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 https://github.com/rust-lang/rust/issues/121466.
---
*Point at continue and break that might be in the wrong place*
Sometimes move errors are because of a misplaced `continue`, but we didn't
surface that anywhere. Now when there are more than one set of nested loops
we show them out and point at the `continue` and `break` expressions within
that might need to go elsewhere.
```
error[E0382]: use of moved value: `foo`
--> $DIR/nested-loop-moved-value-wrong-continue.rs:46:18
|
LL | for foo in foos {
| ---
| |
| this reinitialization might get skipped
| move occurs because `foo` has type `String`, which does not implement the `Copy` trait
...
LL | for bar in &bars {
| ---------------- inside of this loop
...
LL | baz.push(foo);
| --- value moved here, in previous iteration of loop
...
LL | qux.push(foo);
| ^^^ value used here after move
|
note: verify that your loop breaking logic is correct
--> $DIR/nested-loop-moved-value-wrong-continue.rs:41:17
|
LL | for foo in foos {
| ---------------
...
LL | for bar in &bars {
| ----------------
...
LL | continue;
| ^^^^^^^^ this `continue` advances the loop at line 33
help: consider moving the expression out of the loop so it is only moved once
|
LL ~ let mut value = baz.push(foo);
LL ~ for bar in &bars {
LL |
...
LL | if foo == *bar {
LL ~ value;
|
help: consider cloning the value if the performance cost is acceptable
|
LL | baz.push(foo.clone());
| ++++++++
```
Fix https://github.com/rust-lang/rust/issues/92531.
5608c7f9aa