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Improve the suggestion for useless_conversion #14864

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d2863e3
add test for issue#14847
donkomura May 21, 2025
76b90dc
resolve deref at adjustments
donkomura May 21, 2025
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15 changes: 14 additions & 1 deletion clippy_lints/src/useless_conversion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -459,5 +459,18 @@ fn adjustments(cx: &LateContext<'_>, expr: &Expr<'_>) -> String {
_ => {},
}
}
prefix
resolve_deref(prefix)
}

fn resolve_deref(mut s: String) -> String {
loop {
if let Some(rest) = s.strip_prefix("&*") {
s = rest.to_string();
} else if let Some(rest) = s.strip_prefix("&*mut ") {
s = format!("mut {rest}");
} else {
break;
}
}
s
}
9 changes: 9 additions & 0 deletions tests/ui/useless_conversion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -175,9 +175,18 @@ fn main() {
let _ = vec![s4, s4, s4].into_iter().into_iter();
//~^ useless_conversion

issue14847();
issue11300::bar();
}

fn issue14847() {
use std::option::IntoIter;
fn takes_into_iter<'a>(_: impl IntoIterator<Item = &'a i32>) {}

let x = &&[1];
let _ = takes_into_iter(x.into_iter());
}

#[allow(dead_code)]
fn issue11065_fp() {
use std::option::IntoIter;
Expand Down
122 changes: 77 additions & 45 deletions tests/ui/useless_conversion.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -118,188 +118,223 @@ error: useless conversion to the same type: `std::vec::IntoIter<Foo<'a'>>`
LL | let _ = vec![s4, s4, s4].into_iter().into_iter();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into_iter()`: `vec![s4, s4, s4].into_iter()`

error: this let-binding has unit value
--> tests/ui/useless_conversion.rs:187:5
|
LL | let _ = takes_into_iter(x.into_iter());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: omit the `let` binding: `takes_into_iter(x.into_iter());`
|
= note: `-D clippy::let-unit-value` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(clippy::let_unit_value)]`

error: this `.into_iter()` call is equivalent to `.iter()` and will not consume the `array`
--> tests/ui/useless_conversion.rs:187:31
|
LL | let _ = takes_into_iter(x.into_iter());
| ^^^^^^^^^ help: call directly: `iter`
|
= note: `-D clippy::into-iter-on-ref` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(clippy::into_iter_on_ref)]`

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:187:29
|
LL | let _ = takes_into_iter(x.into_iter());
| ^^^^^^^^^^^^^
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:184:36
|
LL | fn takes_into_iter<'a>(_: impl IntoIterator<Item = &'a i32>) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: consider removing the `.into_iter()`
|
LL - let _ = takes_into_iter(x.into_iter());
LL + let _ = takes_into_iter(*x);
|

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:208:7
--> tests/ui/useless_conversion.rs:217:7
|
LL | b(vec![1, 2].into_iter());
| ^^^^^^^^^^------------
| |
| help: consider removing the `.into_iter()`
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:198:13
--> tests/ui/useless_conversion.rs:207:13
|
LL | fn b<T: IntoIterator<Item = i32>>(_: T) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:210:7
--> tests/ui/useless_conversion.rs:219:7
|
LL | c(vec![1, 2].into_iter());
| ^^^^^^^^^^------------
| |
| help: consider removing the `.into_iter()`
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:199:18
--> tests/ui/useless_conversion.rs:208:18
|
LL | fn c(_: impl IntoIterator<Item = i32>) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:212:7
--> tests/ui/useless_conversion.rs:221:7
|
LL | d(vec![1, 2].into_iter());
| ^^^^^^^^^^------------
| |
| help: consider removing the `.into_iter()`
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:202:12
--> tests/ui/useless_conversion.rs:211:12
|
LL | T: IntoIterator<Item = i32>,
| ^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:216:7
--> tests/ui/useless_conversion.rs:225:7
|
LL | b(vec![1, 2].into_iter().into_iter());
| ^^^^^^^^^^------------------------
| |
| help: consider removing the `.into_iter()`s
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:198:13
--> tests/ui/useless_conversion.rs:207:13
|
LL | fn b<T: IntoIterator<Item = i32>>(_: T) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:218:7
--> tests/ui/useless_conversion.rs:227:7
|
LL | b(vec![1, 2].into_iter().into_iter().into_iter());
| ^^^^^^^^^^------------------------------------
| |
| help: consider removing the `.into_iter()`s
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:198:13
--> tests/ui/useless_conversion.rs:207:13
|
LL | fn b<T: IntoIterator<Item = i32>>(_: T) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:265:24
--> tests/ui/useless_conversion.rs:274:24
|
LL | foo2::<i32, _>([1, 2, 3].into_iter());
| ^^^^^^^^^------------
| |
| help: consider removing the `.into_iter()`
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:244:12
--> tests/ui/useless_conversion.rs:253:12
|
LL | I: IntoIterator<Item = i32> + Helper<X>,
| ^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:274:14
--> tests/ui/useless_conversion.rs:283:14
|
LL | foo3([1, 2, 3].into_iter());
| ^^^^^^^^^------------
| |
| help: consider removing the `.into_iter()`
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:253:12
--> tests/ui/useless_conversion.rs:262:12
|
LL | I: IntoIterator<Item = i32>,
| ^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:284:16
--> tests/ui/useless_conversion.rs:293:16
|
LL | S1.foo([1, 2].into_iter());
| ^^^^^^------------
| |
| help: consider removing the `.into_iter()`
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:281:27
--> tests/ui/useless_conversion.rs:290:27
|
LL | pub fn foo<I: IntoIterator>(&self, _: I) {}
| ^^^^^^^^^^^^

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:304:44
--> tests/ui/useless_conversion.rs:313:44
|
LL | v0.into_iter().interleave_shortest(v1.into_iter());
| ^^------------
| |
| help: consider removing the `.into_iter()`
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:291:20
--> tests/ui/useless_conversion.rs:300:20
|
LL | J: IntoIterator,
| ^^^^^^^^^^^^

error: useless conversion to the same type: `()`
--> tests/ui/useless_conversion.rs:332:58
--> tests/ui/useless_conversion.rs:341:58
|
LL | let _: Result<(), std::io::Error> = test_issue_3913().map(Into::into);
| ^^^^^^^^^^^^^^^^ help: consider removing

error: useless conversion to the same type: `std::io::Error`
--> tests/ui/useless_conversion.rs:335:58
--> tests/ui/useless_conversion.rs:344:58
|
LL | let _: Result<(), std::io::Error> = test_issue_3913().map_err(Into::into);
| ^^^^^^^^^^^^^^^^^^^^ help: consider removing

error: useless conversion to the same type: `()`
--> tests/ui/useless_conversion.rs:338:58
--> tests/ui/useless_conversion.rs:347:58
|
LL | let _: Result<(), std::io::Error> = test_issue_3913().map(From::from);
| ^^^^^^^^^^^^^^^^ help: consider removing

error: useless conversion to the same type: `std::io::Error`
--> tests/ui/useless_conversion.rs:341:58
--> tests/ui/useless_conversion.rs:350:58
|
LL | let _: Result<(), std::io::Error> = test_issue_3913().map_err(From::from);
| ^^^^^^^^^^^^^^^^^^^^ help: consider removing

error: useless conversion to the same type: `()`
--> tests/ui/useless_conversion.rs:345:31
--> tests/ui/useless_conversion.rs:354:31
|
LL | let _: ControlFlow<()> = c.map_break(Into::into);
| ^^^^^^^^^^^^^^^^^^^^^^ help: consider removing

error: useless conversion to the same type: `()`
--> tests/ui/useless_conversion.rs:349:31
--> tests/ui/useless_conversion.rs:358:31
|
LL | let _: ControlFlow<()> = c.map_continue(Into::into);
| ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing

error: useless conversion to the same type: `u32`
--> tests/ui/useless_conversion.rs:363:41
--> tests/ui/useless_conversion.rs:372:41
|
LL | let _: Vec<u32> = [1u32].into_iter().map(Into::into).collect();
| ^^^^^^^^^^^^^^^^ help: consider removing

error: useless conversion to the same type: `T`
--> tests/ui/useless_conversion.rs:374:18
--> tests/ui/useless_conversion.rs:383:18
|
LL | x.into_iter().map(Into::into).collect()
| ^^^^^^^^^^^^^^^^ help: consider removing

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:390:29
--> tests/ui/useless_conversion.rs:399:29
|
LL | takes_into_iter(self.my_field.into_iter());
| ^^^^^^^^^^^^^^^^^^^^^^^^^
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:379:32
--> tests/ui/useless_conversion.rs:388:32
|
LL | fn takes_into_iter(_: impl IntoIterator<Item = String>) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
Expand All @@ -310,13 +345,13 @@ LL + takes_into_iter(&self.my_field);
|

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:398:29
--> tests/ui/useless_conversion.rs:407:29
|
LL | takes_into_iter(self.my_field.into_iter());
| ^^^^^^^^^^^^^^^^^^^^^^^^^
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:379:32
--> tests/ui/useless_conversion.rs:388:32
|
LL | fn takes_into_iter(_: impl IntoIterator<Item = String>) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
Expand All @@ -327,13 +362,13 @@ LL + takes_into_iter(&mut self.my_field);
|

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:407:29
--> tests/ui/useless_conversion.rs:416:29
|
LL | takes_into_iter(self.my_field.into_iter());
| ^^^^^^^^^^^^^^^^^^^^^^^^^
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:379:32
--> tests/ui/useless_conversion.rs:388:32
|
LL | fn takes_into_iter(_: impl IntoIterator<Item = String>) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
Expand All @@ -344,30 +379,27 @@ LL + takes_into_iter(*self.my_field);
|

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:416:29
--> tests/ui/useless_conversion.rs:425:29
|
LL | takes_into_iter(self.my_field.into_iter());
| ^^^^^^^^^^^^^^^^^^^^^^^^^
| ^^^^^^^^^^^^^------------
| |
| help: consider removing the `.into_iter()`
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:379:32
--> tests/ui/useless_conversion.rs:388:32
|
LL | fn takes_into_iter(_: impl IntoIterator<Item = String>) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: consider removing the `.into_iter()`
|
LL - takes_into_iter(self.my_field.into_iter());
LL + takes_into_iter(&*self.my_field);
|

error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> tests/ui/useless_conversion.rs:425:29
--> tests/ui/useless_conversion.rs:434:29
|
LL | takes_into_iter(self.my_field.into_iter());
| ^^^^^^^^^^^^^^^^^^^^^^^^^
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> tests/ui/useless_conversion.rs:379:32
--> tests/ui/useless_conversion.rs:388:32
|
LL | fn takes_into_iter(_: impl IntoIterator<Item = String>) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
Expand All @@ -378,16 +410,16 @@ LL + takes_into_iter(&mut *self.my_field);
|

error: useless conversion to the same type: `std::ops::Range<u32>`
--> tests/ui/useless_conversion.rs:440:5
--> tests/ui/useless_conversion.rs:449:5
|
LL | R.into_iter().for_each(|_x| {});
| ^^^^^^^^^^^^^ help: consider removing `.into_iter()`: `R`

error: useless conversion to the same type: `std::ops::Range<u32>`
--> tests/ui/useless_conversion.rs:442:13
--> tests/ui/useless_conversion.rs:451:13
|
LL | let _ = R.into_iter().map(|_x| 0);
| ^^^^^^^^^^^^^ help: consider removing `.into_iter()`: `R`

error: aborting due to 43 previous errors
error: aborting due to 46 previous errors

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