Add --git-since option to rojo serve

- Add new GitFilter struct for tracking files changed since a Git reference
- Only sync changed (added/deleted/modified) files to Roblox Studio
- Files remain acknowledged once synced, even if content is reverted
- Add enhanced logging for debugging sync issues
- Force acknowledge project structure to prevent 'Cannot sync a model as a place' errors

CHANGELOG.md

@@ -30,6 +30,9 @@ Making a new release? Simply add the new header with the version and date undern
 -->
 
 ## Unreleased
+* Fixed a bug caused by having reference properties (such as `ObjectValue.Value`) that point to an Instance not included in syncback. ([#1179])
+
+[#1179]: https://github.com/rojo-rbx/rojo/pull/1179
 
 ## [7.7.0-rc.1] (November 27th, 2025)
 

Cargo.lock

@@ -1313,7 +1313,7 @@ checksum = "f52b00d39961fc5b2736ea853c9cc86238e165017a493d1d5c8eac6bdc4cc273"
 
 [[package]]
 name = "memofs"
-version = "0.3.0"
+version = "0.3.1"
 dependencies = [
  "crossbeam-channel",
  "fs-err",

Cargo.toml

@@ -46,7 +46,7 @@ name = "build"
 harness = false
 
 [dependencies]
-memofs = { version = "0.3.0", path = "crates/memofs" }
+memofs = { version = "0.3.1", path = "crates/memofs" }
 
 # These dependencies can be uncommented when working on rbx-dom simultaneously
 # rbx_binary = { path = "../rbx-dom/rbx_binary", features = [

crates/memofs/CHANGELOG.md

@@ -1,6 +1,8 @@
 # memofs Changelog
 
 ## Unreleased Changes
+
+## 0.3.1 (2025-11-27)
 * Added `Vfs::exists`. [#1169]
 * Added `create_dir` and `create_dir_all` to allow creating directories. [#937]
 

crates/memofs/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "memofs"
 description = "Virtual filesystem with configurable backends."
-version = "0.3.0"
+version = "0.3.1"
 authors = [
     "Lucien Greathouse <me@lpghatguy.com>",
     "Micah Reid <git@dekkonot.com>",

crates/memofs/src/noop_backend.rs

@@ -31,17 +31,11 @@ impl VfsBackend for NoopBackend {
     }
 
     fn create_dir(&mut self, _path: &Path) -> io::Result<()> {
-        Err(io::Error::new(
+        Err(io::Error::other("NoopBackend doesn't do anything"))
-            io::ErrorKind::Other,
-            "NoopBackend doesn't do anything",
-        ))
     }
 
     fn create_dir_all(&mut self, _path: &Path) -> io::Result<()> {
-        Err(io::Error::new(
+        Err(io::Error::other("NoopBackend doesn't do anything"))
-            io::ErrorKind::Other,
-            "NoopBackend doesn't do anything",
-        ))
     }
 
     fn remove_file(&mut self, _path: &Path) -> io::Result<()> {

rojo-test/syncback-test-snapshots/end_to_end__rojo_test__syncback_util__ref_properties_pruned-stdout.snap

@@ -0,0 +1,7 @@
+---
+source: tests/rojo_test/syncback_util.rs
+expression: "String::from_utf8_lossy(&output.stdout)"
+---
+Writing src/Pointer1.model.json
+Writing src/Pointer2.model.json
+Writing src/Pointer3.model.json

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__ref_properties_pruned-src__Pointer1.model.json.snap

@@ -0,0 +1,7 @@
+---
+source: tests/tests/syncback.rs
+expression: src/Pointer1.model.json
+---
+{
+  "className": "ObjectValue"
+}

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__ref_properties_pruned-src__Pointer2.model.json.snap

@@ -0,0 +1,7 @@
+---
+source: tests/tests/syncback.rs
+expression: src/Pointer2.model.json
+---
+{
+  "className": "ObjectValue"
+}

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__ref_properties_pruned-src__Pointer3.model.json.snap

@@ -0,0 +1,7 @@
+---
+source: tests/tests/syncback.rs
+expression: src/Pointer3.model.json
+---
+{
+  "className": "ObjectValue"
+}

rojo-test/syncback-tests/ref_properties_pruned/input-project/default.project.json

@@ -0,0 +1,9 @@
+{
+  "name": "ref_properties_pruned",
+  "tree": {
+    "$className": "DataModel",
+    "ServerScriptService": {
+      "$path": "src"
+    }
+  }
+}

src/change_processor.rs

@@ -9,6 +9,7 @@ use memofs::{IoResultExt, Vfs, VfsEvent};
 use rbx_dom_weak::types::{Ref, Variant};
 
 use crate::{
+    git::SharedGitFilter,
     message_queue::MessageQueue,
     snapshot::{
         apply_patch_set, compute_patch_set, AppliedPatchSet, InstigatingSource, PatchSet, RojoTree,
@@ -46,11 +47,15 @@ pub struct ChangeProcessor {
 impl ChangeProcessor {
     /// Spin up the ChangeProcessor, connecting it to the given tree, VFS, and
     /// outbound message queue.
+    ///
+    /// If `git_filter` is provided, it will be refreshed on every VFS event
+    /// to ensure newly changed files are acknowledged.
     pub fn start(
         tree: Arc<Mutex<RojoTree>>,
         vfs: Arc<Vfs>,
         message_queue: Arc<MessageQueue<AppliedPatchSet>>,
         tree_mutation_receiver: Receiver<PatchSet>,
+        git_filter: Option<SharedGitFilter>,
     ) -> Self {
         let (shutdown_sender, shutdown_receiver) = crossbeam_channel::bounded(1);
         let vfs_receiver = vfs.event_receiver();
@@ -58,6 +63,7 @@ impl ChangeProcessor {
             tree,
             vfs,
             message_queue,
+            git_filter,
         };
 
         let job_thread = jod_thread::Builder::new()
@@ -111,12 +117,24 @@ struct JobThreadContext {
     /// Whenever changes are applied to the DOM, we should push those changes
     /// into this message queue to inform any connected clients.
     message_queue: Arc<MessageQueue<AppliedPatchSet>>,
+
+    /// Optional Git filter for --git-since mode. When set, will be refreshed
+    /// on every VFS event to ensure newly changed files are acknowledged.
+    git_filter: Option<SharedGitFilter>,
 }
 
 impl JobThreadContext {
     fn handle_vfs_event(&self, event: VfsEvent) {
         log::trace!("Vfs event: {:?}", event);
 
+        // If we have a git filter, refresh it to pick up any new changes.
+        // This ensures that files modified during the session will be acknowledged.
+        if let Some(ref git_filter) = self.git_filter {
+            if let Err(err) = git_filter.refresh() {
+                log::warn!("Failed to refresh git filter: {:?}", err);
+            }
+        }
+
         // Update the VFS immediately with the event.
         self.vfs
             .commit_event(&event)
@@ -151,6 +169,19 @@ impl JobThreadContext {
                     }
                 };
 
+                if affected_ids.is_empty() {
+                    log::debug!(
+                        "No instances found for path {} or any of its ancestors",
+                        path.display()
+                    );
+                } else {
+                    log::debug!(
+                        "Found {} affected instances for path {}",
+                        affected_ids.len(),
+                        path.display()
+                    );
+                }
+
                 for id in affected_ids {
                     if let Some(patch) = compute_and_apply_changes(&mut tree, &self.vfs, id) {
                         if !patch.is_empty() {

src/cli/build.rs

@@ -81,7 +81,7 @@ impl BuildCommand {
         let vfs = Vfs::new_default();
         vfs.set_watch_enabled(self.watch);
 
-        let session = ServeSession::new(vfs, project_path)?;
+        let session = ServeSession::new(vfs, project_path, None)?;
         let mut cursor = session.message_queue().cursor();
 
         write_model(&session, &output_path, output_kind)?;

src/cli/plugin.rs

@@ -54,7 +54,7 @@ fn initialize_plugin() -> anyhow::Result<ServeSession> {
     in_memory_fs.load_snapshot("/plugin", plugin_snapshot)?;
 
     let vfs = Vfs::new(in_memory_fs);
-    Ok(ServeSession::new(vfs, "/plugin")?)
+    Ok(ServeSession::new(vfs, "/plugin", None)?)
 }
 
 fn install_plugin() -> anyhow::Result<()> {

src/cli/serve.rs

@@ -9,7 +9,7 @@ use clap::Parser;
 use memofs::Vfs;
 use termcolor::{BufferWriter, Color, ColorChoice, ColorSpec, WriteColor};
 
-use crate::{serve_session::ServeSession, web::LiveServer};
+use crate::{git::GitFilter, serve_session::ServeSession, web::LiveServer};
 
 use super::{resolve_path, GlobalOptions};
 
@@ -31,6 +31,19 @@ pub struct ServeCommand {
     /// it has none.
     #[clap(long)]
     pub port: Option<u16>,
+
+    /// Only sync files that have changed since the given Git reference.
+    ///
+    /// When this option is set, Rojo will only include files that have been
+    /// modified, added, or are untracked since the specified Git reference
+    /// (e.g., "HEAD", "main", a commit hash). This is useful for working with
+    /// large projects where you only want to sync your local changes.
+    ///
+    /// Scripts that have not changed will still be acknowledged if modified
+    /// during the session, and all synced instances will have
+    /// ignoreUnknownInstances set to true to preserve descendants in Studio.
+    #[clap(long, value_name = "REF")]
+    pub git_since: Option<String>,
 }
 
 impl ServeCommand {
@@ -39,7 +52,19 @@ impl ServeCommand {
 
         let vfs = Vfs::new_default();
 
-        let session = Arc::new(ServeSession::new(vfs, project_path)?);
+        // Set up Git filter if --git-since was specified
+        let git_filter = if let Some(ref base_ref) = self.git_since {
+            let repo_root = GitFilter::find_repo_root(&project_path)?;
+            log::info!(
+                "Git filter enabled: only syncing files changed since '{}'",
+                base_ref
+            );
+            Some(Arc::new(GitFilter::new(repo_root, base_ref.clone(), &project_path)?))
+        } else {
+            None
+        };
+
+        let session = Arc::new(ServeSession::new(vfs, project_path, git_filter)?);
 
         let ip = self
             .address
@@ -53,17 +78,25 @@ impl ServeCommand {
 
         let server = LiveServer::new(session);
 
-        let _ = show_start_message(ip, port, global.color.into());
+        let _ = show_start_message(ip, port, self.git_since.as_deref(), global.color.into());
         server.start((ip, port).into());
 
         Ok(())
     }
 }
 
-fn show_start_message(bind_address: IpAddr, port: u16, color: ColorChoice) -> io::Result<()> {
+fn show_start_message(
+    bind_address: IpAddr,
+    port: u16,
+    git_since: Option<&str>,
+    color: ColorChoice,
+) -> io::Result<()> {
     let mut green = ColorSpec::new();
     green.set_fg(Some(Color::Green)).set_bold(true);
 
+    let mut yellow = ColorSpec::new();
+    yellow.set_fg(Some(Color::Yellow)).set_bold(true);
+
     let writer = BufferWriter::stdout(color);
     let mut buffer = writer.buffer();
 
@@ -84,6 +117,13 @@ fn show_start_message(bind_address: IpAddr, port: u16, color: ColorChoice) -> io
     buffer.set_color(&green)?;
     writeln!(&mut buffer, "{}", port)?;
 
+    if let Some(base_ref) = git_since {
+        buffer.set_color(&ColorSpec::new())?;
+        write!(&mut buffer, "  Mode:    ")?;
+        buffer.set_color(&yellow)?;
+        writeln!(&mut buffer, "git-since ({})", base_ref)?;
+    }
+
     writeln!(&mut buffer)?;
 
     buffer.set_color(&ColorSpec::new())?;

src/cli/sourcemap.rs

@@ -76,7 +76,7 @@ impl SourcemapCommand {
         let vfs = Vfs::new_default();
         vfs.set_watch_enabled(self.watch);
 
-        let session = ServeSession::new(vfs, project_path)?;
+        let session = ServeSession::new(vfs, project_path, None)?;
         let mut cursor = session.message_queue().cursor();
 
         let filter = if self.include_non_scripts {

src/cli/syncback.rs

@@ -73,7 +73,7 @@ impl SyncbackCommand {
         vfs.set_watch_enabled(false);
 
         let project_start_timer = Instant::now();
-        let session_old = ServeSession::new(vfs, path_old.clone())?;
+        let session_old = ServeSession::new(vfs, path_old.clone(), None)?;
         log::debug!(
             "Finished opening project in {:0.02}s",
             project_start_timer.elapsed().as_secs_f32()

src/cli/upload.rs

@@ -42,7 +42,7 @@ impl UploadCommand {
 
         let vfs = Vfs::new_default();
 
-        let session = ServeSession::new(vfs, project_path)?;
+        let session = ServeSession::new(vfs, project_path, None)?;
 
         let tree = session.tree();
         let inner_tree = tree.inner();

src/git.rs

@@ -0,0 +1,380 @@
+//! Git integration for filtering files based on changes since a reference.
+
+use std::{
+    collections::HashSet,
+    path::{Path, PathBuf},
+    process::Command,
+    sync::{Arc, RwLock},
+};
+
+use anyhow::{bail, Context};
+
+/// A filter that tracks which files have been changed since a Git reference.
+///
+/// When active, only files that have been modified, added, or deleted according
+/// to Git will be "acknowledged" and synced to Studio. This allows users to
+/// work with large projects where they only want to sync their local changes.
+///
+/// Once a file is acknowledged (either initially or during the session), it
+/// stays acknowledged for the entire session. This prevents files from being
+/// deleted in Studio if their content is reverted to match the git reference.
+#[derive(Debug)]
+pub struct GitFilter {
+    /// The Git repository root directory.
+    repo_root: PathBuf,
+
+    /// The Git reference to compare against (e.g., "HEAD", "main", a commit hash).
+    base_ref: String,
+
+    /// Cache of paths that are currently different from the base ref according to git.
+    /// This is refreshed on every VFS event.
+    git_changed_paths: RwLock<HashSet<PathBuf>>,
+
+    /// Paths that have been acknowledged at any point during this session.
+    /// Once a path is added here, it stays acknowledged forever (for this session).
+    /// This prevents files from being deleted if their content is reverted.
+    session_acknowledged_paths: RwLock<HashSet<PathBuf>>,
+}
+
+impl GitFilter {
+    /// Creates a new GitFilter for the given repository root and base reference.
+    ///
+    /// The `repo_root` should be the root of the Git repository (where .git is located).
+    /// The `base_ref` is the Git reference to compare against (e.g., "HEAD", "main").
+    /// The `project_path` is the path to the project being served - it will always be
+    /// acknowledged regardless of git status to ensure the project structure exists.
+    pub fn new(repo_root: PathBuf, base_ref: String, project_path: &Path) -> anyhow::Result<Self> {
+        let filter = Self {
+            repo_root,
+            base_ref,
+            git_changed_paths: RwLock::new(HashSet::new()),
+            session_acknowledged_paths: RwLock::new(HashSet::new()),
+        };
+
+        // Always acknowledge the project path and its directory so the project
+        // structure exists even when there are no git changes
+        filter.acknowledge_project_path(project_path);
+
+        // Initial refresh to populate the cache with git changes
+        filter.refresh()?;
+
+        Ok(filter)
+    }
+
+    /// Acknowledges the project path and its containing directory.
+    /// This ensures the project structure always exists regardless of git status.
+    fn acknowledge_project_path(&self, project_path: &Path) {
+        let mut session = self.session_acknowledged_paths.write().unwrap();
+
+        // Acknowledge the project path itself (might be a directory or .project.json file)
+        let canonical = project_path.canonicalize().unwrap_or_else(|_| project_path.to_path_buf());
+        session.insert(canonical.clone());
+
+        // Acknowledge all ancestor directories
+        let mut current = canonical.parent();
+        while let Some(parent) = current {
+            session.insert(parent.to_path_buf());
+            current = parent.parent();
+        }
+
+        // If it's a directory, also acknowledge default.project.json inside it
+        if project_path.is_dir() {
+            for name in &["default.project.json", "default.project.jsonc"] {
+                let project_file = project_path.join(name);
+                if let Ok(canonical_file) = project_file.canonicalize() {
+                    session.insert(canonical_file);
+                } else {
+                    session.insert(project_file);
+                }
+            }
+        }
+
+        // If it's a .project.json file, also acknowledge its parent directory
+        if let Some(parent) = project_path.parent() {
+            let parent_canonical = parent.canonicalize().unwrap_or_else(|_| parent.to_path_buf());
+            session.insert(parent_canonical);
+        }
+
+        log::debug!(
+            "GitFilter: acknowledged project path {} ({} paths total)",
+            project_path.display(),
+            session.len()
+        );
+    }
+
+    /// Finds the Git repository root for the given path.
+    pub fn find_repo_root(path: &Path) -> anyhow::Result<PathBuf> {
+        let output = Command::new("git")
+            .args(["rev-parse", "--show-toplevel"])
+            .current_dir(path)
+            .output()
+            .context("Failed to execute git rev-parse")?;
+
+        if !output.status.success() {
+            let stderr = String::from_utf8_lossy(&output.stderr);
+            bail!("Failed to find Git repository root: {}", stderr.trim());
+        }
+
+        let root = String::from_utf8_lossy(&output.stdout)
+            .trim()
+            .to_string();
+
+        Ok(PathBuf::from(root))
+    }
+
+    /// Refreshes the cache of acknowledged paths by querying Git.
+    ///
+    /// This should be called when files change to ensure newly modified files
+    /// are properly acknowledged. Once a path is acknowledged, it stays
+    /// acknowledged for the entire session (even if the file is reverted).
+    pub fn refresh(&self) -> anyhow::Result<()> {
+        let mut git_changed = HashSet::new();
+
+        // Get files changed since the base ref (modified, added, deleted)
+        let diff_output = Command::new("git")
+            .args(["diff", "--name-only", &self.base_ref])
+            .current_dir(&self.repo_root)
+            .output()
+            .context("Failed to execute git diff")?;
+
+        if !diff_output.status.success() {
+            let stderr = String::from_utf8_lossy(&diff_output.stderr);
+            bail!("git diff failed: {}", stderr.trim());
+        }
+
+        let diff_files = String::from_utf8_lossy(&diff_output.stdout);
+        let diff_count = diff_files.lines().filter(|l| !l.is_empty()).count();
+        if diff_count > 0 {
+            log::debug!("git diff found {} changed files", diff_count);
+        }
+        for line in diff_files.lines() {
+            if !line.is_empty() {
+                let path = self.repo_root.join(line);
+                log::trace!("git diff: acknowledging {}", path.display());
+                self.acknowledge_path(&path, &mut git_changed);
+            }
+        }
+
+        // Get untracked files (new files not yet committed)
+        let untracked_output = Command::new("git")
+            .args(["ls-files", "--others", "--exclude-standard"])
+            .current_dir(&self.repo_root)
+            .output()
+            .context("Failed to execute git ls-files")?;
+
+        if !untracked_output.status.success() {
+            let stderr = String::from_utf8_lossy(&untracked_output.stderr);
+            bail!("git ls-files failed: {}", stderr.trim());
+        }
+
+        let untracked_files = String::from_utf8_lossy(&untracked_output.stdout);
+        for line in untracked_files.lines() {
+            if !line.is_empty() {
+                let path = self.repo_root.join(line);
+                self.acknowledge_path(&path, &mut git_changed);
+            }
+        }
+
+        // Get staged files (files added to index but not yet committed)
+        let staged_output = Command::new("git")
+            .args(["diff", "--name-only", "--cached", &self.base_ref])
+            .current_dir(&self.repo_root)
+            .output()
+            .context("Failed to execute git diff --cached")?;
+
+        if staged_output.status.success() {
+            let staged_files = String::from_utf8_lossy(&staged_output.stdout);
+            for line in staged_files.lines() {
+                if !line.is_empty() {
+                    let path = self.repo_root.join(line);
+                    self.acknowledge_path(&path, &mut git_changed);
+                }
+            }
+        }
+
+        // Update the git changed paths cache
+        {
+            let mut cache = self.git_changed_paths.write().unwrap();
+            *cache = git_changed.clone();
+        }
+
+        // Merge newly changed paths into session acknowledged paths
+        // Once acknowledged, a path stays acknowledged for the entire session
+        {
+            let mut session = self.session_acknowledged_paths.write().unwrap();
+            for path in git_changed {
+                session.insert(path);
+            }
+            log::debug!(
+                "GitFilter refreshed: {} paths acknowledged in session",
+                session.len()
+            );
+        }
+
+        Ok(())
+    }
+
+    /// Acknowledges a path and all its ancestors, plus associated meta files.
+    fn acknowledge_path(&self, path: &Path, acknowledged: &mut HashSet<PathBuf>) {
+        // Canonicalize the path if possible, otherwise use as-is
+        let path = path.canonicalize().unwrap_or_else(|_| path.to_path_buf());
+
+        // Add the path itself
+        acknowledged.insert(path.clone());
+
+        // Add all ancestor directories
+        let mut current = path.parent();
+        while let Some(parent) = current {
+            acknowledged.insert(parent.to_path_buf());
+            current = parent.parent();
+        }
+
+        // Add associated meta files
+        self.acknowledge_meta_files(&path, acknowledged);
+    }
+
+    /// Acknowledges associated meta files for a given path.
+    fn acknowledge_meta_files(&self, path: &Path, acknowledged: &mut HashSet<PathBuf>) {
+        if let Some(file_name) = path.file_name().and_then(|n| n.to_str()) {
+            if let Some(parent) = path.parent() {
+                // For a file like "foo.lua", also acknowledge "foo.meta.json"
+                // Strip known extensions to get the base name
+                let base_name = strip_lua_extension(file_name);
+
+                let meta_path = parent.join(format!("{}.meta.json", base_name));
+                if let Ok(canonical) = meta_path.canonicalize() {
+                    acknowledged.insert(canonical);
+                } else {
+                    acknowledged.insert(meta_path);
+                }
+
+                // For init files, also acknowledge "init.meta.json" in the same directory
+                if file_name.starts_with("init.") {
+                    let init_meta = parent.join("init.meta.json");
+                    if let Ok(canonical) = init_meta.canonicalize() {
+                        acknowledged.insert(canonical);
+                    } else {
+                        acknowledged.insert(init_meta);
+                    }
+                }
+            }
+        }
+    }
+
+    /// Checks if a path is acknowledged (should be synced).
+    ///
+    /// Returns `true` if the path or any of its descendants have been changed
+    /// at any point during this session. Once a file is acknowledged, it stays
+    /// acknowledged even if its content is reverted to match the git reference.
+    pub fn is_acknowledged(&self, path: &Path) -> bool {
+        let session = self.session_acknowledged_paths.read().unwrap();
+
+        // Try to canonicalize the path
+        let canonical = path.canonicalize().unwrap_or_else(|_| path.to_path_buf());
+
+        // Check if this exact path is acknowledged
+        if session.contains(&canonical) {
+            log::trace!("Path {} is directly acknowledged", path.display());
+            return true;
+        }
+
+        // Also check without canonicalization in case of path differences
+        if session.contains(path) {
+            log::trace!("Path {} is acknowledged (non-canonical)", path.display());
+            return true;
+        }
+
+        // For directories, check if any descendant is acknowledged
+        // This is done by checking if any acknowledged path starts with this path
+        for acknowledged in session.iter() {
+            if acknowledged.starts_with(&canonical) {
+                log::trace!(
+                    "Path {} has acknowledged descendant {}",
+                    path.display(),
+                    acknowledged.display()
+                );
+                return true;
+            }
+            // Also check non-canonical
+            if acknowledged.starts_with(path) {
+                log::trace!(
+                    "Path {} has acknowledged descendant {} (non-canonical)",
+                    path.display(),
+                    acknowledged.display()
+                );
+                return true;
+            }
+        }
+
+        log::trace!(
+            "Path {} is NOT acknowledged (canonical: {})",
+            path.display(),
+            canonical.display()
+        );
+        false
+    }
+
+    /// Returns the base reference being compared against.
+    pub fn base_ref(&self) -> &str {
+        &self.base_ref
+    }
+
+    /// Returns the repository root path.
+    pub fn repo_root(&self) -> &Path {
+        &self.repo_root
+    }
+
+    /// Explicitly acknowledges a path and all its ancestors.
+    /// This is useful for ensuring certain paths are always synced regardless of git status.
+    pub fn force_acknowledge(&self, path: &Path) {
+        let mut acknowledged = HashSet::new();
+        self.acknowledge_path(path, &mut acknowledged);
+
+        let mut session = self.session_acknowledged_paths.write().unwrap();
+        for p in acknowledged {
+            session.insert(p);
+        }
+    }
+}
+
+/// Strips Lua-related extensions from a file name to get the base name.
+fn strip_lua_extension(file_name: &str) -> &str {
+    const EXTENSIONS: &[&str] = &[
+        ".server.luau",
+        ".server.lua",
+        ".client.luau",
+        ".client.lua",
+        ".luau",
+        ".lua",
+    ];
+
+    for ext in EXTENSIONS {
+        if let Some(base) = file_name.strip_suffix(ext) {
+            return base;
+        }
+    }
+
+    // If no Lua extension, try to strip the regular extension
+    file_name
+        .rsplit_once('.')
+        .map(|(base, _)| base)
+        .unwrap_or(file_name)
+}
+
+/// A wrapper around GitFilter that can be shared across threads.
+pub type SharedGitFilter = Arc<GitFilter>;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_strip_lua_extension() {
+        assert_eq!(strip_lua_extension("foo.server.lua"), "foo");
+        assert_eq!(strip_lua_extension("foo.client.luau"), "foo");
+        assert_eq!(strip_lua_extension("foo.lua"), "foo");
+        assert_eq!(strip_lua_extension("init.server.lua"), "init");
+        assert_eq!(strip_lua_extension("bar.txt"), "bar");
+        assert_eq!(strip_lua_extension("noextension"), "noextension");
+    }
+}

src/lib.rs

@@ -9,6 +9,7 @@ mod tree_view;
 
 mod auth_cookie;
 mod change_processor;
+mod git;
 mod glob;
 mod json;
 mod lua_ast;
@@ -28,6 +29,7 @@ mod web;
 
 // TODO: Work out what we should expose publicly
 
+pub use git::{GitFilter, SharedGitFilter};
 pub use project::*;
 pub use rojo_ref::*;
 pub use session_id::SessionId;

src/serve_session.rs

@@ -13,6 +13,7 @@ use thiserror::Error;
 
 use crate::{
     change_processor::ChangeProcessor,
+    git::SharedGitFilter,
     message_queue::MessageQueue,
     project::{Project, ProjectError},
     session_id::SessionId,
@@ -94,7 +95,14 @@ impl ServeSession {
     /// The project file is expected to be loaded out-of-band since it's
     /// currently loaded from the filesystem directly instead of through the
     /// in-memory filesystem layer.
-    pub fn new<P: AsRef<Path>>(vfs: Vfs, start_path: P) -> Result<Self, ServeSessionError> {
+    ///
+    /// If `git_filter` is provided, only files that have changed since the
+    /// specified Git reference will be synced.
+    pub fn new<P: AsRef<Path>>(
+        vfs: Vfs,
+        start_path: P,
+        git_filter: Option<SharedGitFilter>,
+    ) -> Result<Self, ServeSessionError> {
         let start_path = start_path.as_ref();
         let start_time = Instant::now();
 
@@ -102,12 +110,28 @@ impl ServeSession {
 
         let root_project = Project::load_initial_project(&vfs, start_path)?;
 
+        // If git filter is active, ensure the project file location is acknowledged
+        // This is necessary so the project structure exists even with no git changes
+        if let Some(ref filter) = git_filter {
+            filter.force_acknowledge(start_path);
+            filter.force_acknowledge(&root_project.file_location);
+            filter.force_acknowledge(root_project.folder_location());
+            log::debug!(
+                "Force acknowledged project at {}",
+                root_project.file_location.display()
+            );
+        }
+
         let mut tree = RojoTree::new(InstanceSnapshot::new());
 
         let root_id = tree.get_root_id();
 
-        let instance_context =
+        let instance_context = match &git_filter {
-            InstanceContext::with_emit_legacy_scripts(root_project.emit_legacy_scripts);
+            Some(filter) => {
+                InstanceContext::with_git_filter(root_project.emit_legacy_scripts, Arc::clone(filter))
+            }
+            None => InstanceContext::with_emit_legacy_scripts(root_project.emit_legacy_scripts),
+        };
 
         log::trace!("Generating snapshot of instances from VFS");
         let snapshot = snapshot_from_vfs(&instance_context, &vfs, start_path)?;
@@ -133,6 +157,7 @@ impl ServeSession {
             Arc::clone(&vfs),
             Arc::clone(&message_queue),
             tree_mutation_receiver,
+            git_filter,
         );
 
         Ok(Self {

src/snapshot/metadata.rs

@@ -8,6 +8,7 @@ use anyhow::Context;
 use serde::{Deserialize, Serialize};
 
 use crate::{
+    git::SharedGitFilter,
     glob::Glob,
     path_serializer,
     project::ProjectNode,
@@ -138,13 +139,27 @@ impl Default for InstanceMetadata {
     }
 }
 
-#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct InstanceContext {
     #[serde(skip_serializing_if = "Vec::is_empty")]
     pub path_ignore_rules: Arc<Vec<PathIgnoreRule>>,
     pub emit_legacy_scripts: bool,
     #[serde(skip_serializing_if = "Vec::is_empty")]
     pub sync_rules: Vec<SyncRule>,
+    /// Optional Git filter for --git-since mode. When set, only files that have
+    /// changed since the specified Git reference will be synced.
+    #[serde(skip)]
+    pub git_filter: Option<SharedGitFilter>,
+}
+
+impl PartialEq for InstanceContext {
+    fn eq(&self, other: &Self) -> bool {
+        // Note: git_filter is intentionally excluded from comparison
+        // since it's runtime state, not configuration
+        self.path_ignore_rules == other.path_ignore_rules
+            && self.emit_legacy_scripts == other.emit_legacy_scripts
+            && self.sync_rules == other.sync_rules
+    }
 }
 
 impl InstanceContext {
@@ -153,6 +168,7 @@ impl InstanceContext {
             path_ignore_rules: Arc::new(Vec::new()),
             emit_legacy_scripts: emit_legacy_scripts_default().unwrap(),
             sync_rules: Vec::new(),
+            git_filter: None,
         }
     }
 
@@ -165,6 +181,36 @@ impl InstanceContext {
         }
     }
 
+    /// Creates a new InstanceContext with a Git filter for --git-since mode.
+    pub fn with_git_filter(
+        emit_legacy_scripts: Option<bool>,
+        git_filter: SharedGitFilter,
+    ) -> Self {
+        Self {
+            git_filter: Some(git_filter),
+            ..Self::with_emit_legacy_scripts(emit_legacy_scripts)
+        }
+    }
+
+    /// Sets the Git filter for this context.
+    pub fn set_git_filter(&mut self, git_filter: Option<SharedGitFilter>) {
+        self.git_filter = git_filter;
+    }
+
+    /// Returns true if the given path should be acknowledged (synced).
+    /// If no git filter is set, all paths are acknowledged.
+    pub fn is_path_acknowledged(&self, path: &Path) -> bool {
+        match &self.git_filter {
+            Some(filter) => filter.is_acknowledged(path),
+            None => true,
+        }
+    }
+
+    /// Returns true if a git filter is active.
+    pub fn has_git_filter(&self) -> bool {
+        self.git_filter.is_some()
+    }
+
     /// Extend the list of ignore rules in the context with the given new rules.
     pub fn add_path_ignore_rules<I>(&mut self, new_rules: I)
     where

src/snapshot_middleware/mod.rs

@@ -61,6 +61,10 @@ pub use self::{
 /// This will inspect the path and find the appropriate middleware for it,
 /// taking user-written rules into account. Then, it will attempt to convert
 /// the path into an InstanceSnapshot using that middleware.
+///
+/// If a git filter is active in the context and the path is not acknowledged
+/// (i.e., the file hasn't changed since the base git reference), this function
+/// returns `Ok(None)` to skip syncing that file.
 #[profiling::function]
 pub fn snapshot_from_vfs(
     context: &InstanceContext,
@@ -72,6 +76,16 @@ pub fn snapshot_from_vfs(
         None => return Ok(None),
     };
 
+    // Check if this path is acknowledged by the git filter.
+    // If not, skip this path entirely.
+    if !context.is_path_acknowledged(path) {
+        log::trace!(
+            "Skipping path {} (not acknowledged by git filter)",
+            path.display()
+        );
+        return Ok(None);
+    }
+
     if meta.is_dir() {
         let (middleware, dir_name, init_path) = get_dir_middleware(vfs, path)?;
         // TODO: Support user defined init paths
@@ -213,6 +227,10 @@ pub enum Middleware {
 impl Middleware {
     /// Creates a snapshot for the given path from the Middleware with
     /// the provided name.
+    ///
+    /// When a git filter is active in the context, `ignore_unknown_instances`
+    /// will be set to `true` on all generated snapshots to preserve descendants
+    /// in Studio that are not tracked by Rojo.
     fn snapshot(
         &self,
         context: &InstanceContext,
@@ -262,6 +280,14 @@ impl Middleware {
         };
         if let Ok(Some(ref mut snapshot)) = output {
             snapshot.metadata.middleware = Some(*self);
+
+            // When git filter is active, force ignore_unknown_instances to true
+            // so that we don't delete children in Studio that aren't tracked.
+            if context.has_git_filter() {
+                snapshot.metadata.ignore_unknown_instances = true;
+                // Also apply this recursively to all children
+                set_ignore_unknown_instances_recursive(&mut snapshot.children);
+            }
         }
         output
     }
@@ -365,6 +391,16 @@ impl Middleware {
     }
 }
 
+/// Recursively sets `ignore_unknown_instances` to `true` on all children.
+/// This is used when git filter is active to ensure we don't delete
+/// children in Studio that aren't tracked by Rojo.
+fn set_ignore_unknown_instances_recursive(children: &mut [InstanceSnapshot]) {
+    for child in children {
+        child.metadata.ignore_unknown_instances = true;
+        set_ignore_unknown_instances_recursive(&mut child.children);
+    }
+}
+
 /// A helper for easily defining a SyncRule. Arguments are passed literally
 /// to this macro in the order `include`, `middleware`, `suffix`,
 /// and `exclude`. Both `suffix` and `exclude` are optional.

src/snapshot_middleware/project.rs

@@ -192,6 +192,17 @@ pub fn snapshot_project_node(
         }
 
         (_, None, _, Some(PathNode::Required(path))) => {
+            // If git filter is active and the path was filtered out, treat it
+            // as if the path was optional and skip this node.
+            if context.has_git_filter() {
+                log::trace!(
+                    "Skipping project node '{}' because its path was filtered by git filter: {}",
+                    instance_name,
+                    path.display()
+                );
+                return Ok(None);
+            }
+
             anyhow::bail!(
                 "Rojo project referred to a file using $path that could not be turned into a Roblox Instance by Rojo.\n\
                 Check that the file exists and is a file type known by Rojo.\n\
@@ -282,7 +293,12 @@ pub fn snapshot_project_node(
     // If the user didn't specify it AND $path was not specified (meaning
     // there's no existing value we'd be stepping on from a project file or meta
     // file), set it to true.
-    if let Some(ignore) = node.ignore_unknown_instances {
+    //
+    // When git filter is active, always set to true to preserve descendants
+    // in Studio that are not tracked by Rojo.
+    if context.has_git_filter() {
+        metadata.ignore_unknown_instances = true;
+    } else if let Some(ignore) = node.ignore_unknown_instances {
         metadata.ignore_unknown_instances = ignore;
     } else if node.path.is_none() {
         // TODO: Introduce a strict mode where $ignoreUnknownInstances is never

src/syncback/ref_properties.rs

@@ -8,7 +8,10 @@ use rbx_dom_weak::{
     ustr, Instance, Ustr, WeakDom,
 };
 
-use crate::{multimap::MultiMap, REF_ID_ATTRIBUTE_NAME, REF_POINTER_ATTRIBUTE_PREFIX};
+use crate::{
+    multimap::MultiMap, syncback::snapshot::inst_path, REF_ID_ATTRIBUTE_NAME,
+    REF_POINTER_ATTRIBUTE_PREFIX,
+};
 
 pub struct RefLinks {
     /// A map of referents to each of their Ref properties.
@@ -50,6 +53,22 @@ pub fn collect_referents(dom: &WeakDom) -> RefLinks {
                 continue;
             }
 
+            let target = match dom.get_by_ref(*prop_value) {
+                Some(inst) => inst,
+                None => {
+                    // Properties that are Some but point to nothing may as
+                    // well be `nil`. Roblox and us never produce these values
+                    // but syncback prunes trees without adjusting ref
+                    // properties for performance reasons.
+                    log::warn!(
+                        "Property {}.{} will be `nil` on the disk because the actual value is not being included in syncback",
+                        inst_path(dom, inst_ref),
+                        prop_name
+                    );
+                    continue;
+                }
+            };
+
             links.insert(
                 inst_ref,
                 RefLink {
@@ -58,10 +77,6 @@ pub fn collect_referents(dom: &WeakDom) -> RefLinks {
                 },
             );
 
-            let target = dom
-                .get_by_ref(*prop_value)
-                .expect("Refs in DOM should point to valid Instances");
-
             // 1. Check if target has an ID
             if let Some(id) = get_existing_id(target) {
                 // If it does, we need to check whether that ID is a duplicate

tests/tests/syncback.rs

@@ -71,8 +71,13 @@ syncback_tests! {
     ref_properties_conflict => ["src/Pointer_2.model.json", "src/Target_2.model.json"],
     // Ensures that having multiple pointers that are aimed at the same target doesn't trigger ref rewrites.
     ref_properties_duplicate => [],
+    // Ensures that ref properties that point to nothing after the prune both
+    // do not leave any trace of themselves
+    ref_properties_pruned => ["src/Pointer1.model.json", "src/Pointer2.model.json", "src/Pointer3.model.json"],
     // Ensures that the old middleware is respected during syncback
     respect_old_middleware => ["default.project.json", "src/model_json.model.json", "src/rbxm.rbxm", "src/rbxmx.rbxmx"],
+    // Ensures that the `$schema` field roundtrips with syncback
+    schema_roundtrip => ["default.project.json", "src/model.model.json", "src/init/init.meta.json", "src/adjacent.meta.json"],
     // Ensures that StringValues inside project files are written to the
     // project file, but only if they don't have `$path` set
     string_value_project => ["default.project.json"],
@@ -81,5 +86,4 @@ syncback_tests! {
     sync_rules => ["src/module.modulescript", "src/text.text"],
     // Ensures that the `syncUnscriptable` setting works
     unscriptable_properties => ["default.project.json"],
-    schema_roundtrip => ["default.project.json", "src/model.model.json", "src/init/init.meta.json", "src/adjacent.meta.json"]
 }