Load project file from VFS instead of through fs.

Fixes #320.

Previously, the root project file was loaded via methods on Project
(which do not know about the VFS) instead of through the VFS like
all other disk access.

This meant that Rojo was unable to build its own plugin because
there is no project file on the real disk, only in the VFS.

src/project.rs

@@ -111,8 +111,13 @@ impl Project {
     pub fn load_from_slice(
         contents: &[u8],
         project_file_location: &Path,
-    ) -> Result<Self, serde_json::Error> {
-        let mut project: Self = serde_json::from_slice(&contents)?;
+    ) -> Result<Self, ProjectError> {
+        let mut project: Self =
+            serde_json::from_slice(&contents).map_err(|source| Error::Json {
+                source,
+                path: project_file_location.to_owned(),
+            })?;
+
         project.file_location = project_file_location.to_path_buf();
         project.check_compatibility();
         Ok(project)

src/serve_session.rs

@@ -1,11 +1,14 @@
 use std::{
+    borrow::Cow,
     collections::HashSet,
+    io,
     path::{Path, PathBuf},
     sync::{Arc, Mutex, MutexGuard},
     time::Instant,
 };
 
 use crossbeam_channel::Sender;
+use memofs::IoResultExt;
 use memofs::Vfs;
 use rbx_dom_weak::RbxInstanceProperties;
 use thiserror::Error;
@@ -97,11 +100,23 @@ impl ServeSession {
 
         log::trace!("Starting new ServeSession at path {}", start_path.display());
 
-        log::debug!("Loading project file from {}", start_path.display());
-        let root_project =
-            Project::load_fuzzy(start_path)?.ok_or_else(|| ServeSessionError::NoProjectFound {
-                path: start_path.to_owned(),
-            })?;
+        let project_path;
+        if Project::is_project_file(start_path) {
+            project_path = Cow::Borrowed(start_path);
+        } else {
+            project_path = Cow::Owned(start_path.join("default.project.json"));
+        }
+
+        log::debug!("Loading project file from {}", project_path.display());
+
+        let root_project = match vfs.read(&project_path).with_not_found()? {
+            Some(contents) => Project::load_from_slice(&contents, &project_path)?,
+            None => {
+                return Err(ServeSessionError::NoProjectFound {
+                    path: project_path.to_path_buf(),
+                });
+            }
+        };
 
         let mut tree = RojoTree::new(InstancePropertiesWithMeta {
             properties: RbxInstanceProperties {
@@ -206,6 +221,12 @@ pub enum ServeSessionError {
     )]
     NoProjectFound { path: PathBuf },
 
+    #[error(transparent)]
+    Io {
+        #[from]
+        source: io::Error,
+    },
+
     #[error(transparent)]
     Project {
         #[from]

src/snapshot_middleware/error.rs

@@ -2,6 +2,8 @@ use std::{io, path::PathBuf};
 
 use thiserror::Error;
 
+use crate::project::ProjectError;
+
 #[derive(Debug, Error)]
 pub enum SnapshotError {
     #[error("file name had malformed Unicode")]
@@ -14,10 +16,7 @@ pub enum SnapshotError {
     },
 
     #[error("malformed project file at path {}", .path.display())]
-    MalformedProject {
-        source: serde_json::Error,
-        path: PathBuf,
-    },
+    MalformedProject { source: ProjectError, path: PathBuf },
 
     #[error("malformed .model.json file at path {}", .path.display())]
     MalformedModelJson {
@@ -62,7 +61,7 @@ impl SnapshotError {
         }
     }
 
-    pub(crate) fn malformed_project(source: serde_json::Error, path: impl Into<PathBuf>) -> Self {
+    pub(crate) fn malformed_project(source: ProjectError, path: impl Into<PathBuf>) -> Self {
         Self::MalformedProject {
             source,
             path: path.into(),