typespec_rs 0.4.2

# typespec-rs

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[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](LICENSE)
[![crates.io](https://img.shields.io/crates/v/typespec_rs.svg)](https://crates.io/crates/typespec_rs)
[![tspc](https://img.shields.io/crates/v/tspc.svg)](https://crates.io/crates/tspc)

A Rust implementation of the [TypeSpec](https://typespec.io/) type system — parser, type checker, and emitter.

## What is TypeSpec?

[TypeSpec](https://typespec.io/) is a language for describing cloud service APIs. It lets you define models, operations, and services declaratively, then generate OpenAPI, JSON Schema, protobuf, and other formats from a single source of truth.

**typespec-rs** is an independent Rust port of the TypeSpec compiler — not a binding to the TypeScript compiler. It implements the parser, checker, and emitter pipeline natively in Rust.

> **Note:** This project is not affiliated with or endorsed by Microsoft. TypeSpec is a trademark of Microsoft Corporation.

## Status

This project is in **early development**. The core compiler pipeline works:

| Component | Status |
|-----------|--------|
| Scanner/Lexer | Complete |
| Parser | Complete |
| Type Checker | Working |
| YAML Emitter | Working |
| JSON Emitter | Working |
| OpenAPI 3 Emitter | Working |
| Protobuf Library | Working |
| CLI (`tspc`) | Working |
| WASM Extensions | Working |
| Programmatic Decorator API | Working |

2,840+ tests passing.

## Quick Start

### Library

Add to your `Cargo.toml`:

```toml
[dependencies]
typespec_rs = "0.4.0"
```

Parse TypeSpec and emit YAML/JSON:

```rust
use typespec_rs::emit::{to_yaml, to_json};

let src = r#"
    model Pet {
        id: string;
        name: string;
        age?: int32;
        type: "dog" | "cat" | "bird";
    }
"#;

let yaml = to_yaml(src).unwrap();
println!("{}", yaml.output);

let json = to_json(src).unwrap();
println!("{}", json.output);
```

### CLI

Install `tspc`:

```bash
cargo install tspc
```

Or download pre-built binaries from [GitHub Releases](https://github.com/ejfkdev/typespec-rs/releases).

Usage:

```bash
# Parse to JSON (default)
tspc petstore.tsp

# Parse to YAML
tspc -f yaml petstore.tsp

# Generate OpenAPI 3.0
tspc -f openapi petstore.tsp

# OpenAPI 3.1
tspc -f openapi --openapi-version 3.1.0 petstore.tsp

# Write to file
tspc -f openapi petstore.tsp -o petstore.openapi.json

# Type-check only
tspc --no-emit petstore.tsp

# Read from stdin
echo 'model Pet { name: string }' | tspc -f json -
```

## Custom Decorators

typespec-rs provides two ways to register custom decorators:

### Programmatic Registration (Recommended)

Register decorators directly on the `Checker` before calling `check_program()`. This bypasses source parsing, so it works with reserved keywords (`flag`, `arg`, `env`) and complex types without type resolution issues:

```rust
use typespec_rs::checker::Checker;
use typespec_rs::parser;

let parse_result = parser::parse(source);
let mut checker = Checker::new();
checker.set_parse_result(parse_result.root_id, parse_result.builder.clone());

// Register custom decorators
checker.register_decorator("command", "CLI", "Operation");
checker.register_decorator("flag", "CLI", "unknown");
checker.register_decorator("env", "CLI", "unknown");

// Or batch registration
checker.register_decorators(vec![
    ("route", "HTTP", "Operation"),
    ("tag", "API", "unknown"),
]);

checker.check_program();
```

If the namespace doesn't exist yet, it will be created automatically under the global namespace. Duplicate registrations (same name + namespace) are silently skipped.

### Library Source Injection

For decorators that need parameter type information, inject TypeSpec source via the library registry:

```rust
use typespec_rs::parser::{parse, register_library};
use typespec_rs::libs::http::http_library_source;

// Register at startup
register_library("http", http_library_source());

// parse() now automatically injects all registered libraries
let result = parse(source);
```

### ParseOptions Presets

For one-off usage without global state:

```rust
use typespec_rs::parser::{Parser, ParseOptions};

// With HTTP library
let result = Parser::new(source, ParseOptions::with_http()).parse();

// With HTTP + custom libraries
let result = Parser::new(source, ParseOptions::with_http_and(vec![
    custom_lib_source,
])).parse();

// Builder pattern
let result = Parser::new(source, ParseOptions::new(vec![])
    .library(http_library_source())
    .library(custom_lib),
).parse();
```

## WASM Extensions (Experimental)

`tspc` supports loading WASM extensions for custom decorators and output formats. Enable the `wasm-extensions` feature:

```toml
[dependencies]
tspc = { version = "0.4.0", features = ["wasm-extensions"] }
```

```bash
# Load a WASM extension
tspc -f markdown -e my_extension.wasm petstore.tsp
```

WASM extensions can:
- Declare custom decorators (registered programmatically, avoiding keyword conflicts)
- Handle decorator invocation during type checking
- Read/write decorator state via `tsp.state_set` / `tsp.state_get` host functions
- Report diagnostics back to the compiler
- Provide custom emitters for new output formats

### WASM Extension ABI

A WASM extension must export the following functions:

| Export | Signature | Description |
|--------|-----------|-------------|
| `allocate` | `(i32) -> i32` | Allocate `n` bytes in guest memory |
| `deallocate` | `(i32, i32)` | Free guest memory |
| `tsp_ext_manifest` | `() -> i32` | Return pointer to JSON manifest |
| `tsp_ext_manifest_len` | `() -> i32` | Return manifest length |
| `tsp_ext_init` | `(i32, i32) -> i32` | Initialize with options JSON |
| `tsp_ext_handle_decorator` | `(i32, i32) -> i32` | Handle a decorator application |
| `tsp_ext_emit` | `(i32, i32) -> i32` | Emit output from type graph JSON |
| `tsp_ext_emit_len` | `() -> i32` | Return emit output length |

And can import host functions from the `tsp` namespace:

| Import | Signature | Description |
|--------|-----------|-------------|
| `tsp.log` | `(ptr, len)` | Log a message |
| `tsp.state_set` | `(key_ptr, key_len, type_id, val_ptr, val_len)` | Set decorator state |
| `tsp.state_get` | `(key_ptr, key_len, type_id) -> i32` | Get state (returns length or -1) |
| `tsp.state_get_read` | `(buf_ptr)` | Copy last state_get result to guest |
| `tsp.state_add` | `(key_ptr, key_len, type_id)` | Add to state set |
| `tsp.state_has` | `(key_ptr, key_len, type_id) -> i32` | Check state (1/0) |
| `tsp.report_diagnostic` | `(severity, code_ptr, code_len, msg_ptr, msg_len)` | Report diagnostic |

### Manifest Format

The manifest JSON returned by `tsp_ext_manifest`:

```json
{
  "name": "my-extension",
  "version": "1.0.0",
  "formats": ["markdown", "custom"],
  "decorators": [
    {
      "name": "myDecorator",
      "namespace": "MyExt",
      "target_types": ["Model"],
      "parameters": [{ "name": "value", "type": "string" }]
    }
  ]
}
```

### Execution Flow

1. **Pre-parse**: Extension manifests are extracted; decorators registered on the Checker
2. **Parse + Check**: User source is parsed and type-checked (decorators resolved from registry)
3. **Decorator handling**: For each type with a matching decorator, `tsp_ext_handle_decorator` is called with `{ "type_id": N, "decorator_name": "...", "args": [...] }`
4. **Emit**: If the extension handles the requested format, `tsp_ext_emit` is called with the serialized type graph JSON

## Examples

Run with `cargo run --example <name>`:

| Example | Description |
|---------|-------------|
| `quick_start` | Convert TypeSpec to YAML/JSON in 5 lines |
| `model_examples` | Model definitions with optional fields, unions, arrays |
| `parse_and_inspect` | Low-level AST parsing and inspection |
| `petstore` | Full PetStore API parsing example |
| `tsp_to_json` | Parse and emit with JSON/YAML output |

## Architecture

```
Source Code → Scanner → Parser → AST → Checker → Typed AST → Emitter → Output
```

- **Scanner** (`scanner/`) — Tokenizes TypeSpec source into `TokenKind` stream
- **Parser** (`parser/`) — Builds an AST from the token stream
- **Checker** (`checker/`) — Type checking, symbol resolution, decorator validation
- **Emitter** (`emit/`) — Converts checked types to YAML, JSON, or OpenAPI
- **CLI** (`crates/tspc/`) — Command-line interface with WASM extension support
- **Libs** (`libs/`) — Built-in library sources (HTTP, OpenAPI, etc.)

## Feature Coverage

What's ported from the [TypeSpec compiler](https://github.com/microsoft/typespec):

- Full scanner with doc comments, string templates, conflict markers
- Complete parser for all declaration types
- Type system with 25+ type kinds (Model, Interface, Enum, Union, Scalar, Template, etc.)
- Type relation/assignability checking
- Decorator application and validation
- Template declaration and instantiation
- Standard library types (string, int32, float64, utcDateTime, etc.)
- Helper libraries: HTTP types, status codes, content types, URI templates, OpenAPI/OpenAPI3/JSON Schema/protobuf/versioning type definitions
- External library injection API for custom decorator declarations
- Programmatic decorator registration (`Checker::register_decorator`) — bypasses source parsing, supports reserved keywords
- WASM extension system with wasmtime runtime — custom decorators and emitters
- CLI with cross-platform binary releases (UPX compressed)
- `fn` function declarations with `extern` modifier and call validation
- `internal` access control with project/library visibility scoping
- HTTP response handling: union variant flattening, plain body detection, response indexing
- Linter rule options with JSON Schema validation and default value merging
- OpenAPI emitter with HTTP-protocol-aware verb/route/parameter resolution
- Protobuf proto3 `optional` label logic with array/map warnings
- ICE-protected diagnostic creation (fallback instead of panic)
- Templated alias member expression resolution with default parameter instantiation

What's not yet ported:

- Full `Program` pipeline (multi-file compilation, import resolution)
- Decorator execution at `finishType` time
- Language Server Protocol (LSP) support
- Source loader (async I/O)

## Development

```bash
# Run tests
cargo test --lib

# Run CLI tests
cargo test -p tspc

# Run linter
cargo clippy --all-targets

# Check formatting
cargo fmt --all -- --check

# Build docs
cargo doc --no-deps

# Run examples
cargo run --example quick_start
```

## Dependencies

| Crate | Purpose |
|-------|---------|
| [`regex`](https://crates.io/crates/regex) | Pattern matching in scanner |
| [`bitflags`](https://crates.io/crates/bitflags) | Bitflag types for visibility, symbol flags |

## Contributing

Contributions are welcome! Please see [CONTRIBUTING.md](CONTRIBUTING.md) for guidelines.

## License

This project is licensed under the [MIT License](LICENSE).

## Security

See [SECURITY.md](SECURITY.md) for vulnerability reporting guidelines.