Open
Description
Using the following flags
--force-warn clippy::iter-on-single-items
this code:
use std::option::IntoIter;
fn takes_into_iter(_: impl IntoIterator<Item = i32>) {}
macro_rules! x {
($e:expr) => {
takes_into_iter($e); // lint here because `.into_iter()` is "redundant"
let _: IntoIter<i32> = $e; // removing `.into_iter()` leads to a type error here
};
}
fn main() {
x!(Some(5).into_iter());
}caused the following diagnostics:
Checking _clippy11065-3 v0.1.0 (/tmp/icemaker_global_tempdir.t8dYaH8PqaqW/icemaker_clippyfix_tempdir.S1c809nLp6vL/_clippy11065-3)
warning: `into_iter` call on a collection with only one item
--> src/main.rs:12:8
|
12 | x!(Some(5).into_iter());
| ^^^^^^^^^^^^^^^^^^^ help: try: `std::iter::once(5)`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#iter_on_single_items
= note: requested on the command line with `--force-warn clippy::iter-on-single-items`
warning: `_clippy11065-3` (bin "_clippy11065-3") generated 1 warning
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.11s
However after applying these diagnostics, the resulting code:
use std::option::IntoIter;
fn takes_into_iter(_: impl IntoIterator<Item = i32>) {}
macro_rules! x {
($e:expr) => {
takes_into_iter($e); // lint here because `.into_iter()` is "redundant"
let _: IntoIter<i32> = $e; // removing `.into_iter()` leads to a type error here
};
}
fn main() {
x!(std::iter::once(5));
}no longer compiled:
Checking _clippy11065-3 v0.1.0 (/tmp/icemaker_global_tempdir.t8dYaH8PqaqW/icemaker_clippyfix_tempdir.S1c809nLp6vL/_clippy11065-3)
error[E0308]: mismatched types
--> src/main.rs:12:8
|
7 | let _: IntoIter<i32> = $e; // removing `.into_iter()` leads to a type error here
| ------------- expected due to this
...
12 | x!(std::iter::once(5));
| ^^^^^^^^^^^^^^^^^^ expected `IntoIter<i32>`, found `Once<{integer}>`
|
= note: expected struct `std::option::IntoIter<i32>`
found struct `std::iter::Once<{integer}>`
For more information about this error, try `rustc --explain E0308`.
error: could not compile `_clippy11065-3` (bin "_clippy11065-3") due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `_clippy11065-3` (bin "_clippy11065-3" test) due to 1 previous error
Version:
rustc 1.89.0-nightly (076ec59ff 2025-06-05)
binary: rustc
commit-hash: 076ec59ff1dcf538b9d3a0b8e0d7f4edd0559959
commit-date: 2025-06-05
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.5