3391e039d6
This script is (IMO) more readable, but the real reason for this change is that it raises an error message when the binary package fails to download. (The shell script silently generated a bogus hash instead, because the shell's `set -e` builtin does not affect commands executing inside a $() context. It seemed just as easy to rewrite the script in Python as to fix that. This change also updates some outdated filename references.
Bazel Emscripten toolchain
Setup Instructions
In WORKSPACE file, put:
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
http_archive(
name = "emsdk",
sha256 = "d55e3c73fc4f8d1fecb7aabe548de86bdb55080fe6b12ce593d63b8bade54567",
strip_prefix = "emsdk-3891e7b04bf8cbb3bc62758e9c575ae096a9a518/bazel",
url = "https://github.com/emscripten-core/emsdk/archive/3891e7b04bf8cbb3bc62758e9c575ae096a9a518.tar.gz",
)
load("@emsdk//:deps.bzl", emsdk_deps = "deps")
emsdk_deps()
load("@emsdk//:emscripten_deps.bzl", emsdk_emscripten_deps = "emscripten_deps")
emsdk_emscripten_deps(emscripten_version = "2.0.31")
load("@emsdk//:toolchains.bzl", "register_emscripten_toolchains")
register_emscripten_toolchains()
The SHA1 hash in the above strip_prefix and url parameters correspond to the git revision of
emsdk 2.0.31. To get access to
newer versions, you'll need to update those. To make use of older versions, change the
parameter of emsdk_emscripten_deps(). Supported versions are listed in revisions.bzl
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.
See test_external/ for an example using embind.