Bazel, Buck2, potentially other similar environments

Starlark-based build systems with the ability to compile a code generator and invoke it as a genrule will run CXX's C++ code generator via its cxxbridge command line interface.

The tool is packaged as the cxxbridge-cmd crate on crates.io or can be built from the gen/cmd/ directory of the CXX GitHub repo.

$  cargo install cxxbridge-cmd

$  cxxbridge src/bridge.rs --header > path/to/bridge.rs.h
$  cxxbridge src/bridge.rs > path/to/bridge.rs.cc

Important: The version number of cxxbridge-cmd used for the C++ side of the binding must always be identical to the version number of cxx used for the Rust side. You must use some form of lockfile or version pinning to ensure that this is the case.

The CXX repo maintains working Bazel BUILD.bazel and Buck2 BUCK targets for the complete blobstore tutorial (chapter 3) for your reference, tested in CI. These aren't meant to be directly what you use in your codebase, but serve as an illustration of one possible working pattern.

# tools/bazel/rust_cxx_bridge.bzl

load("@bazel_skylib//rules:run_binary.bzl", "run_binary")
load("@rules_cc//cc:defs.bzl", "cc_library")

def rust_cxx_bridge(name, src, deps = []):
    native.alias(
        name = "%s/header" % name,
        actual = src + ".h",
    )

    native.alias(
        name = "%s/source" % name,
        actual = src + ".cc",
    )

    run_binary(
        name = "%s/generated" % name,
        srcs = [src],
        outs = [
            src + ".h",
            src + ".cc",
        ],
        args = [
            "$(location %s)" % src,
            "-o",
            "$(location %s.h)" % src,
            "-o",
            "$(location %s.cc)" % src,
        ],
        tool = "//:codegen",
    )

    cc_library(
        name = name,
        srcs = [src + ".cc"],
        deps = deps + [":%s/include" % name],
    )

    cc_library(
        name = "%s/include" % name,
        hdrs = [src + ".h"],
    )

# demo/BUILD.bazel

load("@rules_cc//cc:defs.bzl", "cc_library")
load("@rules_rust//rust:defs.bzl", "rust_binary")
load("//tools/bazel:rust_cxx_bridge.bzl", "rust_cxx_bridge")

rust_binary(
    name = "demo",
    srcs = glob(["src/**/*.rs"]),
    deps = [
        ":blobstore-sys",
        ":bridge",
        "//:cxx",
    ],
)

rust_cxx_bridge(
    name = "bridge",
    src = "src/main.rs",
    deps = [":blobstore-include"],
)

cc_library(
    name = "blobstore-sys",
    srcs = ["src/blobstore.cc"],
    deps = [
        ":blobstore-include",
        ":bridge/include",
    ],
)

cc_library(
    name = "blobstore-include",
    hdrs = ["include/blobstore.h"],
    deps = ["//:core"],
)