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Detect when move of !Copy value occurs within loop and should likely not be cloned

When encountering a move error on a value within a loop of any kind,
identify if the moved value belongs to a call expression that should not
be cloned and avoid the semantically incorrect suggestion. Also try to
suggest moving the call expression outside of the loop instead.

```
error[E0382]: use of moved value: `vec`
  --> $DIR/recreating-value-in-loop-condition.rs:6:33
   |
LL |     let vec = vec!["one", "two", "three"];
   |         --- move occurs because `vec` has type `Vec<&str>`, which does not implement the `Copy` trait
LL |     while let Some(item) = iter(vec).next() {
   |     ----------------------------^^^--------
   |     |                           |
   |     |                           value moved here, in previous iteration of loop
   |     inside of this loop
   |
note: consider changing this parameter type in function `iter` to borrow instead if owning the value isn't necessary
  --> $DIR/recreating-value-in-loop-condition.rs:1:17
   |
LL | fn iter<T>(vec: Vec<T>) -> impl Iterator<Item = T> {
   |    ----         ^^^^^^ this parameter takes ownership of the value
   |    |
   |    in this function
help: consider moving the expression out of the loop so it is only moved once
   |
LL ~     let mut value = iter(vec);
LL ~     while let Some(item) = value.next() {
   |
```

We use the presence of a `break` in the loop that would be affected by
the moved value as a heuristic for "shouldn't be cloned".

Fix #121466.
This commit is contained in:
Esteban Küber 2024-02-26 20:06:19 +00:00
parent 22e241e32e
commit 14473adf42
13 changed files with 437 additions and 42 deletions

View file

@ -2049,7 +2049,7 @@ impl LoopSource {
}
}
#[derive(Copy, Clone, Debug, HashStable_Generic)]
#[derive(Copy, Clone, Debug, PartialEq, HashStable_Generic)]
pub enum LoopIdError {
OutsideLoopScope,
UnlabeledCfInWhileCondition,