Why doesn't rules_rust respect the mod keyword?

[davidmcnamee]

I have a small dummy project here where I've been playing around with rules_rust:

.
├── BUILD.bazel
├── Cargo.lock
├── Cargo.toml
├── WORKSPACE
└── src
    ├── BUILD.bazel
    ├── app
    │   ├── BUILD.bazel
    │   ├── app.rs
    │   └── mod.rs
    └── main.rs

// src/main.rs
mod app;
use app::app::app;
// ...

// src/app/mod.rs
pub mod app;

// src/app/app.rs
pub fn app(cx: Scope) -> Element { /* ... */ }

But rules_rust doesn't seem to build unless I remove the mod app; line in src/main.rs and change use app::app::app; -> use app::app;. See here for build error.

The result is that cargo run never works at the same time as bazel run, because their linking system is different. Am I doing something wrong, or is this intended?

[davidmcnamee]

I think I understand now... rust_library and rust_binary deps attributes will statically link the binaries together, which means it is accessible using the optional extern crate keyword as described here as opposed to the mod keyword. (Correct me if I'm wrong here)

The rust module system seems incompatible with bazel's efficient compilation and linking of binaries, since you'd have to tell bazel about all the files in your project upfront. So I'm going to close this.

It did help to find the crate_name attribute on rust_library, which will at least make my imports more closely match the file structure. Hope this helps anyone else who happens upon this post.