Using Cargo2gn

Overview

Rust uses Cargo as its build system and package manager. Cargo.toml is the manifest file of Cargo. It contains metadata such as the name, version, and dependencies for crates (packages) in Rust.

When used in OpenHarmony, Cargo.toml needs to be converted into BUILD.gn rules. cargo2gn is the tool that can achieve this purpose. It can convert one or more Rust libraries.

Converting a Single Library

Go to the directory of the rust library to be converted, for example, bindgen.
```
cd openharmony/third_party/rust/bindgen
```

Create the configuration file cargo2gn.json.

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

Run the following command to perform the conversion:

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

The conversion result is as follows:

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"]
}

Converting Multiple Libraries in Batches

Go to the rust directory.
```
cd openharmony/third_party/rust
```
Add all the rust libraries to be converted to [workspace] in Cargo.toml in the rust directory.
```
[workspace]
members = [
    "aho-corasick",
    "memchr",
]
```
Perform steps 2 and 3 in section "Converting a Single Library".