clippy::std_instead_of_core: used import from `std` instead of `core`

What you see

warning: used import from `std` instead of `core`
 --> main.rs:3:5
  |
3 | use std::hash::Hasher;
  |     ^^^ help: consider importing the item from `core`: `core`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#std_instead_of_core
  = note: requested on the command line with `-W clippy::std-instead-of-core`

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?

Crates which have no_std compatibility may wish to ensure types are imported from core to ensure disabling std 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 std::hash::Hasher;

Write this instead

use core::hash::Hasher;

Turn it off, or on

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

[lints.clippy]
std_instead_of_core = "warn"

#![warn(clippy::std_instead_of_core)]

cargo clippy -- -W clippy::std-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.