How to include file from another file in the same directory of the same project?

Question

I started a new project in rust (it's my first project in rust, but my first programming language). I added a few functions, types and unit test in main.rs. Then I wanted to move it in two new files foo.rs and bar.rs.

How do I import/include/use bar.rs from foo.rs?

---

I already read:

• https://doc.rust-lang.org/book/ch07-05-separating-modules-into-different-files.html
• How do I do a basic import/include of a function from one module to another in Rust 2015?
• Split a module across several files
• How to include module from another file from the same project?
• https://doc.rust-lang.org/stable/rust-by-example/mod.html

Neither have the following structure

src/
|-- main.rs
|-- foo.rs
|-- bar.rs

Where foo.rs is trying to use the content of bar.rs.

---

If I try to use a type Bar declared in bar.rs directly from foo.rs, I get:

error[E0433]: failed to resolve: use of undeclared type or module `Bar`
  --> src/foo.rs

---

If I add mod bar at the beginning of foo.rs isn't any better:

error[E0583]: file not found for module `bar`
 --> src/foo.rs
  |
1 | mod bar;
  |     ^^^
  |
  = help: name the file either foo/bar.rs or foo/bar/mod.rs inside the directory "src"

---

And finally (but I wasn't expecting this one to work), with use bar; in foo.rs:

error[E0432]: unresolved import `bar`
 --> src/foo.rs
  |
1 | use bar;
  |     ^^^ no `grammar` external crate

Answer 1

I answered a very similar question here: https://stackoverflow.com/a/76659218/1576548

There's 2 different problems at hand -- there's how to import code from related modules (e.g. a helpers.rs) into your main.rs, but the procedure for doing that is different than importing code from other NON-MAIN modules into other NON-MAIN modules. The example I gave in the aforementioned question uses a.rs, b.rs, and main.rs all in the same directory, where you want to import functions between a.rs and b.rs.