Crubit Features

NOTE: b/262878759: Features are currently only used for autogenerated Rust bindings of C++ targets, not C++ bindings of Rust targets. Even without specifying any features, Crubit will generate full C++ bindings for Rust targets. This will change soon.

C++/Rust interop is configured per target using “features”: aspect hints which are applied onto a build target in order to configure its automatically generated bindings.

Features control which capabilities Crubit has. For example, support for move constructors is gated behind the :experimental feature. If the class is in a target configured to use :experimental, then the constructor will receive bindings, otherwise it will not.

Features are used for gradual rollouts of new capabilities, and to allow for separate build modes for un-annotated code, code which opts into C++/Rust interop, and internal test code.

To use a feature, add it to your target:

# Enables the `:supported` feature on a C++ library `:example`.
cc_library(
    name = "example",
    hdrs = ["example.h"],
    aspect_hints = ["//features:supported"],
)

This causes the generated bindings for that target to use all the Crubit capabilities in :supported.

Features

The default feature is enabled for all targets everywhere. It contains interop capabilities which have minimal impositions on library owners.

The default feature currently only enables a “dark launch” parsing and processing pass. No bindings are generated.

"//features:supported"

The supported feature enables generally-available C++/Rust interop capabilities, for libraries that specifically support FFI callers.

See for documentation on what this includes.

"//features:extern_c" {#extern_c}

extern_c is the feature for the in-development version of Crubit. For calling C++ from Rust, use :supported instead.

"//features:experimental"

The experimental feature enables internal-only experimental capabilities. This is used for testing of upcoming features, and is also used by pilot partners who are testing those features. This also includes everything in :supported.

experimental is visibility-restricted to only internal use and pilot partners.