree(&mut self) {
-        self.stack.pop();
-    }
-
-    pub fn finish(self) -> NavigationMap {
-        self.navigation_map
-    }
-}
-
-pub fn build_navigation_map(treehouse: &Treehouse, root_tree_path: &str) -> NavigationMap {
         let mut builder = NavigationMapBuilder::default();
 
         fn rec_branch(
@@ -79,4 +68,5 @@ pub fn build_navigation_map(treehouse: &Treehouse, root_tree_path: &str) -> Navi
         rec_tree(treehouse, &mut builder, root_tree_path);
 
         builder.finish()
+    }
 }

crates/treehouse/src/html/tree.rs

@@ -3,25 +3,23 @@ use std::{borrow::Cow, fmt::Write};
 use treehouse_format::pull::BranchKind;
 
 use crate::{
-    cli::Paths,
     config::Config,
+    dirs::Dirs,
     html::EscapeAttribute,
     state::{FileId, Treehouse},
     tree::{
         attributes::{Content, Stage},
         mini_template, SemaBranchId,
     },
-    vfs::{CdExt, ReadFilesystem, VPathBuf},
 };
 
 use super::{djot, EscapeHtml};
 
 pub fn branch_to_html(
     s: &mut String,
-    treehouse: &mut Treehouse,
+    treehouse: &Treehouse,
     config: &Config,
-    root_fs: &dyn ReadFilesystem, // TODO: Lower privileges
+    dirs: &Dirs,
-    paths: &Paths<'_>,
     file_id: FileId,
     branch_id: SemaBranchId,
 ) {
@@ -116,13 +114,7 @@ pub fn branch_to_html(
         }
 
         if branch.attributes.template {
-            final_markup = mini_template::render(
+            final_markup = mini_template::render(config, treehouse, dirs, &final_markup);
-                config,
-                treehouse,
-                paths,
-                &root_fs.cd(VPathBuf::new("static/pics")),
-                &final_markup,
-            );
         }
         s.push_str("<th-bc>");
 
@@ -137,8 +129,7 @@ pub fn branch_to_html(
                 .to_owned(),
 
             config,
-            emoji_fs: &root_fs.cd(VPathBuf::new("static/emoji")),
+            dirs,
-            pics_fs: &root_fs.cd(VPathBuf::new("static/pics")),
 
             treehouse,
             file_id,
@@ -195,7 +186,7 @@ pub fn branch_to_html(
                 let num_children = branch.children.len();
                 for i in 0..num_children {
                     let child_id = treehouse.tree.branch(branch_id).children[i];
-                    branch_to_html(s, treehouse, config, root_fs, paths, file_id, child_id);
+                    branch_to_html(s, treehouse, config, dirs, file_id, child_id);
                 }
                 s.push_str("</ul>");
             }
@@ -209,16 +200,15 @@ pub fn branch_to_html(
 
 pub fn branches_to_html(
     s: &mut String,
-    treehouse: &mut Treehouse,
+    treehouse: &Treehouse,
     config: &Config,
-    root_fs: &dyn ReadFilesystem, // TODO: Lower privileges
+    dirs: &Dirs,
-    paths: &Paths<'_>,
     file_id: FileId,
     branches: &[SemaBranchId],
 ) {
     s.push_str("<ul>");
     for &child in branches {
-        branch_to_html(s, treehouse, config, root_fs, paths, file_id, child);
+        branch_to_html(s, treehouse, config, dirs, file_id, child);
     }
     s.push_str("</ul>");
 }

crates/treehouse/src/import_map.rs

@@ -1,11 +1,9 @@
-use std::{ffi::OsStr, path::PathBuf};
+use std::ops::ControlFlow;
 
 use indexmap::IndexMap;
-use log::warn;
 use serde::{Deserialize, Serialize};
-use walkdir::WalkDir;
 
-use crate::static_urls::StaticUrls;
+use crate::vfs::{self, Dir, VPathBuf};
 
 #[derive(Debug, Clone, Serialize)]
 pub struct ImportMap {
@@ -15,49 +13,30 @@ pub struct ImportMap {
 #[derive(Debug, Clone, Deserialize, Serialize)]
 pub struct ImportRoot {
     pub name: String,
-    pub path: String,
+    pub path: VPathBuf,
 }
 
 impl ImportMap {
-    pub fn generate(base_url: String, import_roots: &[ImportRoot]) -> Self {
+    pub fn generate(site: &str, root: &dyn Dir, import_roots: &[ImportRoot]) -> Self {
         let mut import_map = ImportMap {
             imports: IndexMap::new(),
         };
 
-        for root in import_roots {
+        for import_root in import_roots {
-            let static_urls = StaticUrls::new(
+            vfs::walk_dir_rec(root, &import_root.path, &mut |path| {
-                PathBuf::from(&root.path),
+                if path.extension() == Some("js") {
-                format!("{base_url}/{}", root.path),
+                    import_map.imports.insert(
+                        format!(
+                            "{}/{}",
+                            import_root.name,
+                            path.strip_prefix(&import_root.path).unwrap_or(path)
+                        ),
+                        vfs::url(site, root, path)
+                            .expect("import directory is not anchored anywhere"),
                     );
-            for entry in WalkDir::new(&root.path) {
-                let entry = match entry {
-                    Ok(entry) => entry,
-                    Err(error) => {
-                        warn!("directory walk failed: {error}");
-                        continue;
-                    }
-                };
-
-                if !entry.file_type().is_dir() && entry.path().extension() == Some(OsStr::new("js"))
-                {
-                    let normalized_path = entry
-                        .path()
-                        .strip_prefix(&root.path)
-                        .unwrap_or(entry.path())
-                        .to_string_lossy()
-                        .replace('\\', "/");
-                    match static_urls.get(&normalized_path) {
-                        Ok(url) => {
-                            import_map
-                                .imports
-                                .insert(format!("{}/{normalized_path}", root.name), url);
-                        }
-                        Err(error) => {
-                            warn!("could not get static url for {normalized_path}: {error}")
-                        }
-                    }
-                }
                 }
+                ControlFlow::Continue(())
+            });
         }
 
         import_map.imports.sort_unstable_keys();

crates/treehouse/src/include_static.rs

@@ -1,28 +0,0 @@
-use std::path::PathBuf;
-
-use handlebars::{Context, Handlebars, Helper, HelperDef, RenderContext, RenderError, ScopedJson};
-use serde_json::Value;
-
-pub struct IncludeStatic {
-    pub base_dir: PathBuf,
-}
-
-impl HelperDef for IncludeStatic {
-    fn call_inner<'reg: 'rc, 'rc>(
-        &self,
-        helper: &Helper<'reg, 'rc>,
-        _: &'reg Handlebars<'reg>,
-        _: &'rc Context,
-        _: &mut RenderContext<'reg, 'rc>,
-    ) -> Result<ScopedJson<'reg, 'rc>, RenderError> {
-        if let Some(param) = helper.param(0).and_then(|v| v.value().as_str()) {
-            return Ok(ScopedJson::Derived(Value::String(
-                std::fs::read_to_string(self.base_dir.join(param)).map_err(|error| {
-                    RenderError::new(format!("cannot read static asset {param}: {error}"))
-                })?,
-            )));
-        }
-
-        Err(RenderError::new("asset path must be provided"))
-    }
-}

crates/treehouse/src/lib.rs

@@ -1,15 +1,13 @@
 pub mod cli;
 pub mod config;
+pub mod dirs;
 pub mod fun;
 pub mod generate;
 pub mod history;
 pub mod html;
 pub mod import_map;
-pub mod include_static;
 pub mod parse;
 pub mod paths;
 pub mod state;
-pub mod static_urls;
-pub mod templater;
 pub mod tree;
 pub mod vfs;

crates/treehouse/src/main.rs

@@ -1,76 +1,78 @@
+use std::fs;
 use std::path::PathBuf;
-use std::{fs, path::Path};
+use std::sync::Arc;
 
+use anyhow::Context;
 use clap::Parser;
 use log::error;
-use treehouse::generate::{regenerate_or_report_error, LatestRevision};
+use treehouse::cli::serve::serve;
-use treehouse::vfs::PhysicalDir;
+use treehouse::dirs::Dirs;
-use treehouse::vfs::{AnchoredAtExt, VPathBuf};
+use treehouse::generate::{self, Sources};
+use treehouse::vfs::asynch::AsyncDir;
+use treehouse::vfs::{AnchoredAtExt, DynDir, ToDynDir, VPathBuf};
+use treehouse::vfs::{Cd, PhysicalDir};
 use treehouse::{
     cli::{
         fix::{fix_all_cli, fix_file_cli},
-        serve::serve,
         wc::wc_cli,
-        Command, Paths, ProgramArgs,
+        Command, ProgramArgs,
     },
-    vfs::{BufferedFile, MountPoints, ReadFilesystem, VPath},
+    vfs::{BufferedFile, MemDir, VPath},
 };
 
-fn vfs_sources() -> anyhow::Result<impl ReadFilesystem> {
+fn vfs_sources() -> anyhow::Result<DynDir> {
-    let mut root = MountPoints::new();
+    let mut root = MemDir::new();
 
     root.add(
         VPath::new("treehouse.toml"),
-        Box::new(BufferedFile::new(fs::read("treehouse.toml")?)),
+        BufferedFile::new(fs::read("treehouse.toml")?).to_dyn(),
     );
     root.add(
         VPath::new("static"),
-        Box::new(PhysicalDir::new(PathBuf::from("static")).anchored_at(VPathBuf::new("static"))),
+        PhysicalDir::new(PathBuf::from("static"))
+            .anchored_at(VPathBuf::new("static"))
+            .to_dyn(),
     );
     root.add(
         VPath::new("template"),
-        Box::new(PhysicalDir::new(PathBuf::from("template"))),
+        PhysicalDir::new(PathBuf::from("template")).to_dyn(),
     );
     root.add(
         VPath::new("content"),
-        Box::new(PhysicalDir::new(PathBuf::from("content"))),
+        PhysicalDir::new(PathBuf::from("content")).to_dyn(),
     );
 
-    Ok(root)
+    Ok(root.to_dyn())
 }
 
 async fn fallible_main() -> anyhow::Result<()> {
     let args = ProgramArgs::parse();
 
-    let paths = Paths {
-        target_dir: Path::new("target/site"),
-        template_target_dir: Path::new("target/site/static/html"),
-
-        config_file: Path::new("treehouse.toml"),
-        static_dir: Path::new("static"),
-        template_dir: Path::new("template"),
-        content_dir: Path::new("content"),
-    };
-
     let src = vfs_sources()?;
+    let dirs = Arc::new(Dirs {
+        root: src.clone(),
+        content: Cd::new(src.clone(), VPathBuf::new("content")).to_dyn(),
+        static_: Cd::new(src.clone(), VPathBuf::new("static")).to_dyn(),
+        template: Cd::new(src.clone(), VPathBuf::new("template")).to_dyn(),
+        pics: Cd::new(src.clone(), VPathBuf::new("static/pics")).to_dyn(),
+        emoji: Cd::new(src.clone(), VPathBuf::new("static/emoji")).to_dyn(),
+        syntax: Cd::new(src.clone(), VPathBuf::new("static/syntax")).to_dyn(),
+    });
 
     match args.command {
         Command::Serve {
-            generate: generate_args,
+            generate: _,
             serve: serve_args,
         } => {
-            let latest_revision = match generate_args.commits_only {
+            let sources = Arc::new(Sources::load(&dirs).context("failed to load sources")?);
-                true => LatestRevision::LatestCommit,
+            let target = generate::target(dirs, sources.clone());
-                false => LatestRevision::WorkingTree,
+            serve(sources, AsyncDir::new(target), serve_args.port).await?;
-            };
-            let (config, treehouse) = regenerate_or_report_error(&paths, &src, latest_revision)?;
-            serve(config, treehouse, &paths, serve_args.port).await?;
         }
 
-        Command::Fix(fix_args) => fix_file_cli(fix_args)?,
+        Command::Fix(fix_args) => fix_file_cli(fix_args, &*dirs.content)?.apply().await?,
-        Command::FixAll(fix_args) => fix_all_cli(fix_args, &paths)?,
+        Command::FixAll(fix_args) => fix_all_cli(fix_args, &*dirs.content)?.apply().await?,
 
-        Command::Wc(wc_args) => wc_cli(paths.content_dir, wc_args)?,
+        Command::Wc(wc_args) => wc_cli(&dirs.content, wc_args)?,
 
         Command::Ulid => {
             let mut rng = rand::thread_rng();

crates/treehouse/src/state.rs

@@ -1,4 +1,4 @@
-use std::{collections::HashMap, ops::Range, path::PathBuf};
+use std::{collections::HashMap, ops::Range};
 
 use anyhow::Context;
 use codespan_reporting::{
@@ -6,26 +6,19 @@ use codespan_reporting::{
     files::SimpleFiles,
     term::termcolor::{ColorChoice, StandardStream},
 };
-use serde::Serialize;
 use ulid::Ulid;
 
-use crate::tree::{SemaBranchId, SemaRoots, SemaTree};
+use crate::{
-
+    tree::{SemaBranchId, SemaRoots, SemaTree},
-#[derive(Debug, Clone, Serialize)]
+    vfs::VPathBuf,
-pub struct RevisionInfo {
+};
-    pub is_latest: bool,
-    pub number: usize,
-    pub commit: String,
-    pub commit_short: String,
-}
 
 #[derive(Debug, Clone)]
 pub enum Source {
     Tree {
         input: String,
         tree_path: String,
-        target_path: PathBuf,
+        target_path: VPathBuf,
-        revision_info: RevisionInfo,
     },
     Other(String),
 }
@@ -103,13 +96,6 @@ impl Treehouse {
         }
     }
 
-    pub fn revision_info(&self, file_id: FileId) -> Option<&RevisionInfo> {
-        match self.source(file_id) {
-            Source::Tree { revision_info, .. } => Some(revision_info),
-            Source::Other(_) => None,
-        }
-    }
-
     pub fn next_missingno(&mut self) -> Ulid {
         self.missingno_generator
             .generate()

crates/treehouse/src/static_urls.rs

@@ -1,89 +0,0 @@
-use std::{
-    collections::HashMap,
-    fs::File,
-    io::{self, BufReader},
-    path::PathBuf,
-    sync::{Mutex, RwLock},
-};
-
-use handlebars::{Context, Handlebars, Helper, HelperDef, RenderContext, RenderError, ScopedJson};
-use serde_json::Value;
-
-pub struct StaticUrls {
-    base_dir: PathBuf,
-    base_url: String,
-    // Really annoying that we have to use an RwLock for this. We only ever generate in a
-    // single-threaded environment.
-    // Honestly it would be a lot more efficient if Handlebars just assumed single-threadedness
-    // and required you to clone it over to different threads.
-    // Stuff like this is why I really want to implement my own templating engine...
-    hash_cache: RwLock<HashMap<String, String>>,
-    missing_files: Mutex<Vec<MissingFile>>,
-}
-
-pub struct MissingFile {
-    pub path: String,
-}
-
-impl StaticUrls {
-    pub fn new(base_dir: PathBuf, base_url: String) -> Self {
-        Self {
-            base_dir,
-            base_url,
-            hash_cache: RwLock::new(HashMap::new()),
-            missing_files: Mutex::new(vec![]),
-        }
-    }
-
-    pub fn get(&self, filename: &str) -> Result<String, io::Error> {
-        let hash_cache = self.hash_cache.read().unwrap();
-        if let Some(cached) = hash_cache.get(filename) {
-            return Ok(cached.to_owned());
-        }
-        drop(hash_cache);
-
-        let mut hasher = blake3::Hasher::new();
-        let file = BufReader::new(File::open(self.base_dir.join(filename))?);
-        hasher.update_reader(file)?;
-        // NOTE: Here the hash is truncated to 8 characters. This is fine, because we don't
-        // care about security here - only detecting changes in files.
-        let hash = format!(
-            "{}/{}?cache=b3-{}",
-            self.base_url,
-            filename,
-            &hasher.finalize().to_hex()[0..8]
-        );
-        {
-            let mut hash_cache = self.hash_cache.write().unwrap();
-            hash_cache.insert(filename.to_owned(), hash.clone());
-        }
-        Ok(hash)
-    }
-
-    pub fn take_missing_files(&self) -> Vec<MissingFile> {
-        std::mem::take(&mut self.missing_files.lock().unwrap())
-    }
-}
-
-impl HelperDef for StaticUrls {
-    fn call_inner<'reg: 'rc, 'rc>(
-        &self,
-        helper: &Helper<'reg, 'rc>,
-        _: &'reg Handlebars<'reg>,
-        _: &'rc Context,
-        _: &mut RenderContext<'reg, 'rc>,
-    ) -> Result<ScopedJson<'reg, 'rc>, RenderError> {
-        if let Some(param) = helper.param(0).and_then(|v| v.value().as_str()) {
-            return Ok(ScopedJson::Derived(Value::String(
-                self.get(param).unwrap_or_else(|_| {
-                    self.missing_files.lock().unwrap().push(MissingFile {
-                        path: param.to_owned(),
-                    });
-                    format!("{}/{}", self.base_url, param)
-                }),
-            )));
-        }
-
-        Err(RenderError::new("asset path must be provided"))
-    }
-}

crates/treehouse/src/templater.rs

@@ -1,13 +0,0 @@
-use handlebars::Handlebars;
-
-pub struct Templater {
-    handlebars: Handlebars<'static>,
-}
-
-impl Templater {
-    pub fn new() -> Self {
-        Self {
-            handlebars: Handlebars::new(),
-        }
-    }
-}

crates/treehouse/src/tree.rs

@@ -163,13 +163,7 @@ impl SemaBranch {
     ) -> SemaBranchId {
         let attributes = Self::parse_attributes(treehouse, diagnostics, file_id, &branch);
 
-        let revision_info = treehouse
+        let named_id = attributes.id.to_owned();
-            .revision_info(file_id)
-            .expect(".tree files must have Tree-type sources");
-        let named_id = match revision_info.is_latest {
-            true => attributes.id.to_owned(),
-            false => format!("{}@{}", attributes.id, revision_info.commit_short),
-        };
         let html_id = format!(
             "{}:{}",
             treehouse.tree_path(file_id).unwrap(),

crates/treehouse/src/tree/mini_template.rs

@@ -7,7 +7,13 @@
 use std::fmt::Write;
 use std::ops::Range;
 
-use crate::{cli::Paths, config::Config, html::EscapeHtml, state::Treehouse, vfs::ReadFilesystem};
+use crate::{
+    config::Config,
+    dirs::Dirs,
+    html::EscapeHtml,
+    state::Treehouse,
+    vfs::{Dir, VPath},
+};
 
 struct Lexer<'a> {
     input: &'a str,
@@ -148,13 +154,7 @@ impl Renderer<'_> {
         self.output.push_str(&self.lexer.input[token.range.clone()]);
     }
 
-    fn render(
+    fn render(&mut self, config: &Config, treehouse: &Treehouse, dirs: &Dirs) {
-        &mut self,
-        config: &Config,
-        treehouse: &Treehouse,
-        paths: &Paths<'_>,
-        pics_fs: &dyn ReadFilesystem,
-    ) {
         let kind_of = |token: &Token| token.kind;
 
         while let Some(token) = self.lexer.next() {
@@ -171,8 +171,7 @@ impl Renderer<'_> {
                         match Self::render_template(
                             config,
                             treehouse,
-                            pics_fs,
+                            dirs,
-                            paths,
                             self.lexer.input[inside.as_ref().unwrap().range.clone()].trim(),
                         ) {
                             Ok(s) => match escaping {
@@ -199,31 +198,27 @@ impl Renderer<'_> {
     fn render_template(
         config: &Config,
         _treehouse: &Treehouse,
-        pics_fs: &dyn ReadFilesystem,
+        dirs: &Dirs,
-        paths: &Paths<'_>,
         template: &str,
     ) -> Result<String, InvalidTemplate> {
         let (function, arguments) = template.split_once(' ').unwrap_or((template, ""));
         match function {
-            "pic" => Ok(config.pic_url(pics_fs, arguments)),
+            "pic" => Ok(config.pic_url(&*dirs.pics, arguments)),
-            "include_static" => std::fs::read_to_string(paths.static_dir.join(arguments))
+            "include_static" => VPath::try_new(arguments)
-                .map_err(|_| InvalidTemplate),
+                .ok()
+                .and_then(|vpath| dirs.static_.content(vpath))
+                .and_then(|content| String::from_utf8(content).ok())
+                .ok_or(InvalidTemplate),
             _ => Err(InvalidTemplate),
         }
     }
 }
 
-pub fn render(
+pub fn render(config: &Config, treehouse: &Treehouse, dirs: &Dirs, input: &str) -> String {
-    config: &Config,
-    treehouse: &Treehouse,
-    paths: &Paths<'_>,
-    pics_fs: &dyn ReadFilesystem,
-    input: &str,
-) -> String {
     let mut renderer = Renderer {
         lexer: Lexer::new(input),
         output: String::new(),
     };
-    renderer.render(config, treehouse, paths, pics_fs);
+    renderer.render(config, treehouse, dirs);
     renderer.output
 }

crates/treehouse/src/vfs.rs

@@ -1,250 +1,82 @@
+//! The treehouse virtual file system.
+//!
+//! Unlike traditional file systems, there is no separation between directories and files.
+//! Instead, our file system is based on _entries_, which may have specific, optional, well-typed
+//! metadata attached to them.
+//! A directory is formed by returning a list of paths from [`dir`][Dir::dir], and a file is
+//! formed by returning `Some` from [`content`][Dir::content].
+//!
+//! This makes using the file system simpler, as you do not have to differentiate between different
+//! entry kinds. All paths act as if they _could_ return byte content, and all paths act as if they
+//! _could_ have children.
+//!
+//! # Composability
+//!
+//! [`Dir`]s are composable. The [`Dir`] itself starts off with the root path ([`VPath::ROOT`]),
+//! which may contain further [`dir`][Dir::dir] entries, or content by itself.
+//! This makes it possible to nest a [`Dir`] under another [`Dir`].
+//!
+//! Additionally, there's also the inverse operation, [`Cd`] (named after the `cd`
+//! _change directory_ shell command), which returns a [`Dir`] viewing a subpath within another
+//! [`Dir`].
+//!
+//! # Building directories
+//!
+//! In-memory directories can be composed using the following primitives:
+//!
+//! - [`EmptyEntry`] - has no metadata whatsoever.
+//! - [`BufferedFile`] - root path content is the provided byte vector.
+//! - [`MemDir`] - a [`Dir`] containing a single level of other [`Dir`]s inside.
+//!
+//! Additionally, for interfacing with the OS file system, [`PhysicalDir`] is available,
+//! representing a directory stored on the disk.
+//!
+//! # Virtual paths
+//!
+//! Entries within directories are referenced using [`VPath`]s (**v**irtual **path**s).
+//! A virtual path is composed out of any amount of `/`-separated components.
+//!
+//! There are no special directories like `.` and `..` (those are just normal entries, though using
+//! them is discouraged). [`VPath`]s are always relative to the root of the [`Dir`] you're querying.
+//!
+//! A leading or trailing slash is not allowed, because they would have no meaning.
+//!
+//! [`VPath`] also has an owned version, [`VPathBuf`].
+
 use std::{
-    borrow::Borrow,
     fmt::{self, Debug},
     ops::{ControlFlow, Deref},
+    sync::Arc,
 };
 
-use anyhow::ensure;
-use serde::{Deserialize, Serialize};
-
 mod anchored;
+pub mod asynch;
 mod cd;
+mod edit;
 mod empty;
 mod file;
-mod mount_points;
+mod mem_dir;
+mod overlay;
+mod path;
 mod physical;
 
 pub use anchored::*;
 pub use cd::*;
+pub use edit::*;
 pub use empty::*;
 pub use file::*;
-pub use mount_points::*;
+pub use mem_dir::*;
+pub use overlay::*;
+pub use path::*;
 pub use physical::*;
 
-#[derive(PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct VPath {
-    path: str,
-}
-
-impl VPath {
-    pub const SEPARATOR: char = '/';
-    pub const ROOT: &Self = unsafe { Self::new_unchecked("") };
-
-    pub fn try_new(s: &str) -> anyhow::Result<&Self> {
-        ensure!(
-            !s.ends_with(Self::SEPARATOR),
-            "path must not end with '{}' (got {s:?})",
-            Self::SEPARATOR
-        );
-        ensure!(
-            !s.starts_with(Self::SEPARATOR),
-            "paths are always absolute and must not start with '{}' (got {s:?})",
-            Self::SEPARATOR
-        );
-
-        Ok(unsafe { Self::new_unchecked(s) })
-    }
-
-    pub fn new(s: &str) -> &Self {
-        Self::try_new(s).expect("invalid path")
-    }
-
-    const unsafe fn new_unchecked(s: &str) -> &Self {
-        std::mem::transmute::<_, &Self>(s)
-    }
-
-    pub fn try_join(&self, sub: &str) -> anyhow::Result<VPathBuf> {
-        let mut buf = VPathBuf::from(self);
-        if !sub.is_empty() {
-            let sub = VPath::try_new(sub)?;
-            buf.path.push('/');
-            buf.path.push_str(&sub.path);
-        }
-        Ok(buf)
-    }
-
-    pub fn join(&self, sub: &str) -> VPathBuf {
-        self.try_join(sub).expect("invalid subpath")
-    }
-
-    pub fn strip_prefix(&self, prefix: &VPath) -> Option<&Self> {
-        if self == prefix {
-            Some(VPath::ROOT)
-        } else {
-            self.path
-                .strip_prefix(&prefix.path)
-                .and_then(|p| p.strip_prefix('/'))
-                // SAFETY: If `self` starts with `prefix`, `p` will end up not being prefixed by `self`
-                // nor a leading slash.
-                .map(|p| unsafe { VPath::new_unchecked(p) })
-        }
-    }
-
-    pub fn depth(&self) -> usize {
-        self.path.chars().filter(|&c| c == Self::SEPARATOR).count()
-    }
-
-    pub fn segments(&self) -> impl Iterator<Item = &Self> {
-        self.as_str().split(Self::SEPARATOR).map(|s| unsafe {
-            // SAFETY: Since we're splitting on the separator, the path cannot start or end with it.
-            Self::new_unchecked(s)
-        })
-    }
-
-    pub fn rsegments(&self) -> impl Iterator<Item = &Self> {
-        self.as_str().rsplit(Self::SEPARATOR).map(|s| unsafe {
-            // SAFETY: Since we're splitting on the separator, the path cannot start or end with it.
-            Self::new_unchecked(s)
-        })
-    }
-
-    pub fn file_name(&self) -> Option<&str> {
-        self.rsegments().next().map(Self::as_str)
-    }
-
-    pub fn extension(&self) -> Option<&str> {
-        let file_name = self.file_name()?;
-        let (left, right) = file_name.rsplit_once('.')?;
-        if left.is_empty() {
-            None
-        } else {
-            Some(right)
-        }
-    }
-
-    pub fn file_stem(&self) -> Option<&str> {
-        let file_name = self.file_name()?;
-        if let Some(extension) = self.extension() {
-            Some(&file_name[..file_name.len() - extension.len() - 1])
-        } else {
-            Some(file_name)
-        }
-    }
-
-    pub fn as_str(&self) -> &str {
-        &self.path
-    }
-}
-
-impl ToOwned for VPath {
-    type Owned = VPathBuf;
-
-    fn to_owned(&self) -> Self::Owned {
-        VPathBuf::from(self)
-    }
-}
-
-impl fmt::Debug for VPath {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.write_str(&self.path)
-    }
-}
-
-impl fmt::Display for VPath {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.write_str(&self.path)
-    }
-}
-
-#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct VPathBuf {
-    path: String,
-}
-
-impl VPathBuf {
-    pub fn new(path: impl Into<String>) -> Self {
-        Self::try_new(path).expect("invalid path")
-    }
-
-    pub fn try_new(path: impl Into<String>) -> anyhow::Result<Self> {
-        let path = path.into();
-        match VPath::try_new(&path) {
-            Ok(_) => Ok(Self { path }),
-            Err(e) => Err(e),
-        }
-    }
-
-    unsafe fn new_unchecked(path: String) -> Self {
-        Self { path }
-    }
-}
-
-impl Deref for VPathBuf {
-    type Target = VPath;
-
-    fn deref(&self) -> &Self::Target {
-        unsafe { VPath::new_unchecked(&self.path) }
-    }
-}
-
-impl fmt::Debug for VPathBuf {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.write_str(&self.path)
-    }
-}
-
-impl fmt::Display for VPathBuf {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.write_str(&self.path)
-    }
-}
-
-impl From<&VPath> for VPathBuf {
-    fn from(value: &VPath) -> Self {
-        unsafe { Self::new_unchecked(value.path.to_owned()) }
-    }
-}
-
-impl Borrow<VPath> for VPathBuf {
-    fn borrow(&self) -> &VPath {
-        self
-    }
-}
-
-impl<'de> Deserialize<'de> for VPathBuf {
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: serde::Deserializer<'de>,
-    {
-        use serde::de;
-
-        struct Visitor;
-
-        impl de::Visitor<'_> for Visitor {
-            type Value = VPathBuf;
-
-            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-                formatter.write_str("virtual path")
-            }
-
-            fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
-            where
-                E: de::Error,
-            {
-                VPathBuf::try_new(v).map_err(de::Error::custom)
-            }
-        }
-
-        deserializer.deserialize_str(Visitor)
-    }
-}
-
-impl Serialize for VPathBuf {
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        S: serde::Serializer,
-    {
-        serializer.serialize_str(self.as_str())
-    }
-}
-
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub struct DirEntry {
     pub path: VPathBuf,
 }
 
-pub trait ReadFilesystem: Debug {
+pub trait Dir: Debug {
-    /// List all files under the provided path.
+    /// List all entries under the provided path.
     fn dir(&self, path: &VPath) -> Vec<DirEntry>;
 
     /// Return the byte content of the entry at the given path.
@@ -264,14 +96,96 @@ pub trait ReadFilesystem: Debug {
         None
     }
 
-    /// Optimization for [`ReadFilesystemCombinators::cd`] that allows for avoiding wrapping
+    /// If a file can be written persistently, returns an [`EditPath`] representing the file in
-    /// `Cd`s in `Cd`s.
+    /// persistent storage.
-    #[doc(hidden)]
+    ///
-    fn cd_optimization(&self, _subpath: &VPath) -> Option<Cd<'_>> {
+    /// An edit path can then be made into an [`Edit`].
+    fn edit_path(&self, _path: &VPath) -> Option<EditPath> {
         None
     }
 }
 
+impl<T> Dir for &T
+where
+    T: Dir,
+{
+    fn dir(&self, path: &VPath) -> Vec<DirEntry> {
+        (**self).dir(path)
+    }
+
+    fn content(&self, path: &VPath) -> Option<Vec<u8>> {
+        (**self).content(path)
+    }
+
+    fn content_version(&self, path: &VPath) -> Option<String> {
+        (**self).content_version(path)
+    }
+
+    fn anchor(&self, path: &VPath) -> Option<VPathBuf> {
+        (**self).anchor(path)
+    }
+
+    fn edit_path(&self, path: &VPath) -> Option<EditPath> {
+        (**self).edit_path(path)
+    }
+}
+
+#[derive(Clone)]
+pub struct DynDir {
+    arc: Arc<dyn Dir + Send + Sync>,
+}
+
+impl Dir for DynDir {
+    fn dir(&self, path: &VPath) -> Vec<DirEntry> {
+        self.arc.dir(path)
+    }
+
+    fn content(&self, path: &VPath) -> Option<Vec<u8>> {
+        self.arc.content(path)
+    }
+
+    fn content_version(&self, path: &VPath) -> Option<String> {
+        self.arc.content_version(path)
+    }
+
+    fn anchor(&self, path: &VPath) -> Option<VPathBuf> {
+        self.arc.anchor(path)
+    }
+
+    fn edit_path(&self, path: &VPath) -> Option<EditPath> {
+        self.arc.edit_path(path)
+    }
+}
+
+impl fmt::Debug for DynDir {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&*self.arc, f)
+    }
+}
+
+impl Deref for DynDir {
+    type Target = dyn Dir + Send + Sync;
+
+    fn deref(&self) -> &Self::Target {
+        &*self.arc
+    }
+}
+
+pub trait ToDynDir {
+    fn to_dyn(self) -> DynDir;
+}
+
+impl<T> ToDynDir for T
+where
+    T: Dir + Send + Sync + 'static,
+{
+    fn to_dyn(self) -> DynDir {
+        DynDir {
+            arc: Arc::new(self),
+        }
+    }
+}
+
 pub trait AnchoredAtExt {
     fn anchored_at(self, at: VPathBuf) -> Anchored<Self>
     where
@@ -280,53 +194,28 @@ pub trait AnchoredAtExt {
 
 impl<T> AnchoredAtExt for T
 where
-    T: ReadFilesystem,
+    T: Dir,
 {
     fn anchored_at(self, at: VPathBuf) -> Anchored<Self> {
         Anchored::new(self, at)
     }
 }
 
-pub trait CdExt {
+pub fn walk_dir_rec(dir: &dyn Dir, path: &VPath, f: &mut dyn FnMut(&VPath) -> ControlFlow<(), ()>) {
-    fn cd<'a>(self, into: VPathBuf) -> Cd<'a>
+    for entry in dir.dir(path) {
-    where
-        Self: 'a;
-}
-
-impl CdExt for &dyn ReadFilesystem {
-    fn cd<'a>(self, into: VPathBuf) -> Cd<'a>
-    where
-        Self: 'a,
-    {
-        if let Some(cd) = self.cd_optimization(&into) {
-            cd
-        } else {
-            Cd::new(self, into)
-        }
-    }
-}
-
-pub fn walk_rec(
-    fs: &dyn ReadFilesystem,
-    path: &VPath,
-    f: &mut dyn FnMut(&VPath) -> ControlFlow<(), ()>,
-) {
-    for entry in fs.dir(path) {
         match f(&entry.path) {
             ControlFlow::Continue(_) => (),
             ControlFlow::Break(_) => return,
         }
-        walk_rec(fs, &entry.path, f);
+        walk_dir_rec(dir, &entry.path, f);
     }
 }
 
-pub fn url(site: &str, fs: &dyn ReadFilesystem, path: &VPath) -> String {
+pub fn url(site: &str, dir: &dyn Dir, path: &VPath) -> Option<String> {
-    let Some(anchor) = fs.anchor(path) else {
+    let anchor = dir.anchor(path)?;
-        panic!("filesystem {fs:?} is not anchored anywhere and a URL of it cannot be produced")
+    if let Some(version) = dir.content_version(path) {
-    };
+        Some(format!("{}/{anchor}?v={version}", site))
-    if let Some(version) = fs.content_version(path) {
-        format!("{}/{anchor}?v={version}", site)
     } else {
-        format!("{}/{anchor}", site)
+        Some(format!("{}/{anchor}", site))
     }
 }

crates/treehouse/src/vfs/anchored.rs

@@ -1,6 +1,6 @@
 use std::fmt;
 
-use super::{DirEntry, ReadFilesystem, VPath, VPathBuf};
+use super::{Dir, DirEntry, VPath, VPathBuf};
 
 pub struct Anchored<T> {
     inner: T,
@@ -13,9 +13,9 @@ impl<T> Anchored<T> {
     }
 }
 
-impl<T> ReadFilesystem for Anchored<T>
+impl<T> Dir for Anchored<T>
 where
-    T: ReadFilesystem,
+    T: Dir,
 {
     fn dir(&self, path: &VPath) -> Vec<DirEntry> {
         self.inner.dir(path)
@@ -30,7 +30,7 @@ where
     }
 
     fn anchor(&self, path: &VPath) -> Option<VPathBuf> {
-        Some(self.at.join(path.as_str()))
+        Some(self.at.join(path))
     }
 }
 

crates/treehouse/src/vfs/asynch.rs

@@ -0,0 +1,23 @@
+use super::{Dir, DynDir, VPath};
+
+#[derive(Debug, Clone)]
+pub struct AsyncDir {
+    inner: DynDir,
+}
+
+impl AsyncDir {
+    pub fn new(inner: DynDir) -> Self {
+        Self { inner }
+    }
+
+    pub async fn content(&self, path: &VPath) -> Option<Vec<u8>> {
+        let this = self.clone();
+        let path = path.to_owned();
+        // NOTE: Performance impact of spawning a blocking task may be a bit high in case
+        // we add caching.
+        // Measure throughput here.
+        tokio::task::spawn_blocking(move || this.inner.content(&path))
+            .await
+            .unwrap()
+    }
+}

crates/treehouse/src/vfs/cd.rs

@@ -1,22 +1,25 @@
 use std::fmt;
 
-use super::{DirEntry, ReadFilesystem, VPath, VPathBuf};
+use super::{Dir, DirEntry, EditPath, VPath, VPathBuf};
 
-pub struct Cd<'fs> {
+pub struct Cd<T> {
-    parent: &'fs dyn ReadFilesystem,
+    parent: T,
     path: VPathBuf,
 }
 
-impl<'fs> Cd<'fs> {
+impl<T> Cd<T> {
-    pub fn new(parent: &'fs dyn ReadFilesystem, path: VPathBuf) -> Self {
+    pub fn new(parent: T, path: VPathBuf) -> Self {
         Self { parent, path }
     }
 }
 
-impl ReadFilesystem for Cd<'_> {
+impl<T> Dir for Cd<T>
+where
+    T: Dir,
+{
     fn dir(&self, path: &VPath) -> Vec<DirEntry> {
         self.parent
-            .dir(&self.path.join(path.as_str()))
+            .dir(&self.path.join(path))
             .into_iter()
             .map(|entry| DirEntry {
                 path: entry
@@ -29,23 +32,26 @@ impl ReadFilesystem for Cd<'_> {
     }
 
     fn content_version(&self, path: &VPath) -> Option<String> {
-        self.parent.content_version(&self.path.join(path.as_str()))
+        self.parent.content_version(&self.path.join(path))
     }
 
     fn content(&self, path: &VPath) -> Option<Vec<u8>> {
-        self.parent.content(&self.path.join(path.as_str()))
+        self.parent.content(&self.path.join(path))
     }
 
     fn anchor(&self, path: &VPath) -> Option<VPathBuf> {
-        self.parent.anchor(&self.path.join(path.as_str()))
+        self.parent.anchor(&self.path.join(path))
     }
 
-    fn cd_optimization(&self, subpath: &VPath) -> Option<Cd<'_>> {
+    fn edit_path(&self, path: &VPath) -> Option<EditPath> {
-        Some(Cd::new(self, subpath.to_owned()))
+        self.parent.edit_path(&self.path.join(path))
     }
 }
 
-impl fmt::Debug for Cd<'_> {
+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)
     }

crates/treehouse/src/vfs/edit.rs

@@ -0,0 +1,92 @@
+use std::{error::Error, fmt, future::Future, path::PathBuf};
+
+use log::{error, info};
+use tokio::task::JoinSet;
+
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct EditPath {
+    pub(super) path: PathBuf,
+}
+
+/// Represents a pending edit operation that can be written to persistent storage later.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Edit {
+    /// An edit that doesn't do anything.
+    NoOp,
+
+    /// Write the given string to a file.
+    Write(EditPath, String),
+
+    /// Execute a sequence of edits in order.
+    Seq(Vec<Edit>),
+    /// Execute the provided edits in parallel.
+    All(Vec<Edit>),
+
+    /// Makes an edit dry.
+    ///
+    /// A dry edit only logs what operations would be performed, does not perform the I/O.
+    Dry(Box<Edit>),
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ApplyFailed;
+
+impl Edit {
+    #[expect(clippy::manual_async_fn)]
+    pub fn apply(self) -> impl Future<Output = Result<(), ApplyFailed>> + Send {
+        async {
+            match self {
+                Edit::NoOp => (),
+                Edit::Write(edit_path, content) => {
+                    tokio::fs::write(&edit_path.path, &content)
+                        .await
+                        .inspect_err(|err| error!("write to {edit_path:?} failed: {err:?}"))
+                        .map_err(|_| ApplyFailed)?;
+                }
+                Edit::Seq(vec) => {
+                    for edit in vec {
+                        Box::pin(edit.apply()).await?;
+                    }
+                }
+                Edit::All(vec) => {
+                    let mut set = JoinSet::new();
+                    for edit in vec {
+                        set.spawn(edit.apply());
+                    }
+                    while let Some(result) = set.try_join_next() {
+                        result.map_err(|_| ApplyFailed)??;
+                    }
+                }
+                Edit::Dry(edit) => edit.dry(),
+            }
+
+            Ok(())
+        }
+    }
+
+    pub fn dry(&self) {
+        match self {
+            Edit::NoOp => (),
+            Edit::Write(edit_path, content) => {
+                info!("{edit_path:?}: would write {:?} bytes", content.len());
+            }
+            Edit::Seq(edits) => edits.iter().for_each(Self::dry),
+            Edit::All(edits) => edits.iter().for_each(Self::dry),
+            Edit::Dry(edit) => edit.dry(),
+        }
+    }
+}
+
+impl fmt::Display for ApplyFailed {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("failed to apply some edits")
+    }
+}
+
+impl Error for ApplyFailed {}
+
+impl fmt::Debug for EditPath {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.path, f)
+    }
+}

crates/treehouse/src/vfs/empty.rs

@@ -1,9 +1,9 @@
-use super::{DirEntry, ReadFilesystem, VPath};
+use super::{Dir, DirEntry, VPath};
 
 #[derive(Debug)]
-pub struct EmptyFilesystem;
+pub struct EmptyEntry;
 
-impl ReadFilesystem for EmptyFilesystem {
+impl Dir for EmptyEntry {
     fn dir(&self, _path: &VPath) -> Vec<DirEntry> {
         vec![]
     }

crates/treehouse/src/vfs/file.rs

@@ -1,6 +1,6 @@
 use std::fmt;
 
-use super::{DirEntry, ReadFilesystem, VPath};
+use super::{DirEntry, Dir, VPath};
 
 pub struct BufferedFile {
     pub content: Vec<u8>,
@@ -12,7 +12,7 @@ impl BufferedFile {
     }
 }
 
-impl ReadFilesystem for BufferedFile {
+impl Dir for BufferedFile {
     fn dir(&self, _path: &VPath) -> Vec<DirEntry> {
         vec![]
     }

crates/treehouse/src/vfs/mem_dir.rs

@@ -1,29 +1,29 @@
 use std::{collections::HashMap, fmt};
 
-use super::{DirEntry, ReadFilesystem, VPath, VPathBuf};
+use super::{Dir, DirEntry, DynDir, EditPath, VPath, VPathBuf};
 
-pub struct MountPoints {
+pub struct MemDir {
-    mount_points: HashMap<String, Box<dyn ReadFilesystem>>,
+    mount_points: HashMap<String, DynDir>,
 }
 
 enum Resolved<'fs, 'path> {
     Root,
     MountPoint {
-        fs: &'fs dyn ReadFilesystem,
+        fs: &'fs dyn Dir,
         fs_path: &'path VPath,
         subpath: &'path VPath,
     },
     None,
 }
 
-impl MountPoints {
+impl MemDir {
     pub fn new() -> Self {
         Self {
             mount_points: HashMap::new(),
         }
     }
 
-    pub fn add(&mut self, path: &VPath, fs: Box<dyn ReadFilesystem>) {
+    pub fn add(&mut self, path: &VPath, dir: DynDir) {
         assert_eq!(
             path.depth(), 0,
             "path must be situated at root. MountPoints does not support nested paths, but you can nest MountPoints within other MountPoints"
@@ -31,7 +31,7 @@ impl MountPoints {
 
         assert!(
             self.mount_points
-                .insert(path.as_str().to_owned(), fs)
+                .insert(path.as_str().to_owned(), dir)
                 .is_none(),
             "duplicate mount point at {path:?}"
         );
@@ -57,13 +57,13 @@ impl MountPoints {
     }
 }
 
-impl Default for MountPoints {
+impl Default for MemDir {
     fn default() -> Self {
         Self::new()
     }
 }
 
-impl ReadFilesystem for MountPoints {
+impl Dir for MemDir {
     fn dir(&self, path: &VPath) -> Vec<DirEntry> {
         match self.resolve(path) {
             Resolved::Root => self
@@ -81,7 +81,7 @@ impl ReadFilesystem for MountPoints {
                 .dir(subpath)
                 .into_iter()
                 .map(|entry| DirEntry {
-                    path: fs_path.join(entry.path.as_str()),
+                    path: fs_path.join(&entry.path),
                 })
                 .collect(),
             Resolved::None => vec![],
@@ -120,9 +120,20 @@ impl ReadFilesystem for MountPoints {
             Resolved::Root | Resolved::None => None,
         }
     }
+
+    fn edit_path(&self, path: &VPath) -> Option<EditPath> {
+        match self.resolve(path) {
+            Resolved::MountPoint {
+                fs,
+                fs_path: _,
+                subpath,
+            } => fs.edit_path(subpath),
+            Resolved::Root | Resolved::None => None,
+        }
+    }
 }
 
-impl fmt::Debug for MountPoints {
+impl fmt::Debug for MemDir {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.write_str("MountPoints")
     }

crates/treehouse/src/vfs/overlay.rs

@@ -0,0 +1,52 @@
+use std::fmt;
+
+use super::{Dir, DirEntry, DynDir, EditPath, VPath, VPathBuf};
+
+pub struct Overlay {
+    base: DynDir,
+    overlay: DynDir,
+}
+
+impl Overlay {
+    pub fn new(base: DynDir, overlay: DynDir) -> Self {
+        Self { base, overlay }
+    }
+}
+
+impl Dir for Overlay {
+    fn dir(&self, path: &VPath) -> Vec<DirEntry> {
+        let mut dir = self.base.dir(path);
+        dir.append(&mut self.overlay.dir(path));
+        dir.sort();
+        dir.dedup();
+        dir
+    }
+
+    fn content(&self, path: &VPath) -> Option<Vec<u8>> {
+        self.overlay
+            .content(path)
+            .or_else(|| self.base.content(path))
+    }
+
+    fn content_version(&self, path: &VPath) -> Option<String> {
+        self.overlay
+            .content_version(path)
+            .or_else(|| self.base.content_version(path))
+    }
+
+    fn anchor(&self, path: &VPath) -> Option<VPathBuf> {
+        self.overlay.anchor(path).or_else(|| self.base.anchor(path))
+    }
+
+    fn edit_path(&self, path: &VPath) -> Option<EditPath> {
+        self.overlay
+            .edit_path(path)
+            .or_else(|| self.base.edit_path(path))
+    }
+}
+
+impl fmt::Debug for Overlay {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Overlay({:?}, {:?})", self.base, self.overlay)
+    }
+}

crates/treehouse/src/vfs/path.rs

@@ -0,0 +1,305 @@
+use std::{borrow::Borrow, error::Error, fmt, ops::Deref, str::FromStr};
+
+use serde::{Deserialize, Serialize};
+
+#[derive(PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct VPath {
+    path: str,
+}
+
+impl VPath {
+    pub const SEPARATOR_BYTE: u8 = b'/';
+    pub const SEPARATOR: char = Self::SEPARATOR_BYTE as char;
+    pub const ROOT: &Self = unsafe { Self::new_unchecked("") };
+
+    pub const fn try_new(s: &str) -> Result<&Self, InvalidPathError> {
+        if s.is_empty() {
+            return Ok(Self::ROOT);
+        }
+
+        let b = s.as_bytes();
+        if b[b.len() - 1] == Self::SEPARATOR_BYTE {
+            return Err(InvalidPathError::TrailingSlash);
+        }
+        if b[0] == Self::SEPARATOR_BYTE {
+            return Err(InvalidPathError::LeadingSlash);
+        }
+
+        Ok(unsafe { Self::new_unchecked(s) })
+    }
+
+    pub fn new(s: &str) -> &Self {
+        Self::try_new(s).expect("invalid path")
+    }
+
+    /// `const` version of [`new`][Self::new]. This has worse error messages, so prefer `new` whenever possible.
+    pub const fn new_const(s: &str) -> &Self {
+        match Self::try_new(s) {
+            Ok(p) => p,
+            Err(_) => panic!("invalid path"),
+        }
+    }
+
+    const unsafe fn new_unchecked(s: &str) -> &Self {
+        std::mem::transmute::<_, &Self>(s)
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.path.is_empty()
+    }
+
+    pub fn is_root(&self) -> bool {
+        self.is_empty()
+    }
+
+    pub fn join(&self, sub: &VPath) -> VPathBuf {
+        let mut buf = self.to_owned();
+        buf.push(sub);
+        buf
+    }
+
+    pub fn parent(&self) -> Option<&VPath> {
+        if self.is_root() {
+            None
+        } else if self.depth() == 0 {
+            Some(VPath::ROOT)
+        } else {
+            let (left, _right) = self
+                .path
+                .split_once(Self::SEPARATOR)
+                .expect("path with depth > 0 must have separators");
+            // SAFETY: We're splitting on a `/`, so there cannot be a trailing `/` in `left`.
+            Some(unsafe { VPath::new_unchecked(left) })
+        }
+    }
+
+    pub fn strip_prefix(&self, prefix: &VPath) -> Option<&Self> {
+        if self == prefix {
+            Some(VPath::ROOT)
+        } else {
+            self.path
+                .strip_prefix(&prefix.path)
+                .and_then(|p| p.strip_prefix(Self::SEPARATOR))
+                // SAFETY: If `self` starts with `prefix`, `p` will end up not being prefixed by `self`
+                // nor a leading slash.
+                .map(|p| unsafe { VPath::new_unchecked(p) })
+        }
+    }
+
+    pub fn depth(&self) -> usize {
+        self.path.chars().filter(|&c| c == Self::SEPARATOR).count()
+    }
+
+    pub fn segments(&self) -> impl Iterator<Item = &Self> {
+        self.as_str().split(Self::SEPARATOR).map(|s| unsafe {
+            // SAFETY: Since we're splitting on the separator, the path cannot start or end with it.
+            Self::new_unchecked(s)
+        })
+    }
+
+    pub fn rsegments(&self) -> impl Iterator<Item = &Self> {
+        self.as_str().rsplit(Self::SEPARATOR).map(|s| unsafe {
+            // SAFETY: Since we're splitting on the separator, the path cannot start or end with it.
+            Self::new_unchecked(s)
+        })
+    }
+
+    pub fn file_name(&self) -> Option<&str> {
+        self.rsegments().next().map(Self::as_str)
+    }
+
+    pub fn extension(&self) -> Option<&str> {
+        let file_name = self.file_name()?;
+        let (left, right) = file_name.rsplit_once('.')?;
+        if left.is_empty() {
+            None
+        } else {
+            Some(right)
+        }
+    }
+
+    pub fn with_extension(&self, extension: &str) -> VPathBuf {
+        let mut buf = self.to_owned();
+        buf.set_extension(extension);
+        buf
+    }
+
+    pub fn file_stem(&self) -> Option<&str> {
+        let file_name = self.file_name()?;
+        if let Some(extension) = self.extension() {
+            Some(&file_name[..file_name.len() - extension.len() - 1])
+        } else {
+            Some(file_name)
+        }
+    }
+
+    pub fn as_str(&self) -> &str {
+        &self.path
+    }
+}
+
+impl ToOwned for VPath {
+    type Owned = VPathBuf;
+
+    fn to_owned(&self) -> Self::Owned {
+        VPathBuf::from(self)
+    }
+}
+
+impl fmt::Debug for VPath {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.path)
+    }
+}
+
+impl fmt::Display for VPath {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.path)
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum InvalidPathError {
+    TrailingSlash,
+    LeadingSlash,
+}
+
+impl fmt::Display for InvalidPathError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            InvalidPathError::TrailingSlash => {
+                f.write_str("paths must not end with a trailing `/`")
+            }
+            InvalidPathError::LeadingSlash => {
+                f.write_str("paths are always absolute and must not start with `/`")
+            }
+        }
+    }
+}
+
+impl Error for InvalidPathError {}
+
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct VPathBuf {
+    path: String,
+}
+
+impl VPathBuf {
+    pub fn new(path: impl Into<String>) -> Self {
+        Self::try_new(path).expect("invalid path")
+    }
+
+    pub fn try_new(path: impl Into<String>) -> Result<Self, InvalidPathError> {
+        let path = path.into();
+        match VPath::try_new(&path) {
+            Ok(_) => Ok(Self { path }),
+            Err(e) => Err(e),
+        }
+    }
+
+    unsafe fn new_unchecked(path: String) -> Self {
+        Self { path }
+    }
+
+    pub fn push(&mut self, sub: &VPath) {
+        if !sub.is_empty() {
+            self.path.push('/');
+            self.path.push_str(&sub.path);
+        }
+    }
+
+    pub fn set_extension(&mut self, new_extension: &str) {
+        if let Some(existing) = self.extension() {
+            let mut chop_len = existing.len();
+            if new_extension.is_empty() {
+                chop_len += 1; // also chop off the `.`
+            }
+
+            let range = self.path.len() - chop_len..;
+            self.path.replace_range(range, new_extension);
+        }
+    }
+}
+
+impl Default for VPathBuf {
+    fn default() -> Self {
+        VPath::ROOT.to_owned()
+    }
+}
+
+impl Deref for VPathBuf {
+    type Target = VPath;
+
+    fn deref(&self) -> &Self::Target {
+        unsafe { VPath::new_unchecked(&self.path) }
+    }
+}
+
+impl fmt::Debug for VPathBuf {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.path)
+    }
+}
+
+impl fmt::Display for VPathBuf {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.path)
+    }
+}
+
+impl From<&VPath> for VPathBuf {
+    fn from(value: &VPath) -> Self {
+        unsafe { Self::new_unchecked(value.path.to_owned()) }
+    }
+}
+
+impl Borrow<VPath> for VPathBuf {
+    fn borrow(&self) -> &VPath {
+        self
+    }
+}
+
+impl<'de> Deserialize<'de> for VPathBuf {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        use serde::de;
+
+        struct Visitor;
+
+        impl de::Visitor<'_> for Visitor {
+            type Value = VPathBuf;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("virtual path")
+            }
+
+            fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                VPathBuf::try_new(v).map_err(de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
+    }
+}
+
+impl Serialize for VPathBuf {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serializer.serialize_str(self.as_str())
+    }
+}
+
+impl FromStr for VPathBuf {
+    type Err = InvalidPathError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Self::try_new(s)
+    }
+}

crates/treehouse/src/vfs/physical.rs

@@ -2,7 +2,7 @@ use std::path::{Path, PathBuf};
 
 use log::error;
 
-use super::{DirEntry, ReadFilesystem, VPath, VPathBuf};
+use super::{Dir, DirEntry, EditPath, VPath, VPathBuf};
 
 #[derive(Debug, Clone)]
 pub struct PhysicalDir {
@@ -15,7 +15,7 @@ impl PhysicalDir {
     }
 }
 
-impl ReadFilesystem for PhysicalDir {
+impl Dir for PhysicalDir {
     fn dir(&self, vpath: &VPath) -> Vec<DirEntry> {
         let physical = self.root.join(physical_path(vpath));
         if !physical.is_dir() {
@@ -68,6 +68,12 @@ impl ReadFilesystem for PhysicalDir {
             .inspect_err(|err| error!("{self:?} cannot read file at vpath {path:?}: {err:?}",))
             .ok()
     }
+
+    fn edit_path(&self, path: &VPath) -> Option<EditPath> {
+        Some(EditPath {
+            path: self.root.join(physical_path(path)),
+        })
+    }
 }
 
 fn physical_path(path: &VPath) -> &Path {

crates/treehouse/tests/it/vfs/cd.rs

@@ -1,33 +1,31 @@
-use treehouse::vfs::{
+use treehouse::vfs::{BufferedFile, Cd, Dir, DirEntry, MemDir, ToDynDir, VPath, VPathBuf};
-    BufferedFile, Cd, CdExt, DirEntry, MountPoints, ReadFilesystem, VPath, VPathBuf,
-};
 
 const HEWWO: &[u8] = b"hewwo :3";
 const FWOOFEE: &[u8] = b"fwoofee -w-";
 const BOOP: &[u8] = b"boop >w<";
 
-fn vfs() -> MountPoints {
+fn vfs() -> MemDir {
     let file1 = BufferedFile::new(HEWWO.to_vec());
     let file2 = BufferedFile::new(FWOOFEE.to_vec());
     let file3 = BufferedFile::new(BOOP.to_vec());
 
-    let mut innermost = MountPoints::new();
+    let mut innermost = MemDir::new();
-    innermost.add(VPath::new("file3.txt"), Box::new(file3));
+    innermost.add(VPath::new("file3.txt"), file3.to_dyn());
 
-    let mut inner = MountPoints::new();
+    let mut inner = MemDir::new();
-    inner.add(VPath::new("file1.txt"), Box::new(file1));
+    inner.add(VPath::new("file1.txt"), file1.to_dyn());
-    inner.add(VPath::new("file2.txt"), Box::new(file2));
+    inner.add(VPath::new("file2.txt"), file2.to_dyn());
-    inner.add(VPath::new("innermost"), Box::new(innermost));
+    inner.add(VPath::new("innermost"), innermost.to_dyn());
 
-    let mut vfs = MountPoints::new();
+    let mut vfs = MemDir::new();
-    vfs.add(VPath::new("inner"), Box::new(inner));
+    vfs.add(VPath::new("inner"), inner.to_dyn());
     vfs
 }
 
 #[test]
 fn dir1() {
     let outer = vfs();
-    let inner = Cd::new(&outer, VPathBuf::new("inner"));
+    let inner = Cd::new(outer, VPathBuf::new("inner"));
 
     let mut dir = inner.dir(VPath::ROOT);
     dir.sort();
@@ -49,23 +47,6 @@ fn dir1() {
 
 #[test]
 fn dir2() {
-    let outer = vfs();
-    let outer: &dyn ReadFilesystem = &outer;
-    let inner: &dyn ReadFilesystem = &outer.cd(VPathBuf::new("inner"));
-    let innermost = inner.cd(VPathBuf::new("innermost"));
-
-    let mut dir = innermost.dir(VPath::ROOT);
-    dir.sort();
-    assert_eq!(
-        dir,
-        vec![DirEntry {
-            path: VPathBuf::new("file3.txt"),
-        },]
-    );
-}
-
-#[test]
-fn dir3() {
     let outer = vfs();
     let innermost = Cd::new(&outer, VPathBuf::new("inner/innermost"));
 

crates/treehouse/tests/it/vfs/empty.rs

@@ -1,16 +1,16 @@
-use treehouse::vfs::{EmptyFilesystem, ReadFilesystem, VPath};
+use treehouse::vfs::{Dir, EmptyEntry, VPath};
 
 #[test]
 fn dir() {
-    assert!(EmptyFilesystem.dir(VPath::ROOT).is_empty());
+    assert!(EmptyEntry.dir(VPath::ROOT).is_empty());
 }
 
 #[test]
 fn content_version() {
-    assert!(EmptyFilesystem.content_version(VPath::ROOT).is_none());
+    assert!(EmptyEntry.content_version(VPath::ROOT).is_none());
 }
 
 #[test]
 fn content() {
-    assert!(EmptyFilesystem.content(VPath::ROOT).is_none());
+    assert!(EmptyEntry.content(VPath::ROOT).is_none());
 }

crates/treehouse/tests/it/vfs/file.rs

@@ -1,4 +1,4 @@
-use treehouse::vfs::{BufferedFile, ReadFilesystem, VPath};
+use treehouse::vfs::{BufferedFile, Dir, VPath};
 
 fn vfs() -> BufferedFile {
     BufferedFile::new(b"hewwo :3".to_vec())

crates/treehouse/tests/it/vfs/mount_points.rs

@@ -1,21 +1,23 @@
-use treehouse::vfs::{BufferedFile, DirEntry, MountPoints, ReadFilesystem, VPath, VPathBuf};
+use std::sync::Arc;
+
+use treehouse::vfs::{BufferedFile, Dir, DirEntry, MemDir, ToDynDir, VPath, VPathBuf};
 
 const HEWWO: &[u8] = b"hewwo :3";
 const FWOOFEE: &[u8] = b"fwoofee -w-";
 const BOOP: &[u8] = b"boop >w<";
 
-fn vfs() -> MountPoints {
+fn vfs() -> MemDir {
     let file1 = BufferedFile::new(HEWWO.to_vec());
     let file2 = BufferedFile::new(FWOOFEE.to_vec());
     let file3 = BufferedFile::new(BOOP.to_vec());
 
-    let mut inner = MountPoints::new();
+    let mut inner = MemDir::new();
-    inner.add(VPath::new("file3.txt"), Box::new(file3));
+    inner.add(VPath::new("file3.txt"), file3.to_dyn());
 
-    let mut vfs = MountPoints::new();
+    let mut vfs = MemDir::new();
-    vfs.add(VPath::new("file1.txt"), Box::new(file1));
+    vfs.add(VPath::new("file1.txt"), file1.to_dyn());
-    vfs.add(VPath::new("file2.txt"), Box::new(file2));
+    vfs.add(VPath::new("file2.txt"), file2.to_dyn());
-    vfs.add(VPath::new("inner"), Box::new(inner));
+    vfs.add(VPath::new("inner"), inner.to_dyn());
     vfs
 }
 

crates/treehouse/tests/it/vfs/physical.rs

@@ -1,6 +1,6 @@
 use std::path::Path;
 
-use treehouse::vfs::{DirEntry, PhysicalDir, ReadFilesystem, VPath, VPathBuf};
+use treehouse::vfs::{DirEntry, PhysicalDir, Dir, VPath, VPathBuf};
 
 fn vfs() -> PhysicalDir {
     let root = Path::new("tests/it/vfs_physical").to_path_buf();

treehouse.toml

@@ -57,7 +57,7 @@ description = "a place on the Internet I like to call home"
 
 [build.javascript]
 import_roots = [
-    { name = "treehouse", path = "static/js" },
+    { name = "treehouse", path = "" },
-    { name = "tairu", path = "static/js/components/tairu" },
+    { name = "tairu", path = "components/tairu" },
-    { name = "haku", path = "static/js/components/haku" },
+    { name = "haku", path = "components/haku" },
 ]