Buck2 rules for building WebAssembly components.
⚠️ Experimental: The structure and APIs are going to change to better support usage as a Buck2 external cell. Currently, this is a collection of experiments and patterns for WASM component development with Buck2.
cargo +nightly-2025-06-20 install --git https://github.com/facebook/buck2.git buck2
# Run the example validator
buck2 run //runner:validator -- "Hello World"
buck2 run //runner:validator -- "Hello#World"- Component Building: Create WASM components from Rust, C, and C++
- WIT Bindings: Generate language bindings from WIT definitions
- Composition: Link and plug components together
- Package Management: Fetch components from WASM registries
load("@toolchains//wasm:component.bzl", "wasm_component")
# Build the C++ binary with WASM target using wasi-sdk
rust_binary(
name = "regex",
crate = "regex",
crate_root = "src/lib.rs",
edition = "2024",
srcs = glob(["src/**/*.rs"]) + glob(["wit/**/*.wit"]),
deps = [
"//third-party:regex",
"//third-party:wit-bindgen",
],
)
# Promote output of regex to wasm component
wasm_component(
name = "regex_component",
module = ":regex",
wit = "wit/regex.wit",
visibility = ['PUBLIC'],
)wasm_component- Create component from WASM modulewasm_component_link- Link multiple componentswasm_plug- Compose components using wacwasm_validate- Validate WASM binarieswasm_print- Convert WASM to text format
wit_bindgen_rust- Generate Rust bindingswit_bindgen_c- Generate C bindingswit_bindgen_cxx- Generate C++ bindingswit_to_markdown- Generate documentation
wasm_package- Download packages from registries
# Regex component (Rust)
rust_binary(
name = "regex_lib",
srcs = glob(["src/**/*.rs"]),
)
wasm_component(
name = "regex_component",
module = ":regex_lib",
wit = "wit/regex.wit",
)
# Validator component (C++)
wit_bindgen_cxx(
name = "validator_bindings",
world = "validator",
wit = ["wit/validator.wit"],
)
cxx_binary(
name = "validator",
srcs = ["src/validator.cpp"],
deps = [":validator_bindings"],
)
wasm_component(
name = "validator_component",
module = ":validator",
wit = "wit/validator.wit",
)
# Compose: plug regex into validator
wasm_plug(
name = "app",
socket = ":validator_component",
plugs = [":regex_component"],
)All toolchains are hermetic - they download specific versions of tools rather than relying on system installations. This ensures reproducible builds across different environments.
Each toolchain is composed of two parts:
- Distribution: Downloads and extracts the tool binary
- Toolchain: Provides convenient wrappers and subcommands
This separation makes it easy to control tool sources and versions:
# Download the distribution
download_wasm_tools(
name = "wasm_tools_dist",
version = "1.239.0",
)
# Create toolchain from distribution
wasm_tools_toolchain(
name = "wasm_tools",
distribution = ":wasm_tools_dist",
visibility = ["PUBLIC"],
)Available toolchains:
- wasm-tools - Component manipulation (https://github.com/bytecodealliance/wasm-tools)
- wit-bindgen - Binding generation (https://github.com/bytecodealliance/wit-bindgen)
- wac - Component composition (https://github.com/bytecodealliance/wac)
- wkg - Package management (https://github.com/bytecodealliance/wasm-pkg-tools)
- wasi-sdk - C/C++ wasi toolchain (https://github.com/WebAssembly/wasi-sdk)