Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::empty_drop: empty drop implementation

What it meansChecks for empty Drop implementations. It is in the restriction group and off by default.

What you see

warning: empty drop implementation
 --> main.rs:5:1
  |
5 | / impl Drop for S {
6 | |     fn drop(&mut self) {}
7 | | }
  | |_^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#empty_drop
  = note: requested on the command line with `-W clippy::empty-drop`
  = help: try removing this impl

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?

Empty Drop implementations have no effect when dropping an instance of the type. They are most likely useless. However, an empty Drop implementation prevents a type from being destructured, which might be the intention behind adding the implementation as a marker.

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

How to fix it

Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

struct S;

impl Drop for S {
    fn drop(&mut self) {}
}

Write this instead

struct S;

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
empty_drop = "warn"

In code

#![warn(clippy::empty_drop)]

One run

cargo clippy -- -W clippy::empty-drop

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.

Restrictiongroup

allowdefault level

nofixed by cargo clippy --fix

1.62.0added in Rust

Clippy's own documentation

What it does

Checks for empty Drop implementations.

Why restrict this?

Empty Drop implementations have no effect when dropping an instance of the type. They are most likely useless. However, an empty Drop implementation prevents a type from being destructured, which might be the intention behind adding the implementation as a marker.

Example

struct S;

impl Drop for S {
    fn drop(&mut self) {}
}

Use instead:

struct S;

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

Up next

Also worth your time

Did this answer your question?