rules_wasm_component

Production-ready Bazel rules for building WebAssembly components across multiple languages with native WASI 0.2 support.

• Multi-language: Build components from Rust, Go (TinyGo), C++, JavaScript/TypeScript
• Production Ready: OCI publishing, cryptographic signing, WAC composition, AOT compilation
• Bazel Native: Hermetic builds, aggressive caching, cross-platform (Windows/macOS/Linux)
• Zero Shell Scripts: Pure Bazel implementation for maximum portability

Add to your MODULE.bazel:

bazel_dep(name = "rules_wasm_component", version = "1.0.0")

load("@rules_wasm_component//rust:defs.bzl", "rust_wasm_component")
rust_wasm_component(
 name = "my_service",
 srcs = ["src/lib.rs"],
 wit = ":service_wit",
 profiles = ["debug", "release"],
)

load("@rules_wasm_component//go:defs.bzl", "go_wasm_component")
go_wasm_component(
 name = "calculator",
 srcs = ["main.go"],
 wit = ":calculator_wit",
 world = "calculator",
)

load("@rules_wasm_component//cpp:defs.bzl", "cpp_component")
cpp_component(
 name = "calculator",
 srcs = ["calculator.cpp"],
 wit = ":calculator_wit",
 cxx_std = "c++20",
)

load("@rules_wasm_component//wac:defs.bzl", "wac_compose")
wac_compose(
 name = "full_system",
 components = {
 ":frontend": "app:frontend",
 ":backend": "app:backend",
 },
 composition = '''
 let frontend = new app:frontend { ... };
 let backend = new app:backend { ... };
 connect frontend.request -> backend.handler;
 export frontend as main;
 ''',
)

• Rust (1.90.0+): Multi-profile builds, Clippy integration, Wizer pre-initialization
• Go (TinyGo 0.39.0): Native WASI 0.2, hermetic Go module resolution
• C++ (WASI SDK 27): C++17/20/23, cross-package headers, LTO optimization
• JavaScript/TypeScript (jco 1.4.0, Node.js 20.18.0): NPM dependencies, componentize-js

• WAC Composition: Official WebAssembly Composition standard for multi-component systems
• OCI Publishing: Push components to Docker/OCI registries
• Cryptographic Signing: wasmsign2 integration for supply chain security
• AOT Compilation: Wasmtime precompilation for 87% size reduction and faster startup
• Wizer Pre-initialization: 1.35-6x startup improvement for Rust components
• Multi-Profile Builds: Debug, release, and custom optimization profiles

• Hermetic Toolchains: All tools downloaded automatically, no system dependencies
• Cross-Platform: Native Windows/macOS/Linux support without WSL
• Comprehensive Examples: 20+ working examples from basic to advanced patterns

See MODULE.bazel for current versions — the single source of truth.

All toolchains are hermetically downloaded and version-pinned for reproducible builds.

Complete Rule Reference — All rules, attributes, and providers

Guides:

• Toolchain Configuration
• Multi-Profile Builds
• Development Guidelines

Examples:

• Basic Component
• Multi-Language Composition
• Wizer Pre-initialization
• OCI Publishing
• See all examples

• WIT-enabled Go components currently fail due to upstream TinyGo limitations
• Tracking: Issue #82
• Basic Go components (without WIT) work perfectly

• WASI disables C++ exceptions by default for size/performance
• Use enable_exceptions = True for components that require exceptions (Issue #83)

Contributions welcome! See CONTRIBUTING.md for details.

Apache-2.0 — see LICENSE.