Rollup merge of #134977 - estebank:issue-112357, r=BoxyUwU

Detect `mut arg: &Ty` meant to be `arg: &mut Ty` and provide structured suggestion

When a newcomer attempts to use an "out parameter" using borrows, they sometimes get confused and instead of mutating the borrow they try to mutate the function-local binding instead. This leads to either type errors (due to assigning an owned value to a mutable binding of reference type) or a multitude of lifetime errors and unused binding warnings.

This change adds a suggestion to the type error

```
error[E0308]: mismatched types
  --> $DIR/mut-arg-of-borrowed-type-meant-to-be-arg-of-mut-borrow.rs:6:14
   |
LL | fn change_object(mut object: &Object) {
   |                              ------- expected due to this parameter type
LL |     let object2 = Object;
LL |     object = object2;
   |              ^^^^^^^ expected `&Object`, found `Object`
   |
help: you might have meant to mutate the pointed at value being passed in, instead of changing the reference in the local binding
   |
LL ~ fn change_object(object: &mut Object) {
LL |     let object2 = Object;
LL ~     *object = object2;
   |
```
and to the unused assignment lint
```
error: value assigned to `object` is never read
  --> $DIR/mut-arg-of-borrowed-type-meant-to-be-arg-of-mut-borrow.rs:11:5
   |
LL |     object = &object2;
   |     ^^^^^^
   |
note: the lint level is defined here
  --> $DIR/mut-arg-of-borrowed-type-meant-to-be-arg-of-mut-borrow.rs:1:9
   |
LL | #![deny(unused_assignments, unused_variables)]
   |         ^^^^^^^^^^^^^^^^^^
help: you might have meant to mutate the pointed at value being passed in, instead of changing the reference in the local binding
   |
LL ~ fn change_object2(object: &mut Object) {
LL |     let object2 = Object;
LL ~     *object = object2;
   |
```

Fix #112357.

0 files changed, 0 insertions, 0 deletions