Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::alloc_instead_of_core: Finds items imported through alloc when available through core

What it meansFinds items imported through alloc when available through core. It is in the restriction group and off by default.

Does it matter?

Crates which have no_std compatibility and may optionally require alloc may wish to ensure types are imported from core to ensure disabling alloc does not cause the crate to fail to compile. This lint is also useful for crates migrating to become no_std compatible.

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 can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.

Flagged

use alloc::slice::from_ref;

Write this instead

use core::slice::from_ref;

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]
alloc_instead_of_core = "warn"

In code

#![warn(clippy::alloc_instead_of_core)]

One run

cargo clippy -- -W clippy::alloc-instead-of-core

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

yesfixed by cargo clippy --fix

1.64.0added in Rust

Clippy's own documentation

What it does

Finds items imported through alloc when available through core.

Why restrict this?

Crates which have no_std compatibility and may optionally require alloc may wish to ensure types are imported from core to ensure disabling alloc does not cause the crate to fail to compile. This lint is also useful for crates migrating to become no_std compatible.

Known problems

The lint is only partially aware of the required MSRV for items that were originally in std but moved to core.

Example

use alloc::slice::from_ref;

Use instead:

use core::slice::from_ref;

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

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