rs: add rules_rust_bindgen extension

[bazaah]

Note

This PR depends on the changes in hermeticbuild/rules_rust#31

This is basically a shim around the underlying extension in hermeticbuild/rules_rust, and notably we do not provide a default toolchain for bindgen -- users are expected to provide their own.

This can be easily done if using hermeticbuild/hermetic-llvm, as it provides targets for clang, libclang and libstdcxx.

---

I provide the toolchain myself via a crate extension for bindgen-cli and then @llvm for the llvm bits:

load("@rules_rust_bindgen//:defs.bzl", "rust_bindgen_toolchain")

package(default_visibility = ["//visibility:public"])

toolchain(
    name           = "toolchain",
    toolchain      = "bindgen_toolchain_impl",
    toolchain_type = "@rules_rust_bindgen//:toolchain_type",
)

rust_bindgen_toolchain(
    name      = "bindgen_toolchain_impl",
    bindgen   = ":bindgen",
    clang     = "@llvm-project//clang:clang",
    libclang  = "@llvm-project//clang:libclang",
    libstdcxx = ":libstdcxx",
)

alias(
    name = "bindgen",
    actual = "@bindgen_toolchain_tools//:bindgen-cli__bindgen",
)

cc_import(
    name            = "libstdcxx",
    hdrs            = ["@llvm//runtimes/libstdcxx:headers_include_search_directory"],
    shared_library  = "@llvm//runtimes/libstdcxx:libstdcxx.shared",
    visibility      = ["//visibility:public"],
)

@bindgen_toolchain_tools//:bindgen-cli__bindgen

# bindgen.MODULE.bazel
package = "<label of parent package where this MODULE.bazel is>"

bindgen_toolchain_tools = use_extension("@rules_rs//rs:extensions.bzl", "crate")

bindgen_toolchain_tools.annotation(
    crate = "bindgen-cli",
    gen_binaries = ["bindgen"],
)

bindgen_toolchain_tools.from_cargo(
    name = "bindgen_toolchain_tools",
    cargo_lock = package + ":Cargo.lock",
    cargo_toml = package + ":Cargo.toml",
    platform_triples = ["..."],
)

use_repo(
    bindgen_toolchain_tools,
    "bindgen_toolchain_tools",
)

# Cargo.toml
[package]
name    = "bindgen-tool"
version = "1.0.0"
edition = "2021"

[lib]
crate-type = ["lib"]
path = "empty.rs" # needed to satisfy @rules_rs

[dependencies.bindgen]
version  = "0.72"
features = [
  "runtime",
]

[dependencies.bindgen-cli]
version  = "0.72"
features = [
  "runtime",
]

[dependencies.clang-sys]
git = "https://github.com/KyleMayes/clang-sys"
rev = "a76fd89f1800155e06f99ec5e200a02aadb49e3f"
features = [
  "clang_20_0",
  "runtime",
]

[patch.crates-io]
clang-sys = { git = "https://github.com/KyleMayes/clang-sys", rev = "a76fd89f1800155e06f99ec5e200a02aadb49e3f" }

See https://bazelbuild.slack.com/archives/C05UNC5AANQ/p1782926171232299?thread_ts=1782822956.695739&cid=C05UNC5AANQ for the context of where this is coming from.