Rollup merge of #37405 - mikhail-m1:dnlle, r=jonathandturner

Improve "Doesn't live long enough" error

case with different lifetime scope

issue #36537 part of #35233
r? @jonathandturner

Author: Jonathan Turner

src/librustc_borrowck/borrowck/mod.rs

@@ -1064,6 +1064,19 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
                         db.note("values in a scope are dropped in the opposite order \
                                 they are created");
                     }
+                    (Some(s1), Some(s2)) if !is_temporary && !is_closure => {
+                        db.span = MultiSpan::from_span(s2);
+                        db.span_label(error_span, &format!("borrow occurs here"));
+                        let msg = match opt_loan_path(&err.cmt) {
+                            None => "borrowed value".to_string(),
+                            Some(lp) => {
+                                format!("`{}`", self.loan_path_to_string(&lp))
+                            }
+                        };
+                        db.span_label(s2,
+                                      &format!("{} dropped here while still borrowed", msg));
+                        db.span_label(s1, &format!("{} needs to live until here", value_kind));
+                    }
                     _ => {
                         match sub_span {
                             Some(s) => {

src/test/compile-fail/borrowck/borrowck-ref-into-rvalue.rs renamed to src/test/ui/span/borrowck-ref-into-rvalue.rs

@@ -0,0 +1,16 @@
+error: borrowed value does not live long enough
+  --> $DIR/borrowck-ref-into-rvalue.rs:18:5
+   |
+14 |         Some(ref m) => { //~ ERROR borrowed value does not live long enough
+   |              ----- borrow occurs here
+...
+18 |     }
+   |     ^ borrowed value dropped here while still borrowed
+19 |     println!("{}", *msg);
+20 | }
+   | - borrowed value needs to live until here
+   |
+   = note: consider using a `let` binding to increase its lifetime
+
+error: aborting due to previous error
+

src/test/ui/span/borrowck-ref-into-rvalue.stderr

@@ -0,0 +1,12 @@
+error: `*a` does not live long enough
+  --> $DIR/destructor-restrictions.rs:19:5
+   |
+18 |         *a.borrow() + 1    //~ ERROR `*a` does not live long enough
+   |          - borrow occurs here
+19 |     };
+   |     ^- borrowed value needs to live until here
+   |     |
+   |     `*a` dropped here while still borrowed
+
+error: aborting due to previous error
+

src/test/compile-fail/destructor-restrictions.rs renamed to src/test/ui/span/destructor-restrictions.rs

@@ -4,8 +4,8 @@ error: `x` does not live long enough
 18 |         let f = to_fn_once(move|| &x);
    |                                    ^
    |                                    |
-   |                                    does not live long enough
-   |                                    borrowed value only lives until here
+   |                                    borrow occurs here
+   |                                    `x` dropped here while still borrowed
 ...
 23 | }
    | - borrowed value needs to live until here

src/test/ui/span/destructor-restrictions.stderr

@@ -9,14 +9,14 @@ error: `y` does not live long enough
    = note: values in a scope are dropped in the opposite order they are created
 
 error: `y` does not live long enough
-  --> $DIR/issue-23338-locals-die-before-temps-of-body.rs:27:9
+  --> $DIR/issue-23338-locals-die-before-temps-of-body.rs:28:5
    |
 27 |         y.borrow().clone() //~ ERROR `y` does not live long enough
-   |         ^ does not live long enough
+   |         - borrow occurs here
 28 |     };
-   |     -- borrowed value needs to live until here
+   |     ^- borrowed value needs to live until here
    |     |
-   |     borrowed value only lives until here
+   |     `y` dropped here while still borrowed
 
 error: aborting due to 2 previous errors
 

src/test/ui/span/issue-11925.stderr

@@ -0,0 +1,12 @@
+error: `b` does not live long enough
+  --> $DIR/mut-ptr-cant-outlive-ref.rs:19:5
+   |
+18 |         p = &*b; //~ ERROR `b` does not live long enough
+   |               - borrow occurs here
+19 |     }
+   |     ^ `b` dropped here while still borrowed
+20 | }
+   | - borrowed value needs to live until here
+
+error: aborting due to previous error
+