Bazel Emscripten toolchain

Setup Instructions

1. Merge the WORKSPACE file in with your own at the root of your bazel directory structure. If you don't have one, simply copy the file.
2. Merge the bazelrc file in with your .bazelrc file at the root of your bazel directory structure. If you don't have one, simply copy the file and rename it to .bazelrc. (Note the .)
3. Copy the emscripten_toolchain folder along with its contents to the root of your bazel directory.

Your directory structure should look like this:

bazel_root/
├── .bazelrc
├── WORKSPACE
├── emscripten_toolchain/
│   ├── BUILD.bazel
│   ├── builddefs.bzl
│   ├── crosstool.bzl
│   ├── emar.sh
│   ├── emcc.sh
│   ├── emcc_link.sh
│   ├── emscripten.BUILD
│   ├── emscripten_config
│   ├── env.sh
│   ├── link_wrapper.py
│   ├── wasm_binary.py
│   ├── wasm_cc_binary.bzl
│   ├── wasm_rules.bzl
├── your_project_folder/
│   ├── your_project.file

Building

Using --config=wasm

Simply pass --config=wasm when building a normal cc_binary. The result of this build will be a tar archive containing any files produced by emscripten.

Using wasm_cc_binary

First, write a new rule wrapping your cc_binary.

load("@rules_cc//cc:defs.bzl", "cc_binary")
load("//emscripten_toolchain:wasm_rules.bzl", "wasm_cc_binary")

cc_binary(
    name = "hello-world",
    srcs = ["hello-world.cc"],
)

wasm_cc_binary(
    name = "hello-world-wasm",
    cc_target = ":hello-world",
)

Now you can run bazel build :hello-world-wasm. The result of this build will be the individual files produced by emscripten. Note that some of these files may be empty. This is because bazel has no concept of optional outputs for rules.