c7d78534d2
This finishes the work started in
https://github.com/emscripten-core/emsdk/pull/1388 by fixing CI. It
avoids a breaking change by:
* Using the latest rules_js 1.x.x version, instead of updating to
rules_js 2 (which removes support for bazel 5).
* Copying the contents of
[rules_js_dependencies](https://github.com/aspect-build/rules_js/blob/main/js/repositories.bzl)
instead of calling it, as the call would need to be added by users in
their `WORKSPACE` files
Context from the previous PR:
> Bazel's Node.js dependency comes from
[rules_nodejs](https://github.com/bazelbuild/rules_nodejs/). Previously,
bazel/deps.bzl was using rules_nodejs 5.8.0, released in 2022 and only
supported Node.js toolchains up to 18.12.1.
> This PR bumps rules_nodejs to latest 6.1.1. It also replaces
build_bazel_rules_nodejs with
[rules_js](https://github.com/aspect-build/rules_js), since npm_install
that bazel/emscripten_deps.bzl used was deprecated. The README of
rules_nodejs now recommends migrating to rules_js for everything other
than the Node.js toolchain:
(371e8cab15)
> Impetus
Our repo builds with Bazel and uses Emscripten and Node.js. Tried to
upgrade Node.js 18 to Node.js 20 and saw that emsdk didn't support
rules_nodejs 6+ in the same workspace.
Similarly, it's not possible to update to rules_js v2 in a workspace
that also references `emsdk`.
Bazel Emscripten toolchain
Setup Instructions
In WORKSPACE file, put:
load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
git_repository(
name = "emsdk",
remote = "https://github.com/emscripten-core/emsdk.git",
tag = "3.1.64",
strip_prefix = "bazel",
)
load("@emsdk//:deps.bzl", emsdk_deps = "deps")
emsdk_deps()
load("@emsdk//:emscripten_deps.bzl", emsdk_emscripten_deps = "emscripten_deps")
emsdk_emscripten_deps(emscripten_version = "3.1.64")
load("@emsdk//:toolchains.bzl", "register_emscripten_toolchains")
register_emscripten_toolchains()
The tag and emscripten_version parameters correspond to the git revision of
emsdk 3.1.64. To get access to
newer versions, you'll need to update those. To make use of older versions, change the
parameter of git_repository and emsdk_emscripten_deps(). Supported versions are listed in revisions.bzl
Bazel 7+ additionally requires platforms dependencies in the MODULE.bazel file.
bazel_dep(name = "platforms", version = "0.0.9")
Building
Put the following line into your .bazelrc:
build --incompatible_enable_cc_toolchain_resolution
Then write a new rule wrapping your cc_binary.
load("@rules_cc//cc:defs.bzl", "cc_binary")
load("@emsdk//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.
wasm_cc_binary uses transition to use emscripten toolchain on cc_target
and all of its dependencies, and does not require amending .bazelrc. This
is the preferred way, since it also unpacks the resulting tarball.
The Emscripten cache shipped by default does not include LTO, 64-bit or PIC
builds of the system libraries and ports. If you wish to use these features you
will need to declare the cache when you register the toolchain as follows. Note
that the configuration consists of the same flags that can be passed to
embuilder. If targets is not provided, all system libraries and ports will be
built, i.e., the ALL option to embuilder.
load("@emsdk//:toolchains.bzl", "register_emscripten_toolchains")
register_emscripten_toolchains(cache = {
"configuration": ["--lto"],
"targets": [
"crtbegin",
"libprintf_long_double-debug",
"libstubs-debug",
"libnoexit",
"libc-debug",
"libdlmalloc",
"libcompiler_rt",
"libc++-noexcept",
"libc++abi-debug-noexcept",
"libsockets"
]
})
See test_external/ for an example using embind.