Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::forget_non_drop: call to `std::mem::forget` with a value that does not implement `Drop`. Forgetting such a type is the same as dropping it

What it meansChecks for calls to std::mem::forget with a value that does not implement Drop. It is in the suspicious group and warns by default.

What you see

warning: call to `std::mem::forget` with a value that does not implement `Drop`. Forgetting such a type is the same as dropping it
 --> main.rs:5:1
  |
5 | std::mem::forget(x);
  | ^^^^^^^^^^^^^^^^^^^
  |
note: argument has type `main::Foo`
 --> main.rs:5:18
  |
5 | std::mem::forget(x);
  |                  ^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#forget_non_drop
  = note: `#[warn(clippy::forget_non_drop)]` 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?

Calling std::mem::forget is no different than dropping such a type. A different value may have been intended.

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

struct Foo;
let x = Foo;
std::mem::forget(x);

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
forget_non_drop = "allow"

One run

cargo clippy -- -A clippy::forget-non-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.

Suspiciousgroup

warndefault level

nofixed by cargo clippy --fix

1.62.0added in Rust

Clippy's own documentation

What it does

Checks for calls to std::mem::forget with a value that does not implement Drop.

Why is this bad?

Calling std::mem::forget is no different than dropping such a type. A different value may have been intended.

Example

struct Foo;
let x = Foo;
std::mem::forget(x);

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

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