Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::duplicate_mod: file is loaded as a module multiple times: `main.rs`

What it meansChecks for files that are included as modules multiple times. It is in the suspicious group and warns by default.

What you see

warning: file is loaded as a module multiple times: `main.rs`
 --> main.rs:4:1
  |
4 | mod a;
  | ^^^^^^ first loaded here
5 | mod b;
  | ^^^^^^ loaded again here
  |
  = help: replace all but one `mod` item with `use` items
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#duplicate_mod
  = note: `#[warn(clippy::duplicate_mod)]` on by default

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

Loading a file as a module more than once causes it to be compiled multiple times, taking longer and putting duplicate content into the module tree.

Code that is most likely wrong or useless. Warns by default.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

// lib.rs
mod a;
mod b;

Write this instead

// a.rs
#[path = "./b.rs"]
mod b;

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::duplicate_mod)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
duplicate_mod = "allow"

One run

cargo clippy -- -A clippy::duplicate-mod

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.

Suspiciousgroup

warndefault level

nofixed by cargo clippy --fix

1.63.0added in Rust

Clippy's own documentation

What it does

Checks for files that are included as modules multiple times.

Why is this bad?

Loading a file as a module more than once causes it to be compiled multiple times, taking longer and putting duplicate content into the module tree.

Example

// lib.rs
mod a;
mod b;

// a.rs
#[path = "./b.rs"]
mod b;

Use instead:

// lib.rs
mod a;
mod b;

// a.rs
use crate::b;

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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