Rust: Can't import 1 module from 2 files

Question

This is my file structure:

src/
├── main.rs
├── args_parser.rs
└── trim.rs

In args_parser.rs I have enum Args that I want to use in main.rs and in trim.rs, but when trying to run trim.rs with mod args_parser; at the beginning it spits out this error message:

error[E0583]: file not found for module `args_parser`
 --> src/trim.rs:1:5
  |
1 | mod args_parser;
  |     ^^^^^^^^^^^
  |
  = help: name the file either trim/args_parser.rs or trim/args_parser/mod.rs inside the directory "src"

It seems like it expects trim.rs to import only files that are from this module, but in Rust by example (https://doc.rust-lang.org/rust-by-example/mod/split.html) it says "This declaration will look for a file named my.rs or my/mod.rs".

Is there any way I can import this file from main.rs and from trim.rs?

Answer 1

You seem to be mixing up declaring a module (mod <name>) and importing a module (use <name>). The mod keyword is used to declare a new module, either in another file, or with curly braces immediately following the keyword. You can then import the module with use.

When using mod to declare a module in another file, it looks in specific locations. For example, when you use the following statement in main.rs, mod.rs, or lib.rs...

mod abc;

...the compiler will search for contents of the module in ./abc.rs and abc/mod.rs. However, if I have the same statement in a different file, like def.rs, it will instead check in def/abc.rs and def/abc/mod.rs. This is why your code isn't compiling.

To fix this, declare the module in your main file, and then import it elsewhere. This is what the code would look like:

// in main.rs
mod args_parser;
mod trim;
use args_parser::...; // use whatever you need in main

// in trim.rs
use crate::args_parser::...; // use whatever you need in trim - note the crate:: prefix