FP needless-pass-by-ref-mut with lifetimes #16267
Description
Using the following flags
--force-warn clippy::needless-pass-by-ref-mut
this code:
mod issue11819 {
fn takes_into_iter(_: impl IntoIterator<Item = String>) {}
pub struct MyStruct<T> {
my_field: T,
}
impl<T> MyStruct<T> {
pub fn with_ref<'a>(&'a mut self)
where
&'a T: IntoIterator<Item = String>,
{
takes_into_iter(self.my_field.into_iter());
//~^ useless_conversion
}
pub fn with_ref_mut<'a>(&'a mut self)
where
&'a mut T: IntoIterator<Item = String>,
{
takes_into_iter(self.my_field.into_iter());
//~^ useless_conversion
}
pub fn with_deref<Y>(&mut self)
where
T: std::ops::Deref<Target = Y>,
Y: IntoIterator<Item = String> + Copy,
{
takes_into_iter(self.my_field.into_iter());
//~^ useless_conversion
}
}
}
fn main() {}caused the following diagnostics:
Checking _a v0.1.0 (/tmp/icemaker_global_tempdir.kGLza1WPRM6O/icemaker_clippyfix_tempdir.lVXtr8bw7nRI/_a)
warning: this argument is a mutable reference, but not used mutably
--> src/main.rs:9:29
|
9 | pub fn with_ref<'a>(&'a mut self)
| ^^^^^^^^^^^^ help: consider changing to: `&self`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_ref_mut
= note: requested on the command line with `--force-warn clippy::needless-pass-by-ref-mut`
warning: this argument is a mutable reference, but not used mutably
--> src/main.rs:25:30
|
25 | pub fn with_deref<Y>(&mut self)
| ^^^^^^^^^ help: consider changing to: `&self`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_ref_mut
warning: `_a` (bin "_a") generated 2 warnings
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.22s
However after applying these diagnostics, the resulting code:
mod issue11819 {
fn takes_into_iter(_: impl IntoIterator<Item = String>) {}
pub struct MyStruct<T> {
my_field: T,
}
impl<T> MyStruct<T> {
pub fn with_ref<'a>(&self)
where
&'a T: IntoIterator<Item = String>, T: 'a
{
takes_into_iter(self.my_field.into_iter());
//~^ useless_conversion
}
pub fn with_ref_mut<'a>(&'a mut self)
where
&'a mut T: IntoIterator<Item = String>,
{
takes_into_iter(self.my_field.into_iter());
//~^ useless_conversion
}
pub fn with_deref<Y>(&self)
where
T: std::ops::Deref<Target = Y>,
Y: IntoIterator<Item = String> + Copy,
{
takes_into_iter(self.my_field.into_iter());
//~^ useless_conversion
}
}
}
fn main() {}no longer compiled:
Checking _a v0.1.0 (/tmp/icemaker_global_tempdir.kGLza1WPRM6O/icemaker_clippyfix_tempdir.lVXtr8bw7nRI/_a)
error: lifetime may not live long enough
--> src/main.rs:13:29
|
9 | pub fn with_ref<'a>(&self)
| -- - let's call the lifetime of this reference `'1`
| |
| lifetime `'a` defined here
...
13 | takes_into_iter(self.my_field.into_iter());
| ^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'1` must outlive `'a`
error: could not compile `_a` (bin "_a" test) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `_a` (bin "_a") due to 1 previous error
Version:
rustc 1.94.0-nightly (806c2a35d 2025-12-19)
binary: rustc
commit-hash: 806c2a35dcc1db7867864fea0a7a65554a5238b7
commit-date: 2025-12-19
host: x86_64-unknown-linux-gnu
release: 1.94.0-nightly
LLVM version: 21.1.8