Detect when move of !Copy value occurs within loop and should likely not be cloned #121652

…ely 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 rust-lang#121466.

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 rust-lang#92531.

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Detect when move of !Copy value occurs within loop and should likely not be cloned #121652

Detect when move of !Copy value occurs within loop and should likely not be cloned #121652

Commits on Mar 17, 2024