Repository navigation
FP unnecessary_fold: no longer able to infer type #10000
Description
Summary
.
Lint Name
unnecessary_fold
Reproducer
I tried this code:
use std::collections::HashMap;
use std::hash::BuildHasher;
fn smoketest_map<S: BuildHasher>(mut map: HashMap<i32, i32, S>) {
map.insert(0, 0);
assert_eq!(map.values().fold(0, |x, y| x + y), 0);
}
fn main() {
smoketest_map(HashMap::new());
}I saw this happen:
after fixes were automatically applied the compiler reported errors within these files:
* src/main.rs
This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag
The following errors were reported:
error[E0283]: type annotations needed
--> src/main.rs:6:29
|
6 | assert_eq!(map.values().sum(), 0);
| ^^^ cannot infer type of the type parameter `S` declared on the associated function `sum`
|
= note: cannot satisfy `_: std::iter::Sum<&i32>`
note: required by a bound in `std::iter::Iterator::sum`
--> /home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:3379:12
|
3379 | S: Sum<Self::Item>,
| ^^^^^^^^^^^^^^^ required by this bound in `std::iter::Iterator::sum`
help: consider specifying the type argument in the function call
|
6 | assert_eq!(map.values().sum::<S>(), 0);
| +++++
error: aborting due to previous error
For more information about this error, try `rustc --explain E0283`.
Original diagnostics will follow.
warning: this `.fold` can be written more succinctly using another method
--> src/main.rs:6:29
|
6 | assert_eq!(map.values().fold(0, |x, y| x + y), 0);
| ^^^^^^^^^^^^^^^^^^^^^ help: try: `sum()`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_fold
= note: `#[warn(clippy::unnecessary_fold)]` on by default
Version
rustc 1.67.0-nightly (e0098a5cc 2022-11-29)
binary: rustc
commit-hash: e0098a5cc3a87d857e597af824d0ce1ed1ad85e0
commit-date: 2022-11-29
host: x86_64-unknown-linux-gnu
release: 1.67.0-nightly
LLVM version: 15.0.4
Additional Labels
No response
Activity
Auto merge of #10931 - y21:issue10000, r=Jarcho