refactoring: remove dependency on SimpleFiles, make tree parsing multithreaded

crates/treehouse/src/tree/attributes.rs

@@ -2,6 +2,8 @@ use std::collections::HashMap;
 
 use serde::{Deserialize, Serialize};
 
+use crate::{state::FileId, vfs::VPathBuf};
+
 /// Top-level `%%` root attributes.
 #[derive(Debug, Default, Clone, PartialEq, Eq, Deserialize, Serialize)]
 pub struct RootAttributes {
@@ -118,7 +120,12 @@ pub enum Content {
     ///
     /// Note that `Link` branches must not contain any children. If a `Link` branch does contain
     /// children, an `attribute`-type error is raised.
-    Link(String),
+    Link(VPathBuf),
+
+    /// Valid link to another tree.
+    /// This replaces `Content::Link` during semantic analysis.
+    #[serde(skip)]
+    ResolvedLink(FileId),
 }
 
 #[derive(Debug, Default, Clone, PartialEq, Eq, Deserialize)]