C++ nullability analysis

Annotating C++ API boundaries with nullability information can improve their Rust bindings (e.g. binding non-null pointers as T& rather than Option<T&>).

This directory has tools for C++ codebases that use such annotations:

• Nullability inference suggests annotations to add to APIs, by analyzing the code that implements and uses them.

• Nullability verification verifies that annotated APIs are used and implemented safely, e.g. checking nullable pointers before dereferencing them. This is a local analysis suitable for use in a clang-tidy check.

They use Clang, its dataflow framework, and its nullability annotations.

Style

This directory mostly uses LLVM-style C++, rather than Google-style C++ used in the rest of crubit/. The goal is to make it easy to upstream into clang-tidy once mature.

Specifically:

• We follow the LLVM coding standards, with the exceptions listed here.
• We use absl CHECK() rather than assert(). (This finds bugs more reliably, and is trivial to migrate later.)
• We otherwise avoid relying on absl, using llvm's Support libraries instead.
• We write // TODO instead of // FIXME.

This list isn‘t set in stone: we can choose to diverge further from LLVM style, if it’s worth more cost of upstreaming later.