TODO(b/274102056): Write summary on this docs when close to completion.
The bindings generators components of Crubit are being released, and it's released by the Crosstool release process.
Specifically, bindings generators components that are in Crosstool release are:
The bindings generator tools:
They are built from the targets above and released at google3/nowhere/llvm/rust/crubit/bin/.
Crubit support libraries: support/.
They are copied as source files and transformed and are released at google3/nowhere/llvm/rust/crubit/support/.
This means that when you bazel build, say a rust_binary with cc_deps:
The “released” version of the cc_bindings_from_rs bindings generator tool in third_party/crosstool is invoked to generate the Rust binding, instead of the one freshly-built from with the latest and your workspace changes.
The “released” version of the Crubit support libraries are used in your bindings.
The following sections are meant for Crubit developers.
Concretely, a “Crubit flavor” is a combination of build flag values that impacts which Crubit is used and how Crubit is built.
2 boolean flags determine flavor of Crubit:
//google_internal/build_flavors:on_demand: if true, use Crubit built from your workspace which has your local changes, otherwise, use the prebuilt binding generators in one of the Crosstool directories. --config=crubit-on-demand for short.
//third_party/crosstool:unstable_flag: if true, use Crosstool unstable toolchains in all build actions - notably, the actions that build Crubit binding generators (if on-demand), the actions that build Rust crates (e.g., for a rust_binary with cc_deps) or C++ libraries, otherwise use the Crosstool stable toolchains. --config=llvm-unstable for short.
The combination of the 2 boolean flags results in the 4 following Crubit flavors. (google_internal/build_flavors/crubit_build_flavor_defs.bzl has the full specification and exports crubit_build_flavors for easier reference.)
stable : Uses the prebuilt Crubit in Crosstool stable directory, which gets released by rapid/llvm_crosstool ~weekly.
This is also the `default` flavor of Crubit.
llvm_unstable : Uses the prebuilt Crubit in Crosstool unstable directory. rapid/rust_crosstool_unstable builds Crosstool unstable Crubit bindings generators using the freshly bootstrapped “unstable” rust toolchain ~daily.
This flavor is useful for exercising the process of rebuilding Crubit binding generators and branching the support library source file, before the Crosstool stable release. For example, it can catch the case that the dependency of Crubit support libraries isn't visible from Crosstool directories.
on_demand_built_with_llvm_unstable : Uses the Crubit built from your workspace that has your local changes using the Crosstool unstable toolchains (rustc, rustc-as-a-library, clang, etc.) throughout.
This will soon be the default flavor for Crubit *development*. This flavor is useful for detecting upstream rustc changes that are incompatible with Crubit, before Crosstool release: Crubit depends closely on rustc-as-a-library API, which isn't stable; upstream rustc library changes are first surfaced through Crosstool unstable rust.
on_demand_built_with_llvm_stable : Similar to on_demand_built_with_llvm_unstable, except that Crosstool stable toolchains (rustc, rustc-as-a-library, clang, etc.) is used throughout the build.
This flavor combination exists, but it won't be exercised by TAP/Guitar. It may become helpful as a backup for local development in case Crosstool unstable toolchains are broken.