Rust modules structure in a nutshell

Rust module structure in a nutshell.

File tree:

.
├── Cargo.lock
├── Cargo.toml
├── src
│   ├── main.rs
│   ├── my_modules_in_rootdir.rs
│   ├── my_modules_with_modrs
│   │   ├── mod.rs
│   │   ├── submod_a.rs
│   │   └── submod_b.rs
│   ├── my_modules_without_modrs
│   │   ├── submod_1.rs
│   │   └── submod_2.rs
│   └── my_modules_without_modrs.rs
\

Module tree (this nice module tree is generated by cargo-modules)

crate modules
├── mod my_module_in_main: pub(crate)
│   └── mod my_mod_in_main_nested: pub
├── mod my_modules_in_rootdir: pub(crate)
├── mod my_modules_with_modrs: pub(crate)
│   ├── mod submod_a: pub
│   └── mod submod_b: pub
└── mod my_modules_without_modrs: pub(crate)
    ├── mod submod_1: pub
    └── mod submod_2: pub

/src/main.rs

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#![allow(dead_code)]
// declare module in the root dir, so that this module is added to the
// module tree
mod my_modules_in_rootdir; 
mod my_modules_with_modrs;
mod my_modules_without_modrs;
mod my_module_in_main {
    // DESCRIPTION IS PRIVATE TO my_mod
    const DESCRIPTION: &str = "This module is defined as `mod my_mod_in_main{{...}}` in main.rs";
    pub fn desc() {
       println!("{}", DESCRIPTION);
    }
    }
    pub mod my_mod_in_main_nested {
        // DESCRIPTION PRIVATE TO my_mod::my_mod_nested
        const DESCRIPTION: &str = "This module is defined as a nested mod in my_mod_in_main` in main.rs";
        pub fn desc() {
           println!("{}", DESCRIPTION);
        }
    }
}

fn main() {
    println!("Hello, world from main()");
    my_module_in_main::desc();
    my_module_in_main::my_mod_in_main_nested::desc();
    my_modules_in_rootdir::desc();
    my_modules_with_modrs::desc();
    my_modules_with_modrs::submod_a::desc();
    my_modules_with_modrs::submod_b::desc();
    my_modules_without_modrs::submod_1::desc();
    my_modules_without_modrs::submod_2::desc();
}

/src/my_modules_in_rootdir

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const DESCRIPTION: &str = "This module is defined in src/my_modules_in_rootdir.rs, and declared in main.rs";
pub fn desc() {
    println!("{}", DESCRIPTION);
}

/src/my_modules_without_modrs.rs

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// This is bad, you need this file in root dir to declare the module into the module tree anyways,
// why don't you just move this file to somemodule/mod.rs ?? 
pub mod submod_1;
pub mod submod_2;

/src/my_modules_without_modrs/submod_1.rs

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const DESCRIPTION: &str = "This module is /src/my_modules_without_modrs/submod_1, module declared in /src/my_modules_without_modrs.rs";
pub fn desc() {
    println!("{}", DESCRIPTION);
}

/src/my_modules_without_modrs/submod_2.rs

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const DESCRIPTION: &str = "This module is /src/my_modules_without_modrs/submod_2, module declared in /src/my_modules_without_modrs.rs";
pub fn desc() {
    println!("{}", DESCRIPTION);
}

/src/my_modules_with_modrs/mod.rs

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pub mod submod_a;
pub mod submod_b;

const DESCRIPTION: &str = "This module is /src/my_modules_with_modrs, function declared in mod.rs";
pub fn desc() {
    println!("{}", DESCRIPTION);
}

/src/my_modules_with_modrs/submod_a.rs

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const DESCRIPTION: &str = "This module is /src/my_modules_with_modrs/submod_a, module declared in mod.rs";
pub fn desc() {
    println!("{}", DESCRIPTION);
}

/src/my_modules_with_modrs/submod_b.rs

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const DESCRIPTION: &str = "This module is /src/my_modules_with_modrs/submod_b, module declared in mod.rs";
pub fn desc() {
    println!("{}", DESCRIPTION);
}