substrate-wasm-builder

WASM builder is an utility for building a project as a WASM binary

The WASM builder is a tool that integrates the building of a WASM binary of your project into the main cargo build process.

Project setup

A project that should be compiled as WASM binary needs to add a build.rs, add substrate-wasm-builder-runner as dependency into build-dependencies and requires to have a feature called no-std. The build.rs needs to contain the following code:

use wasm_builder_runner::{build_current_project, WasmBuilderSource};

fn main() {
	build_current_project(
		// The name of the file being generated in out-dir.
		"wasm_binary.rs",
		// How to include wasm-builder, in this case from crates.io.
		WasmBuilderSource::Crates("1.0.0"),
	);
}

The no-std feature will be enabled by WASM builder while compiling your project to WASM.

As a last step you need to add the following to your project:

include!(concat!(env!("OUT_DIR"), "/wasm_binary.rs"));

This will include the generated wasm binary as two constants WASM_BINARY and WASM_BINARY_BLOATY. The former is the WASM binary compacted and the later without compaction.

Environment variables

By using environment variables, you can configure which WASM binaries are build and how:

• SKIP_WASM_BUILD - Skips building any WASM binary. This is useful when only native should be recompiled.
• BUILD_DUMMY_WASM_BINARY - Builds dummy WASM binaries. These dummy binaries are empty and useful for cargo check runs.
• WASM_BUILD_TYPE - Sets the build type for building WASM binaries. Supported values are release or debug. By default the build type is equal to the build type used by the main build.

Each project can be skipped individually by using the environment variable SKIP_PROJECT_NAME_WASM_BUILD. Where PROJECT_NAME needs to be replaced by the name of the cargo project, e.g. node-runtime will be NODE_RUNTIME.

Prerequisites:

WASM builder requires the following prerequisities for building the WASM binary:

• rust nightly + wasm32-unknown-unknown toolchain
• wasm-gc