Rest - Deep Dive

Rest is a Rust binary that uses the OXC toolchain to compile TypeScript 2-3x faster than esbuild while producing output compatible with VSCode’s build process.

Architecture 🏗️

Compilation pipeline: source files pass through OXC parser, transformer, and code generator in sequence. Optional parallel mode processes multiple files concurrently.

Modules

Path
`Source/Library.rs` - Binary entry point, CLI parsing, compiler dispatch
`Source/Fn/OXC/Compiler.rs` - Main orchestration: parser, transformer, codegen
`Source/Fn/OXC/Parser.rs` - Wraps `oxc_parser` with error normalization
`Source/Fn/OXC/Transformer.rs` - TypeScript-to-JavaScript AST transformations
`Source/Fn/OXC/Codegen.rs` - JavaScript generation from transformed AST
`Source/Fn/Build.rs` - Directory-based compilation preserving structure
`Source/Fn/Bundle/` - Bundling utilities
`Source/Fn/NLS/` - Natural Language Support string extraction
`Source/Fn/SWC/` - SWC integration shims (alternative transformer path)
`Source/Fn/Worker/` - Worker thread support for parallel compilation
`Source/Struct/CompilerConfig.rs` - Configuration: decorators, class fields, source maps

Compilation Flow 🔄

CLI / RestPlugin -> Compiler
  -> Parser (OXC Parser) -> AST + diagnostics
  -> Transformer -> Transformed AST
  -> Codegen -> JavaScript text
  -> Write .js file to output directory

Transformer applies:

emitDecoratorMetadata (VSCode compatibility)
useDefineForClassFields=false (matches VSCode gulp build)
TypeScript type stripping

When --Parallel is specified, file compilation fans out across Tokio worker threads.

VSCode Compatibility Settings ⚙️

Option	Value	Description
Decorator metadata	`true`	Required for VSCode dependency injection
Class fields mode	`false`	Matches VSCode’s gulp build behavior
Source maps	development only	Inline maps for debug builds

Configuration ⚙️

CLI Flag	Default	Description
`--Input`	required	Directory or file to compile
`--Output`	required	Destination for compiled JavaScript
`--Parallel`	off	Multi-core parallel compilation

Integration 🔗

Element	Direction	Mechanism
Output	Consumer	Process invocation / esbuild plugin
Cocoon	Indirect	Loads JS from `Target/Microsoft/VSCode/`
Sky	Indirect	Loads VSCode UI components via Output package