Rust Wasm Bindgen


Bazel rules for generating wasm modules for Javascript using wasm-bindgen.


To begin using the wasm-bindgen rules, users can load the necessary dependencies in their workspace by adding the following to their WORKSPACE.bazel file.

load("@rules_rust//wasm_bindgen:repositories.bzl", "rust_wasm_bindgen_dependencies", "rust_wasm_bindgen_register_toolchains")



This should enable users to start using the rust_wasm_bindgen rule. However, it’s common to want to control the version of wasm-bindgen in the workspace instead of relying on the one provided by rules_rust. In this case, users should avoid calling rust_wasm_bindgen_register_toolchains and instead use the rust_wasm_bindgen_toolchain rule to define their own toolchains to register in the workspace.

Interfacing with Javascript rules

While it’s recommended for users to mantain their own , in the @rules_rust//wasm_bindgen package there exists interface sub-packages for various Javascript Bazel rules. E.g. build_bazel_rules_nodejs or aspect_rules_js. The rules defined there are a more convenient way to use rust_wasm_bindgen with the associated javascript rules due to the inclusion of additional providers. Each directory contains a defs.bzl file that defines the different variants of rust_wasm_bindgen. (e.g. nodejs_rust_wasm_bindgen for the rules_nodejs submodule).


rust_wasm_bindgen(name, bindgen_flags, target, wasm_file)

Generates javascript and typescript bindings for a webassembly module using wasm-bindgen.

An example of this rule in use can be seen at @rules_rust//examples/wasm


Name Description Type Mandatory Default
name A unique name for this target. Name required  
bindgen_flags Flags to pass directly to the bindgen executable. See for details. List of strings optional []
target The type of output to generate. See for details. String optional "bundler"
wasm_file The .wasm file or crate to generate bindings for. Label required  


rust_wasm_bindgen_toolchain(name, bindgen)

The tools required for the rust_wasm_bindgen rule.

In cases where users want to control or change the version of wasm-bindgen used by rust_wasm_bindgen, a unique toolchain can be created as in the example below:

load("@rules_rust//bindgen:bindgen.bzl", "rust_bindgen_toolchain")

    bindgen = "//3rdparty/crates:wasm_bindgen_cli__bin",

    name = "wasm_bindgen_toolchain",
    toolchain = "wasm_bindgen_toolchain_impl",
    toolchain_type = "@rules_rust//wasm_bindgen:toolchain_type",

Now that you have your own toolchain, you need to register it by inserting the following statement in your WORKSPACE file:


For additional information, see the Bazel toolchains documentation.


Name Description Type Mandatory Default
name A unique name for this target. Name required  
bindgen The label of a wasm-bindgen-cli executable. Label optional None


RustWasmBindgenInfo(js, ts, wasm)

Info about wasm-bindgen outputs.


Name Description
js Depset[File]: The Javascript files produced by wasm-bindgen.
ts Depset[File]: The Typescript files produced by wasm-bindgen.
wasm File: The .wasm file generated by wasm-bindgen.



Declare dependencies needed for the rules_rust wasm-bindgen rules.


list[struct(repo=str, is_dev_dep=bool)]: A list of the repositories defined by this macro.



Registers the default toolchains for the rules_rust wasm-bindgen rules.


Name Description Default Value
register_toolchains Whether or not to register toolchains. True