Why does Rust require a C++ toolchain to produce a Rust binary, while languages like Go do not have this requirement?

Question

Compiling a Rust file with rustc foo.rs fails if I don't have a C++ toolchain installed. But when compiling a Go program, such a toolchain is not required. Why is that?

Answer 1

TL;DR: Because everyone has a C toolchain.

Slight correction: rustc does not require a C++ toolchain, it only requires a C toolchain. Notably, rustc created binaries only depend on libc (or equivalent), not on libstdc++ (or equivalent).

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As Go demonstrated, it is possible to not require a C toolchain. You only need to re-implement its functionality:

• You need to implement your own linker, respecting the target platform format.
• You need to implement your own libc (aka OS layer).

There are advantages to doing so, such as possibly faster compilation or easier cross-compiling, however there is a cost in doing the implementation, and it's easy to get things wrong.

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The Rust community preferred to put more effort into the language than in the toolchain, and therefore reusing the stock toolchain was easier. Specifically, rustc will require a platform linker (ld on Unix) and platform equivalent to libc.

This is not a core design principle, it's just a pragmatic approach, and there are projects to cut down on these dependencies:

• Using lld rather than ld would allow shipping a single linker with rustc which can target all platforms.
• Using cranelift as an alternative backend could also remove the dependency on ld.
• The Redox project is working on relibc, a portable Rust implementation of the libc API.

Those are all work in progress, and in the meantime rustc will require a C toolchain. Furthermore, even in the foreseeable future, I would expect rustc to require a C toolchain for targets not yet covered by any Rust toolchain, just so you can use the target without waiting for some hypothetical development.