rules_rust

Rustc is very tightly coupled with cargo. Nothing stops you from calling rustc yourself, but you basically need to reverse engineer what cargo is doing. My reference for this is https://github.com/bazelbuild/rules_rust which needs to pass a bunch of CARGO_ envvars to get stuff to build, among various other required conventions.

The same reason Bazel builds avoid using Cargo when building Rust software, so I'll describe why Bazel would do this: - Bazel wants to cache remote resources, like each respective crate's source files. - Bazel then wants to build each crate in a sandbox, and cache the build artifacts. Because bazel owns this process, instead of Cargo, it can trivially distribute those build artifacts to other developers, or in CI, etc -- instead of everyone having to build everything from scratch. This is an established practice, and Nix wants to drive the build for the same reasons. See: - https://github.com/bazelbuild/rules_rust - https://github.com/google/cargo-raze