Clippy lint · Nursery · checked with Clippy 0.1.99

clippy::significant_drop_tightening: Searches for elements marked with #[clippy::has_significant_drop] that could be early dropped but are in fact dropped at the end of their scopes

What it meansSearches for elements marked with #[clippy::has_significant_drop] that could be early dropped but are in fact dropped at the end of their scopes. In other words, enforces the “tightening” of their possible lifetimes. It is in the nursery group and off by default.

Does it matter?

Elements marked with #[clippy::has_significant_drop] are generally synchronizing primitives that manage shared resources, as such, it is desired to release them as soon as possible to avoid unnecessary resource contention.

New lints still being finished. Off by default and may have false positives.

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

fn main() {
  let lock = some_sync_resource.lock();
  let owned_rslt = lock.do_stuff_with_resource();
  // Only `owned_rslt` is needed but `lock` is still held.
  do_heavy_computation_that_takes_time(owned_rslt);
}

Write this instead

fn main() {
    let owned_rslt = some_sync_resource.lock().do_stuff_with_resource();
    do_heavy_computation_that_takes_time(owned_rslt);
}

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]
significant_drop_tightening = "warn"

In code

#![warn(clippy::significant_drop_tightening)]

One run

cargo clippy -- -W clippy::significant-drop-tightening

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.

Nurserygroup

allowdefault level

nofixed by cargo clippy --fix

1.69.0added in Rust

Clippy's own documentation

What it does

Searches for elements marked with #[clippy::has_significant_drop] that could be early dropped but are in fact dropped at the end of their scopes. In other words, enforces the “tightening” of their possible lifetimes.

Why is this bad?

Elements marked with #[clippy::has_significant_drop] are generally synchronizing primitives that manage shared resources, as such, it is desired to release them as soon as possible to avoid unnecessary resource contention.

Example

fn main() {
  let lock = some_sync_resource.lock();
  let owned_rslt = lock.do_stuff_with_resource();
  // Only `owned_rslt` is needed but `lock` is still held.
  do_heavy_computation_that_takes_time(owned_rslt);
}

Use instead:

fn main() {
    let owned_rslt = some_sync_resource.lock().do_stuff_with_resource();
    do_heavy_computation_that_takes_time(owned_rslt);
}

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

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