rust-modern-modules

name	rust-modern-modules
description	Enforce modern Rust module file layout. Use when Codex creates, splits, moves, or refactors Rust modules, especially when deciding between `mod.rs` and `foo.rs` plus `foo/bar.rs` layouts.

Rust Modern Modules

Rule

Prefer Rust 2018+ module layout:

src/foo.rs
src/foo/bar.rs

Use this from src/foo.rs:

mod bar;

Do not create src/foo/mod.rs for new modules unless the repository already consistently uses mod.rs in that area or the user explicitly asks for it.

Workflow

1. Inspect nearby Rust modules before creating files.
2. If both layouts are viable, choose foo.rs as the parent module and foo/*.rs for children.
3. If refactoring an existing mod.rs, avoid moving it unless the user asked for a layout cleanup or the move is necessary for the task.
4. Keep module declarations private by default: use mod child; first, then widen to pub mod child; only when external access is needed.
5. Run cargo fmt after moving or creating Rust module files.

Examples

For a logging module with a daily appender, prefer:

src/logging.rs
src/logging/daily_file_appender.rs

Inside src/logging.rs:

mod daily_file_appender;

use daily_file_appender::DailyFileAppender;