FP redundant_clone: Box

Summary

.

Lint Name

redundant_clone

Reproducer

I tried this code:

pub fn main() {
    let i: Box<_> = Box::new(1);
    let j = i.clone();
    assert_eq!(*i, 2);
}

I saw this happen:

warning: redundant clone
 --> unique-decl-init-copy.rs:3:14
  |
3 |     let j = i.clone();
  |              ^^^^^^^^ help: remove this
  |
note: cloned value is neither consumed nor mutated
 --> unique-decl-init-copy.rs:3:13
  |
3 |     let j = i.clone();
  |             ^^^^^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_clone
  = note: `#[warn(clippy::redundant_clone)]` on by defaul

But

pub fn main() {
    let i: Box<_> = Box::new(1);
    let j = i;
    assert_eq!(*i, 2);
}

does not compile

warning: unused variable: `j`
 --> unique-decl-init-copy.rs:3:9
  |
3 |     let j = i;
  |         ^ help: if this is intentional, prefix it with an underscore: `_j`
  |
  = note: `#[warn(unused_variables)]` on by default

error[E0382]: borrow of moved value: `i`
 --> unique-decl-init-copy.rs:4:5
  |
2 |     let i: Box<_> = Box::new(1);
  |         - move occurs because `i` has type `std::boxed::Box<i32>`, which does not implement the `Copy` trait
3 |     let j = i;
  |             - value moved here
4 |     assert_eq!(*i, 2);
  |     ^^^^^^^^^^^^^^^^^ value borrowed here after move
  |
  = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider cloning the value if the performance cost is acceptable
  |
3 |     let j = i.clone();
  |              ++++++++

error: aborting due to previous error; 1 warning emitted

Version

rustc 1.70.0-nightly (511364e78 2023-03-16)
binary: rustc
commit-hash: 511364e7874dba9649a264100407e4bffe7b5425
commit-date: 2023-03-16
host: x86_64-unknown-linux-gnu
release: 1.70.0-nightly
LLVM version: 15.0.7

Additional Labels

No response

Start by locating the redundant_clone lint implementation and its tests in the Clippy repository, then run the supplied Box reproducer. Trace why the lint treats the clone as redundant even though the original value is used afterward, and add coverage showing the warning is not emitted for this case.