Auto merge of #54088 - matthewjasper:use-reason-in-dlle-errors, r=pnkfelix

[NLL] Suggest let binding

Closes #49821

Also adds an alternative to `explain_why_borrow_contains_point` that allows changing error messages based on the reason that will be given. This will also be useful for #51026, #51169 and maybe further changes to does not live long enough messages.

src/test/ui/span/borrowck-let-suggestion-suffixes.nll.stderr

@@ -8,6 +8,8 @@ LL |     v3.push(&id('x'));           // statement 6
 ...
 LL |     (v1, v2, v3, /* v4 is above. */ v5).use_ref();
    |              -- borrow later used here
+   |
+   = note: consider using a `let` binding to create a longer lived value
 
 error[E0597]: borrowed value does not live long enough
   --> $DIR/borrowck-let-suggestion-suffixes.rs:38:18
@@ -19,6 +21,8 @@ LL |         v4.push(&id('y'));
 ...
 LL |         v4.use_ref();
    |         -- borrow later used here
+   |
+   = note: consider using a `let` binding to create a longer lived value
 
 error[E0597]: borrowed value does not live long enough
   --> $DIR/borrowck-let-suggestion-suffixes.rs:49:14
@@ -30,6 +34,8 @@ LL |     v5.push(&id('z'));
 ...
 LL |     (v1, v2, v3, /* v4 is above. */ v5).use_ref();
    |                                     -- borrow later used here
+   |
+   = note: consider using a `let` binding to create a longer lived value
 
 error: aborting due to 3 previous errors
 

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

@@ -8,6 +8,8 @@ LL |     }
    |     - temporary value only lives until here
 LL |     println!("{}", *msg);
    |                    ---- borrow later used here
+   |
+   = note: consider using a `let` binding to create a longer lived value
 
 error: aborting due to previous error
 

src/test/ui/span/issue-15480.nll.stderr

@@ -8,6 +8,8 @@ LL |     ];
 ...
 LL |     for &&x in &v {
    |                -- borrow later used here
+   |
+   = note: consider using a `let` binding to create a longer lived value
 
 error: aborting due to previous error
 

src/test/ui/span/regions-close-over-borrowed-ref-in-obj.nll.stderr

@@ -8,6 +8,8 @@ LL |     }
    |     - temporary value only lives until here
 LL | }
    | - borrow later used here, when `blah` is dropped
+   |
+   = note: consider using a `let` binding to create a longer lived value
 
 error: aborting due to previous error
 

src/test/ui/span/slice-borrow.nll.stderr

@@ -9,6 +9,7 @@ LL |     }
 LL |     y.use_ref();
    |     - borrow later used here
    |
+   = note: consider using a `let` binding to create a longer lived value
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to previous error