| # Reproducible builds |
| |
| Crubit can emit bindings for Rust or C++ libraries so that they can be called |
| from the other language, but these bindings require strict ABI compatibility. To |
| accomplish this, Crubit uses `clang` and `rustc` as libraries to discover the |
| public APIs of the wrapped libraries, and the ABI that they expose when built |
| (e.g. their function calling conventions, and the memory layout of their |
| structs). |
| |
| To ensure that the generated bindings are ABI-compatible with the built |
| libraries, Crubit needs to see exactly what the real compiler sees: |
| |
| * Build the wrapped libraries using the same version of the compiler that |
| Crubit uses, with the same compilation settings (flags, environment |
| variables, etc.). For example, an extra `-DSOME_DEFINE` or a new version of |
| the compiler can completely change the ABI, or even the API, of a given |
| library. If the compiler sees it, but Crubit does not, the generated |
| bindings will be incorrect. |
| * Do not store Crubit outputs (*e.g.* `..._cc_api.h` or `..._rs_api.rs`) in a |
| source code repository, as they *will* go out of date. Crubit comes with |
| Bazel integration support to invoke it at build time. |
| * The ABI must be deterministic and reproducible (*i.e.* depend only on |
| compilation settings, the compiler version, and the wrapped libraries |
| themselves). For example, the |
| [`-Zrandomize-layout`](https://github.com/rust-lang/compiler-team/issues/457) |
| flag cannot be used without a fixed seed. |
