Rest provides the technical foundation TypeScript compiler within the Land project. Rest is a Rust binary that uses the OXC toolchain to compile TypeScript 2-3x faster than esbuild while producing output compatible with VS Code’s build process.

Architecture

Rest is structured as a Rust library with a binary entry point. The compilation pipeline passes source files through OXC’s parser, transformer, and code generator in sequence. An optional parallel mode processes multiple files concurrently across CPU cores.

graph TB
    subgraph "Rest - TypeScript Compiler"
        Binary["Library.rs - Binary Entry Point"]
        CLI["CLI Argument Parsing\n--Input · --Output · --Parallel"]
        Compiler["Fn/OXC/Compiler.rs\nOrchestration"]
        Parser["Fn/OXC/Parser.rs\nOXC Parser"]
        Transformer["Fn/OXC/Transformer.rs\nAST Transformation"]
        Codegen["Fn/OXC/Codegen.rs\nCode Generation"]
        Config["Struct/CompilerConfig.rs\nConfiguration"]
    end

    subgraph "OXC Toolchain"
        OXCParser["oxc_parser\nTypeScript / JSX"]
        OXCTransform["oxc_transformer\nDecorators · Class Fields"]
        OXCCodegen["oxc_codegen\nJS Output"]
        OXCSemantic["oxc_semantic\nSymbol Table"]
    end

    subgraph "Output Integration"
        RestPlugin["Output/RestPlugin.ts\nesbuild plugin"]
        TargetRest["Target/Rest/\nCompiled artifacts"]
        TargetFinal["Target/Microsoft/VSCode/\nMerged final output"]
    end

    Binary --> CLI
    CLI --> Compiler
    Compiler --> Parser
    Parser --> OXCParser
    Compiler --> Transformer
    Transformer --> OXCTransform
    Transformer --> OXCSemantic
    Compiler --> Codegen
    Codegen --> OXCCodegen
    Compiler --> Config
    Codegen --> TargetRest
    RestPlugin --> Compiler
    TargetRest --> TargetFinal

Key Modules

Path	Description
`Source/Library.rs`	Binary entry point; parses CLI arguments and dispatches to compiler
`Source/Fn/OXC/Compiler.rs`	Main compilation orchestrator; coordinates parser, transformer, and codegen
`Source/Fn/OXC/Parser.rs`	Wraps `oxc_parser` with error normalization and source tracking
`Source/Fn/OXC/Transformer.rs`	Applies TypeScript-to-JavaScript AST transformations including decorators
`Source/Fn/OXC/Codegen.rs`	Generates final JavaScript text from the transformed AST
`Source/Fn/Build.rs`	Directory-based compilation: walks source trees preserving structure
`Source/Fn/Bundle/`	Bundling utilities for multi-file outputs
`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 struct: decorator mode, class fields, source maps
`Source/Struct/SWC.rs`	SWC-specific configuration types

Data Flow

sequenceDiagram
    participant CLI as CLI / RestPlugin
    participant Compiler as Compiler Orchestrator
    participant Parser as OXC Parser
    participant Transformer as OXC Transformer
    participant Codegen as OXC Codegen
    participant Disk as Output Directory

    CLI->>Compiler: Compile(input_path, config)
    Compiler->>Parser: Parse(source_text)
    Parser->>Compiler: AST + diagnostics
    Compiler->>Transformer: Transform(AST, options)
    Note over Transformer: emitDecoratorMetadata\nuseDefineForClassFields=false\nTypeScript stripping
    Transformer->>Compiler: Transformed AST
    Compiler->>Codegen: Generate(AST)
    Codegen->>Compiler: JavaScript text
    Compiler->>Disk: Write .js file
    Compiler->>CLI: CompilationResult (count, elapsed, errors)

When --Parallel is specified, the compiler fans out file compilation across Tokio worker threads and collects aggregated metrics.

Integration Points

Connecting Element	Direction	Mechanism	Description
Output	Consumer	Process invocation / esbuild plugin	Output’s `RestPlugin.ts` invokes the Rest binary or calls it via plugin API
Cocoon	Indirect consumer	Compiled artifacts	Cocoon loads the JavaScript produced by Rest from `Target/Microsoft/VSCode/`
Sky	Indirect consumer	`@codeeditorland/output` package	Sky loads VS Code UI components compiled through the Rest pipeline

Configuration

Option	CLI Flag / Variable	Default	Description
Input path	`--Input`	required	Directory or file to compile
Output path	`--Output`	required	Destination directory for compiled JavaScript
Parallel mode	`--Parallel`	off	Enable multi-core parallel compilation
Decorator metadata	`CompilerConfig`	`true`	Emit `emitDecoratorMetadata` for VS Code compatibility
Class fields mode	`CompilerConfig`	`false` (VS Code default)	`useDefineForClassFields` - off matches VS Code’s gulp build
Source maps	`CompilerConfig`	development only	Inline source maps for debug builds

The CompilerConfig struct is populated from either CLI flags or from the esbuild plugin context when Rest is invoked as a plugin within the Output build pipeline.