Understanding Rust Error E0583

Rust Error E0583: File not Found for Out-of-line Module

Rust error E0583 occurs when the compiler cannot find a file for an out-of-line module. An out-of-line module is one that is declared in a separate file from the main module.

Example: Error E0583

mod file_that_doesnt_exist; // error: file not found for module

fn main() {}

In the example above, an attempt is made to declare an out-of-line module named 'file_that_doesnt_exist'. However, the compiler cannot find a file named 'file_that_doesnt_exist.rs' or 'file_that_doesnt_exist/mod.rs' in the same directory, and an error E0583 is raised.

How to Resolve Rust Error E0583

To fix this error, ensure a file corresponding to the out-of-line module is present in the same directory. The file should be named according to the following conventions:

1. <module_name>.rs
2. <module_name>/mod.rs

For the erroneous example, you can resolve error E0583 by creating a file named 'file_that_doesnt_exist.rs' or 'file_that_doesnt_exist/mod.rs' in the same directory.

Example: Resolving Error E0583

main.rs
```rust
mod file_that_exists;

fn main() {
    file_that_exists::say_hello();
}
```

file_that_exists.rs
```rust
pub fn say_hello() {
    println!("Hello, world!");
}
```

In the revised example, the 'file_that_exists.rs' file exists in the same directory as 'main.rs', and the 'say_hello()' function is declared in 'file_that_exists.rs'. As a result, the E0583 error is resolved.

Common Causes and Solutions

1. Typo in the module name: Make sure the module name in the 'mod' declaration matches the file's name exactly. 2. Incorrect file path: The module file must be located in the same directory as the main module file. 3. Wrong filename capitalization: Ensure the file's name follows the same capitalization as the module declaration. 4. Forgotten module file: Create a new file for the module if it does not yet exist.