rojo/.cursor/rules/src.mdc

---
description: "Rust server/CLI implementation: snapshot system, middleware, commands, syncback, and web API architecture."
globs:
  - "src/**/*.rs"
  - "crates/**/*.rs"
---

# Rojo Server/CLI (Rust)

Core implementation: CLI, HTTP/WebSocket server, snapshot system, filesystem transformations.

**Entry:** `src/main.rs` (CLI) | `src/lib.rs` (public API)

## Core Systems

### 1. Snapshot System (`src/snapshot/`)

Pure functions: filesystem → instance tree → minimal patches → apply changes

**Key files:**
- `mod.rs` - System overview with detailed explanation
- `patch_compute.rs` - Generate diffs
- `patch_apply.rs` - Apply changes
- `instance_snapshot.rs` - Core snapshot type

```rust
pub struct InstanceSnapshot {
    pub snapshot_id: Ref,
    pub metadata: InstanceMetadata,
    pub name: Cow<'static, str>,
    pub class_name: Ustr,
    pub properties: UstrMap<Variant>,
    pub children: Vec<InstanceSnapshot>,  // Nested snapshots, not Refs!
}
```

### 2. Snapshot Middleware (`src/snapshot_middleware/`)

Transforms files → `InstanceSnapshot`. Main entry: `snapshot_from_vfs()`

| File | Handler | Result | Note |
|------|---------|--------|------|
| `*.luau` | `lua.rs` | ModuleScript | Preferred |
| `*.server.luau` | `lua.rs` | Script (RunContext.Server) | Preferred |
| `*.client.luau` | `lua.rs` | Script (RunContext.Client) | Preferred |
| `*.plugin.luau` | `lua.rs` | Script (RunContext.Plugin) | |
| `*.local.luau` | `lua.rs` | LocalScript | |
| `*.legacy.luau` | `lua.rs` | Script (RunContext.Legacy) | |
| `*.lua` | `lua.rs` | ModuleScript | Legacy |
| `*.server.lua` | `lua.rs` | Script (RunContext.Legacy) | Legacy |
| `*.client.lua` | `lua.rs` | LocalScript | Legacy |
| `*.rbxm` / `*.rbxmx` | `rbxm.rs` / `rbxmx.rs` | Binary/XML model tree | |
| `*.model.json5` | `json_model.rs` | JSON instance | Preferred |
| `*.model.json` | `json_model.rs` | JSON instance | Legacy |
| `*.project.json5` | `project.rs` | Nested project | Preferred |
| `*.project.json` | `project.rs` | Nested project | Legacy |
| `*.csv` / `*.txt` | `csv.rs` / `txt.rs` | LocalizationTable / StringValue | |
| `*.toml` / `*.json5` / `*.yaml` | Data → ModuleScript | |
| Directory | `dir.rs` | Folder or inferred service | |
| `*.meta.json5` | `meta_file.rs` | Metadata overlay | Preferred |
| `*.meta.json` | `meta_file.rs` | Metadata overlay | Legacy |

**Init files:** `init.luau`, `init.server.luau`, etc. → Instance named after parent directory (`.lua` legacy supported)

**Context passed to middleware:**

```rust
pub struct InstanceContext {
    pub path_ignore_rules: Arc<Vec<PathIgnoreRule>>,
    pub sync_rules: Vec<SyncRule>,
}
```

**Filename handling (syncback/two-way sync):**

Instance names with forbidden filesystem chars (`<>:"/\|?*`) are handled by:
1. `slugify_name()` -- replaces forbidden chars with `_` (pure, stateless)
2. `deduplicate_name()` -- appends `~1`, `~2`, etc. on collision (stateful)
3. Metadata `name` field -- stores the real instance name in `.meta.json5`/`.model.json5` when the slug differs

### 3. Commands (`src/cli/`)

- `serve.rs` - Live sync with WebSocket
- `build.rs` - Generate rbxl/rbxm/rbxmx/rbxlx
- `upload.rs` - Upload to Roblox.com
- `sourcemap.rs` - Generate sourcemaps
- `syncback.rs` - Roblox → filesystem
- `init.rs` / `fmt_project.rs` / `doc.rs` / `plugin.rs`

### 4. Syncback (`src/syncback/`)

Reverse: Roblox file → filesystem

- `snapshot.rs` - Convert instances to snapshots
- `fs_snapshot.rs` - Filesystem representation
- `hash/` - Content hashing for change detection
- `property_filter.rs` - Apply syncback rules

### 5. Web Server (`src/web/`)

- `api.rs` - HTTP/WebSocket endpoints
- `interface.rs` - Browser UI
- Protocol version enforcement

### 6. Project System (`src/project.rs`)

Parse/validate `.project.json5` (or legacy `.project.json`), handle nested projects, manage sync rules.

## Command Implementations

### `rojo serve`

1. Load project
2. Build initial snapshot tree
3. Start HTTP server (Hyper)
4. Open WebSocket at `/api/rojo`
5. Watch filesystem (memofs VFS)
6. Generate patches on changes
7. Send to connected plugins

**Key:** `src/serve_session.rs` manages active sessions

### `rojo build`

1. Load project
2. Build snapshot tree
3. Convert to `WeakDom` (rbx_dom_weak)
4. Serialize with `rbx_binary` or `rbx_xml`
5. Write output

**Flags:** `--output`, `--plugin`, `--watch`

### `rojo syncback`

1. Load project
2. Read Roblox file (rbxl/rbxm)
3. Parse with `rbx_binary`
4. Match instances to project
5. Write files per syncback rules

**Rules:**
```rust
pub struct SyncbackRules {
    ignore_trees: Vec<String>,           // Roblox tree paths to ignore
    ignore_paths: Vec<String>,           // Filesystem path patterns
    ignore_properties: IndexMap<Ustr, Vec<Ustr>>,  // Class → properties
    ignore_classes: Vec<String>,         // Classes to skip entirely
    sync_current_camera: Option<bool>,   // Default: false
    sync_unscriptable: Option<bool>,     // Default: true
    ignore_referents: Option<bool>,      // Skip Ref properties, default: false
}
```

## Error Handling Patterns

**CLI (anyhow):**
```rust
use anyhow::{Context, Result};

pub fn load_project(path: &Path) -> Result<Project> {
    fs::read_to_string(path)
        .context("Failed to read project file")?;
    // ...
}
```

**Library (thiserror):**
```rust
use thiserror::Error;

#[derive(Debug, Error)]
pub enum SnapshotError {
    #[error("Instance {0} not found")]
    InstanceNotFound(Ref),
}
```

**Context chaining:**
```rust
.with_context(|| format!("Failed for {}", path.display()))?
```

## Testing

**Unit tests:** Co-located with code
```rust
#[cfg(test)]
mod tests {
    use super::*;
    
    #[test]
    fn test_something() {
        assert_eq!(result, expected);
    }
}
```

**Integration tests:** `tests/` directory with `gen_build_tests!` macro

**Snapshot tests:** `insta` crate
```rust
use insta::assert_snapshot;

#[test]
fn test_output() {
    let result = build_something();
    assert_snapshot!(result);
}
```

Review: `cargo insta review`

**Test utilities:** `tests/rojo_test/` - io_util, roundtrip_util, serve_util, syncback_util

## Web API

**HTTP:**
- `GET /` - Browser UI
- `GET /api/rojo` - Server info (version, project name, protocol)

**WebSocket:** `ws://host:port/api/rojo`

**Protocol v5:**
```json
// Handshake
{"type": "ServerInfo", "protocolVersion": 5, "serverVersion": "7.7.0"}

// Patch
{
  "type": "ApplyPatch",
  "sessionId": "<uuid>",
  "patch": {
    "removed": [id1, id2],
    "added": {id3: {...}},
    "updated": {id4: {changedProperties: {...}}}
  }
}
```

**Session:** `src/serve_session.rs` manages state, VFS, message queue

## Project File Structure

**ProjectNode:**
```rust
pub struct ProjectNode {
    pub class_name: Option<Ustr>,                       // $className
    pub id: Option<String>,                             // $id for Ref linking
    pub children: BTreeMap<String, ProjectNode>,        // Child nodes (flattened)
    pub properties: BTreeMap<Ustr, UnresolvedValue>,    // $properties
    pub attributes: BTreeMap<String, UnresolvedValue>,  // $attributes
    pub ignore_unknown_instances: Option<bool>,         // $ignoreUnknownInstances
    pub path: Option<PathNode>,                         // $path
}
```

**SyncRule:**
```rust
pub struct SyncRule {
    pub include: Glob,           // Serialized as "pattern"
    pub exclude: Option<Glob>,   // Optional exclusion pattern
    pub middleware: Middleware,  // Serialized as "use"
    pub suffix: Option<String>,  // Optional suffix to trim
    pub base_path: PathBuf,      // Internal: glob base path
}
```

## Common Operations

**Load project:**
```rust
use librojo::Project;
let project = Project::load_from_slice(path, contents)?;
```

**Build snapshot:**
```rust
use librojo::{InstanceContext, snapshot_from_vfs};
let snapshot = snapshot_from_vfs(&context, &vfs, &path)?;
```

**Generate patch:**
```rust
use librojo::snapshot::compute_patch_set;
let patch = compute_patch_set(&old_snap, &new_snap, &old_tree, &new_tree);
```

**Serialize to binary:**
```rust
use rbx_binary::to_writer;
use rbx_dom_weak::WeakDom;

let dom = WeakDom::new(root);
to_writer(&mut buffer, &dom, dom.root())?;
```

## Performance

**Profiling:** Enable Tracy with `--features profile-with-tracy`

**Optimization:** Use `#[profiling::function]` on hot paths

**Parallelization:** Use `rayon` for parallel operations (sparingly - I/O often bottlenecks)

**VFS:** `memofs::Vfs` caches file contents, invalidates on watch events

## Key Dependencies

**Core:** rbx_binary, rbx_xml, rbx_dom_weak, memofs (local crate)
**Async:** tokio, hyper, hyper-tungstenite
**Serialization:** serde, json5, toml, yaml-rust2, csv
**Utilities:** clap, anyhow, thiserror, crossbeam-channel, rayon, globset

## Module Organization

See `src/snapshot/mod.rs` for canonical example:
- Module doc explaining purpose, data flow
- Private submodules, public exports
- Tests in `#[cfg(test)] mod tests`

## Contributing Guidelines

### Adding File Type Support

1. Create middleware in `src/snapshot_middleware/`
2. Add to `Middleware` enum
3. Register in `snapshot_from_vfs()`
4. Add syncback support if applicable
5. Add tests in `rojo-test/build-tests/`

### Adding Command

1. Create file in `src/cli/`
2. Add to `Subcommand` enum
3. Implement with clap derives
4. Add `run()` method

### Modifying Snapshots

**Critical:** Add extensive tests first, consider migration path, test with real projects

## Debugging

**Verbose logging:**
```bash
RUST_LOG=trace rojo serve
RUST_LOG=rojo=debug rojo build
```

**Inspect snapshots:** Add `eprintln!("Snapshot: {:#?}", snapshot);`

**Test specific middleware:** Create minimal test in `rojo-test/build-tests/`

**Watch events:** `RUST_LOG=memofs=trace`

**Protocol issues:** Browser dev tools on `http://localhost:34872`

## Common Pitfalls

**Path separators:** Always use `Path::join()`, never string concatenation
**Watch events:** Can fire multiple times - use `change_processor` to dedupe
**Property types:** Use rbx_reflection to validate expected types
**Protocol version:** Bump in both plugin AND server when changing communication
**Backwards compat:** Support legacy formats where possible

## File Locations

```
src/
  cli/           - Commands
  snapshot/      - Core system
  snapshot_middleware/ - File handlers
  syncback/      - Reverse sync
  web/           - HTTP/WebSocket
  lib.rs         - Public API
  main.rs        - CLI entry

crates/
  memofs/        - Virtual filesystem

tests/
  rojo_test/     - Test utilities
  tests/         - Integration tests
```

## Additional Resources

- **Snapshot system:** `src/snapshot/mod.rs` (comprehensive explanation)
- **Middleware examples:** `src/snapshot_middleware/lua.rs`, `dir.rs`
- **Test examples:** `tests/tests/build.rs`, `serve.rs`
- **Project parsing:** `src/project.rs`