Rollup merge of #41640 - gaurikholkar:master, r=nikomatsakis

Consider changing to & for let bindings #40402

This is a fix for #40402

For the example
```
fn main() {
    let v = vec![String::from("oh no")];

    let e = v[0];
}
```

It gives
```
error[E0507]: cannot move out of indexed content
 --> ex1.rs:4:13
  |
4 |     let e = v[0];
  |             ^^^^ cannot move out of indexed content
  |
  = help: consider changing to `&v[0]`

error: aborting due to previous error
```

Another alternative is
```
error[E0507]: cannot move out of indexed content
 --> ex1.rs:4:13
  |
4 |     let e = v[0];
  |             ^^^^ consider changing to `&v[0]`

error: aborting due to previous error
```
Also refer to #41564 for more details.

r? @nikomatsakis

src/librustc_borrowck/borrowck/gather_loans/move_error.rs

@@ -73,9 +73,16 @@ fn report_move_errors<'a, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>, errors: &Vec<Move
         let mut err = report_cannot_move_out_of(bccx, error.move_from.clone());
         let mut is_first_note = true;
         match error.move_to_places.get(0) {
-            Some(&MovePlace { pat_source: PatternSource::LetDecl(_), .. }) => {
+            Some(&MovePlace { pat_source: PatternSource::LetDecl(ref e), .. }) => {
                 // ignore patterns that are found at the top-level of a `let`;
                 // see `get_pattern_source()` for details
+                let initializer =
+                    e.init.as_ref().expect("should have an initializer to get an error");
+                if let Ok(snippet) = bccx.tcx.sess.codemap().span_to_snippet(initializer.span) {
+                    err.span_suggestion(initializer.span,
+                                        "consider using a reference instead",
+                                        format!("&{}", snippet));
+                }
             }
             _ => {
                 for move_to in &error.move_to_places {

src/test/ui/issue-40402-ref-hints/issue-40402-1.stderr

@@ -2,7 +2,10 @@ error[E0507]: cannot move out of indexed content
   --> $DIR/issue-40402-1.rs:19:13
    |
 19 |     let e = f.v[0];
-   |             ^^^^^^ cannot move out of indexed content
+   |             ^^^^^^
+   |             |
+   |             help: consider using a reference instead `&f.v[0]`
+   |             cannot move out of indexed content
 
 error: aborting due to previous error