clippy's automatic fix for map_entry fails to compile, with a borrow error #11935
Description
Summary
I've been doing Advent of Code to learn Rust and I wrote some code which involves counting the appearances of each character in a string. Clippy suggests that I can make the code more efficient by using entry, but the proposed fix fails due to some borrow errors. The proposed fix doesn't work, but I was able to use entry and the compiler's feedback to get some code which does compile.
Reproducer
I tried this code:
let hand = "ABCDABCAA";
let mut counts: HashMap<char, u64> = HashMap::new();
for c in hand.chars() {
if !counts.contains_key(&c) {
counts.insert(c, 1);
} else {
counts.insert(c, counts.get(&c).unwrap() + 1);
}
}I ran cargo clippy --fix and got the following output:
warning: failed to automatically apply fixes suggested by rustc to crate `day_7`
after fixes were automatically applied the compiler reported errors within these files:
* src/day_7.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-clippy/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[E0502]: cannot borrow `counts` as immutable because it is also borrowed as mutable
--> src/day_7.rs:97:34
|
92 | match counts.entry(c) {
| ------ mutable borrow occurs here
...
97 | e.insert(counts.get(&c).unwrap() + 1);
| ------ ^^^^^^ immutable borrow occurs here
| |
| mutable borrow later used by call
error[E0502]: cannot borrow `counts` as immutable because it is also borrowed as mutable
--> src/day_7.rs:199:26
|
194 | match counts.entry(c) {
| ------ mutable borrow occurs here
...
199 | e.insert(counts.get(&c).unwrap() + 1);
| ------ ^^^^^^ immutable borrow occurs here
| |
| mutable borrow later used by call
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0502`.
Original diagnostics will follow.
warning: function `silly` is never used
--> src/day_7.rs:187:4
|
187 | fn silly() {
| ^^^^^
|
= note: `#[warn(dead_code)]` on by default
warning: usage of `contains_key` followed by `insert` on a `HashMap`
--> src/day_7.rs:92:17
|
92 | / if !counts.contains_key(&c) {
93 | | counts.insert(c, 1);
94 | | } else {
95 | | counts.insert(c, counts.get(&c).unwrap() + 1);
96 | | }
| |_________________^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#map_entry
= note: `#[warn(clippy::map_entry)]` on by default
help: try
|
92 ~ match counts.entry(c) {
93 + std::collections::hash_map::Entry::Vacant(e) => {
94 + e.insert(1);
95 + }
96 + std::collections::hash_map::Entry::Occupied(mut e) => {
97 + e.insert(counts.get(&c).unwrap() + 1);
98 + }
99 + }
|
warning: usage of `contains_key` followed by `insert` on a `HashMap`
--> src/day_7.rs:191:9
|
191 | / if !counts.contains_key(&c) {
192 | | counts.insert(c, 1);
193 | | } else {
194 | | counts.insert(c, counts.get(&c).unwrap() + 1);
195 | | }
| |_________^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#map_entry
help: try
|
191 ~ match counts.entry(c) {
192 + std::collections::hash_map::Entry::Vacant(e) => {
193 + e.insert(1);
194 + }
195 + std::collections::hash_map::Entry::Occupied(mut e) => {
196 + e.insert(counts.get(&c).unwrap() + 1);
197 + }
198 + }
|
warning: `all-days` (bin "day_7" test) generated 3 warnings (run `cargo clippy --fix --bin "day_7" --tests` to apply 2 suggestions)
warning: failed to automatically apply fixes suggested by rustc to crate `day_7`
after fixes were automatically applied the compiler reported errors within these files:
* src/day_7.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-clippy/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[E0502]: cannot borrow `counts` as immutable because it is also borrowed as mutable
--> src/day_7.rs:97:34
|
92 | match counts.entry(c) {
| ------ mutable borrow occurs here
...
97 | e.insert(counts.get(&c).unwrap() + 1);
| ------ ^^^^^^ immutable borrow occurs here
| |
| mutable borrow later used by call
error[E0502]: cannot borrow `counts` as immutable because it is also borrowed as mutable
--> src/day_7.rs:199:26
|
194 | match counts.entry(c) {
| ------ mutable borrow occurs here
...
199 | e.insert(counts.get(&c).unwrap() + 1);
| ------ ^^^^^^ immutable borrow occurs here
| |
| mutable borrow later used by call
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0502`.
Original diagnostics will follow.
warning: `all-days` (bin "day_7") generated 3 warnings (3 duplicates)
Version
rustc 1.74.0 (79e9716c9 2023-11-13)
binary: rustc
commit-hash: 79e9716c980570bfd1f666e3b16ac583f0168962
commit-date: 2023-11-13
host: aarch64-apple-darwin
release: 1.74.0
LLVM version: 17.0.4
Additional Labels
No response