Cargo2gn工具操作指导

概述

rust三方库使用cargo编译，配置为Cargo.toml。集成到OpenHarmony上需要转换成BUILD.gn规则。为了满足这个需求，需要提供一个cargo2gn转换工具。当需要引入rust三方crate时使用cargo2gn转换工具来把三方库的Cargo.toml转换成BUILD.gn规则。cargo2gn可以单个库进行转换，也可以多个库进行批量转换。

单个库转换操作步骤

进入到需要转化的rust三方库的目录下，比如需要转化bindgen。
```
cd openharmony/third_party/rust/bindgen
```

创建配置文件cargo2gn.json，可以参考如下配置。

{
    "copy-out": true,
    "run": true,
    "add-workspace": true,
    "cargo-bin": "/mnt/xxx/openharmony/prebuilts/rustc/linux-x86_64/current/bin"
}

执行以下命令进行转换。

python3 /mnt/xxx/openharmony/build/scripts/cargo2gn.py --config cargo2gn.json

转换结果

import("//build/templates/rust/ohos_cargo_crate.gni")

ohos_cargo_crate("lib") {
    crate_name = "bindgen"
    crate_type = "rlib"
    crate_root = "./lib.rs"

    sources = ["./lib.rs"]
    edition = "2018"
    cargo_pkg_version = "0.64.0"
    cargo_pkg_authors = "Jyun-Yan You <jyyou.tw@gmail.com>,  Emilio Cobos Álvarez <emilio@crisal.io>,  Nick Fitzgerald <fitzgen@gmail.com>,  The Servo project developers"
    cargo_pkg_name = "bindgen"
    cargo_pkg_description = "Automatically generates Rust FFI bindings to C and C++ libraries."
    deps = [
        "//third_party/rust/bitflags:lib",
        "//third_party/rust/cexpr:lib",
        "//third_party/rust/clang-sys:lib",
        "//third_party/rust/lazy_static:lib",
        "//third_party/rust/lazycell:lib",
        "//third_party/rust/log:lib",
        "//third_party/rust/peeking_take_while:lib",
        "//third_party/rust/proc-macro2:lib",
        "//third_party/rust/quote:lib",
        "//third_party/rust/regex:lib",
        "//third_party/rust/rustc-hash:lib",
        "//third_party/rust/shlex:lib",
        "//third_party/rust/syn:lib",
        "//third_party/rust/which:lib",
    ]
    features = [
        "default",
        "log",
        "logging",
        "static",
        "which",
        "which-rustfmt",
    ]
    build_root = "build.rs"
    build_sources = ["build.rs"]
    build_script_outputs = ["host-target.txt"]
}

多个库批量转换操作步骤

进入到rust目录下。
```
cd openharmony/third_party/rust
```
把所有需要转换的rust三方库添加到rust目录下的Cargo.toml的[workspace]里，如下所示。
```
[workspace]
members = [
    "aho-corasick",
    "memchr",
]
```
执行单个库转换操作步骤的2和3。