Clippy incorrectly reports redundant imported items

[Robbepop]

Summary

For my crate wasmi_core in https://github.com/wasmi-labs/wasmi/tree/master/crates/core I see the following warnings when running clippy on nightly channel:

warning: the item `Box` is imported redundantly
   --> crates/wasmi/src/store.rs:32:5
    |
32  | use alloc::boxed::Box;
    |     ^^^^^^^^^^^^^^^^^
    |
   ::: /Users/robin/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/std/src/prelude/mod.rs:125:13
    |
125 |     pub use super::v1::*;
    |             --------- the item `Box` is already defined here

Many more warnings pop up, but they all are very similar to the one above.
This import is required for proper no_std builds.

In lib.rs we do:

#[cfg(not(feature = "std"))]
extern crate alloc;

Thus alloc is always available as crate root import.

Lint Name

unused_imports

Reproducer

• Clone the repository https://github.com/wasmi-labs/wasmi (rev = a2f299af2f97af3691e195a4473abaa93bca72f7)
• Install clippy from current nightly channel. (I use clippy 0.1.78 (ef324565 2024-02-27))
• Run cargo +nightly clippy -p wasmi_core

Version

rustc 1.78.0-nightly (ef324565d 2024-02-27)
binary: rustc
commit-hash: ef324565d071c6d7e2477a195648549e33d6a465
commit-date: 2024-02-27
host: aarch64-apple-darwin
release: 1.78.0-nightly
LLVM version: 18.1.0

Additional Labels

No response

[Alexendoo]

This is from rustc so you'd see the same with a cargo check, the lint was expanded to cover more cases - rust-lang/rust#117772

The code is evaluated with the std feature enabled where the import is redundant, but cfging every time you import Vec from alloc is understandably a hassle. It would be worth bringing up in rust-lang/rust#121708 this use case for wanting to disable the redundant import warnings