tool-support.md

Rust/C++ Interop Tool Support

This document is an initial, partially reviewed draft

This table describes how various Rust/C++ interop use cases and problems are supported by major interop tooling, including the Rust compiler:

• Crubit auto-generates a wide range of supported Rust and C++ interop bindings. Glue code and customisation is in the original source code, and the build system. Currently depends on the bazel build system, but they are actively working on cargo integration.
• cxx: auto-generates supported safe Rust and C++ interop bindings. Glue code is in the original source code, customisation and recent language features are limited. Compatible with multiple build systems, including cargo.
• Zngur: auto-generates a wide range of declared Rust and C++ interop bindings, focusing on accessing Rust from C++. Glue code is in C++, as the more expressive language. Declarations and customisation are in .zng IDL files. Compatible with multiple build systems.

Key:
⛔ No Support
🔁 In progress
◓ Basic or Partial Support
✅ Good Support
? Needs Analysis
blank Out of Scope

Use Case or Problem Statement	rustc	Crubit	cxx	Zngur
Async C++/Rust Interop		✅	◓	✅
Basic Types	rustc	Crubit	cxx	Zngur
Compatible type layouts	◓	✅	✅	✅
Create a vector containing FFI types		✅	⛔	✅
Call C++ Iterators from Rust		✅	✅	✅
Use FFI string types		✅	✅	✅
Match standard library type layouts	◓	◓	◓
Lossless FFI integer type mappings	◓	✅1
Convert Rust & C++ Result types		✅	✅
Unify C++ forward decls to Rust types		◓	◓
Advanced Types	rustc	Crubit	cxx	Zngur
Init C++ objects in-place in Rust	🔁2	✅	⛔	✅
Passing non-POD types	◓	✅	✅	✅
Use a prefix of the full Rust/C++ type	🔁3	✅	✅	?
Rust Traits for C++ Types	◓	✅	◓?	✅
Rust dyn traits from C++	?	◓	⛔	✅
Cross-language class inheritance		◓	⛔	✅
C++ templates with Rust types		✅	⛔	✅
Define a C++ enum from Rust	◓4	✅	✅
Safety	rustc	Crubit	cxx	Zngur
Cross-language object ownership		✅	◓	✅
Lifetimes in C++ code		✅	◓
FFI thread safety	◓	◓	?	?
Rust & C++ unwinding compatibility	◓	⛔	✅	✅
Skip non-null pointer null checks	?	✅	⛔	◓
Allocator FFI compatibility	🔁5	✅	✅	✅
Overloading	rustc	Crubit	cxx	Zngur
Call an overloaded C++ function from Rust	🔁6	◓	◓	◓
Type-dependent C++ call safety	🔁7	?	⛔
Building & Linking	rustc	Crubit	cxx	Zngur
Add Rust to existing C/C++ builds	◓8	◓	✅	✅
Link Time Optimisation (LTO) Interop	◓	✅	✅	✅

Footnotes

1. ffi_11 crate ↩

2. Rust project goal ↩

3. Rust compiler experiment, requires a Rust UnsafeCell to wrap C++ mutable class members ↩

4. Rust nightly lang experiment ↩

5. Rust Zulip discussions ↩

6. Rust compiler experiment ↩

7. Rust RFC ↩

8. Rust stabilisation RFC ↩