Provide more context and suggestions in borrowck errors involving closures #124136

Start pointing to where bindings were declared when they are captured in closures: ``` error[E0597]: `x` does not live long enough --> $DIR/suggest-return-closure.rs:23:9 | LL | let x = String::new(); | - binding `x` declared here ... LL | |c| { | --- value captured here LL | x.push(c); | ^ borrowed value does not live long enough ... LL | } | -- borrow later used here | | | `x` dropped here while still borrowed ``` Suggest cloning in more cases involving closures: ``` error[E0507]: cannot move out of `foo` in pattern guard --> $DIR/issue-27282-move-ref-mut-into-guard.rs:11:19 | LL | if { (|| { let mut bar = foo; bar.take() })(); false } => {}, | ^^ --- move occurs because `foo` has type `&mut Option<&i32>`, which does not implement the `Copy` trait | | | `foo` is moved here | = note: variables bound in patterns cannot be moved from until after the end of the pattern guard help: consider cloning the value if the performance cost is acceptable | LL | if { (|| { let mut bar = foo.clone(); bar.take() })(); false } => {}, | ++++++++ ```

``` error[E0382]: use of moved value: `t` --> $DIR/use_of_moved_value_copy_suggestions.rs:7:9 | LL | fn duplicate_t<T>(t: T) -> (T, T) { | - move occurs because `t` has type `T`, which does not implement the `Copy` trait ... LL | (t, t) | - ^ value used here after move | | | value moved here | help: if `T` implemented `Clone`, you could clone the value --> $DIR/use_of_moved_value_copy_suggestions.rs:4:16 | LL | fn duplicate_t<T>(t: T) -> (T, T) { | ^ consider constraining this type parameter with `Clone` ... LL | (t, t) | - you could clone this value help: consider restricting type parameter `T` | LL | fn duplicate_t<T: Copy>(t: T) -> (T, T) { | ++++++ ``` The `help` is new. On ADTs, we also extend the output with span labels: ``` error[E0507]: cannot move out of static item `FOO` --> $DIR/issue-17718-static-move.rs:6:14 | LL | let _a = FOO; | ^^^ move occurs because `FOO` has type `Foo`, which does not implement the `Copy` trait | note: if `Foo` implemented `Clone`, you could clone the value --> $DIR/issue-17718-static-move.rs:1:1 | LL | struct Foo; | ^^^^^^^^^^ consider implementing `Clone` for this type ... LL | let _a = FOO; | --- you could clone this value help: consider borrowing here | LL | let _a = &FOO; | + ```

``` error[E0507]: cannot move out of `bar`, a captured variable in an `FnMut` closure --> $DIR/borrowck-move-by-capture.rs:9:29 | LL | let bar: Box<_> = Box::new(3); | --- captured outer variable LL | let _g = to_fn_mut(|| { | -- captured by this `FnMut` closure LL | let _h = to_fn_once(move || -> isize { *bar }); | ^^^^^^^^^^^^^^^^ ---- | | | | | variable moved due to use in closure | | move occurs because `bar` has type `Box<isize>`, which does not implement the `Copy` trait | `bar` is moved here | help: clone the value before moving it into the closure | LL ~ let value = bar.clone(); LL ~ let _h = to_fn_once(move || -> isize { value }); | ```

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Provide more context and suggestions in borrowck errors involving closures #124136

Provide more context and suggestions in borrowck errors involving closures #124136

Commits on Apr 24, 2024