从 CI 下载预构建的工具链（clang、rust）
usage: fx download-toolchain <toolchain>[:<target>] [...]
Downloads one or more prebuilt toolchains (`clang` or `rust`)
for the current host architecture (${HOST_PLATFORM}) into
`//local/<toolchain>` and prints the GN arguments needed to use them.
Arguments:
<toolchain> One of `clang` or `rust`.
Downloads the latest green build from toolchain.ci
for the current host architecture.
<toolchain>:<target> Download `<toolchain>` from a specific build or
builder. `<target>` can be:
- A LUCI / Milo build URL (e.g.
https://ci.chromium.org/ui/p/fuchsia/builders/.../b8666755190352362065/overview
or https://ci.chromium.org/b/8666755190352362065)
- A Buildbucket build ID (e.g. b8666755190352362065
or 8666755190352362065)
- A CAS digest (e.g. <sha256>/<size_bytes>)
- A LUCI builder URL or builder name (e.g.
fuchsia/toolchain.ci/rust_llvm-linux-x64 or
rust_llvm-linux-x64), which resolves to the
latest green build on that builder.
Examples:
fx download-toolchain rust
fx download-toolchain clang rust
fx download-toolchain \
clang:https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci/clang-linux-x64/b8666747240201415809/overview \
rust:https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci/rust_llvm-linux-x64/b8666927100188196401/overview