Use smaller span for adjustments on block expressions

src/librustc_mir/hair/cx/expr.rs

@@ -78,7 +78,7 @@ fn apply_adjustment<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                                     mut expr: Expr<'tcx>,
                                     adjustment: &Adjustment<'tcx>)
                                     -> Expr<'tcx> {
-    let Expr { temp_lifetime, span, .. } = expr;
+    let Expr { temp_lifetime, mut span, .. } = expr;
     let kind = match adjustment.kind {
         Adjust::ReifyFnPointer => {
             ExprKind::ReifyFnPointer { source: expr.to_ref() }
@@ -96,6 +96,25 @@ fn apply_adjustment<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
             ExprKind::Cast { source: expr.to_ref() }
         }
         Adjust::Deref(None) => {
+            // Adjust the span from the block, to the last expression of the
+            // block. This is a better span when returning a mutable reference
+            // with too short a lifetime. The error message will use the span
+            // from the assignment to the return place, which should only point
+            // at the returned value, not the entire function body.
+            //
+            // fn return_short_lived<'a>(x: &'a mut i32) -> &'static mut i32 {
+            //      x
+            //   // ^ error message points at this expression.
+            // }
+            //
+            // We don't need to do this adjustment in the next match arm since
+            // deref coercions always start with a built-in deref.
+            if let ExprKind::Block { body } = expr.kind {
+                if let Some(ref last_expr) = body.expr {
+                    span = last_expr.span;
+                    expr.span = span;
+                }
+            }
             ExprKind::Deref { arg: expr.to_ref() }
         }
         Adjust::Deref(Some(deref)) => {

src/test/ui/issues/issue-17718-const-bad-values.rs

@@ -15,6 +15,5 @@ static mut S: usize = 3;
 const C2: &'static mut usize = unsafe { &mut S };
 //~^ ERROR: constants cannot refer to statics
 //~| ERROR: references in constants may only refer to immutable values
-//~| ERROR: references in constants may only refer to immutable values
 
 fn main() {}

src/test/ui/issues/issue-17718-const-bad-values.stderr

@@ -16,13 +16,7 @@ error[E0017]: references in constants may only refer to immutable values
 LL | const C2: &'static mut usize = unsafe { &mut S };
    |                                         ^^^^^^ constants require immutable values
 
-error[E0017]: references in constants may only refer to immutable values
+error: aborting due to 3 previous errors
-  --> $DIR/issue-17718-const-bad-values.rs:15:32
-   |
-LL | const C2: &'static mut usize = unsafe { &mut S };
-   |                                ^^^^^^^^^^^^^^^^^ constants require immutable values
-
-error: aborting due to 4 previous errors
 
 Some errors occurred: E0013, E0017.
 For more information about an error, try `rustc --explain E0013`.

src/test/ui/issues/issue-46471-1.stderr

@@ -12,16 +12,13 @@ LL | }
 error[E0597]: `z` does not live long enough (Mir)
   --> $DIR/issue-46471-1.rs:16:9
    |
-LL |       let y = {
+LL |         &mut z
-   |  _____________-
+   |         ^^^^^^
-LL | |         let mut z = 0;
+   |         |
-LL | |         &mut z
+   |         borrowed value does not live long enough
-   | |         ^^^^^^ borrowed value does not live long enough
+   |         borrow later used here
-LL | |     };
+LL |     };
-   | |     -
+   |     - `z` dropped here while still borrowed
-   | |     |
-   | |_____`z` dropped here while still borrowed
-   |       borrow later used here
 
 error: aborting due to 2 previous errors
 

src/test/ui/match/match-ref-mut-invariance.nll.stderr

@@ -5,17 +5,14 @@ LL |         match self.0 { ref mut x => x } //~ ERROR mismatched types
    |                                     ^
 
 error: unsatisfied lifetime constraints
-  --> $DIR/match-ref-mut-invariance.rs:19:49
+  --> $DIR/match-ref-mut-invariance.rs:20:9
    |
-LL |   impl<'b> S<'b> {
+LL | impl<'b> S<'b> {
-   |        -- lifetime `'b` defined here
+   |      -- lifetime `'b` defined here
-LL |       fn bar<'a>(&'a mut self) -> &'a mut &'a i32 {
+LL |     fn bar<'a>(&'a mut self) -> &'a mut &'a i32 {
-   |  ____________--___________________________________^
+   |            -- lifetime `'a` defined here
-   | |            |
+LL |         match self.0 { ref mut x => x } //~ ERROR mismatched types
-   | |            lifetime `'a` defined here
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'b`
-LL | |         match self.0 { ref mut x => x } //~ ERROR mismatched types
-LL | |     }
-   | |_____^ returning this value requires that `'a` must outlive `'b`
 
 error: aborting due to previous error
 

src/test/ui/match/match-ref-mut-let-invariance.nll.stderr

@@ -5,18 +5,15 @@ LL |         x //~ ERROR mismatched types
    |         ^
 
 error: unsatisfied lifetime constraints
-  --> $DIR/match-ref-mut-let-invariance.rs:19:49
+  --> $DIR/match-ref-mut-let-invariance.rs:21:9
    |
-LL |   impl<'b> S<'b> {
+LL | impl<'b> S<'b> {
-   |        -- lifetime `'b` defined here
+   |      -- lifetime `'b` defined here
-LL |       fn bar<'a>(&'a mut self) -> &'a mut &'a i32 {
+LL |     fn bar<'a>(&'a mut self) -> &'a mut &'a i32 {
-   |  ____________--___________________________________^
+   |            -- lifetime `'a` defined here
-   | |            |
+LL |         let ref mut x = self.0;
-   | |            lifetime `'a` defined here
+LL |         x //~ ERROR mismatched types
-LL | |         let ref mut x = self.0;
+   |         ^ returning this value requires that `'a` must outlive `'b`
-LL | |         x //~ ERROR mismatched types
-LL | |     }
-   | |_____^ returning this value requires that `'a` must outlive `'b`
 
 error: aborting due to previous error
 

src/test/ui/nll/mir_check_cast_unsize.rs

@@ -15,9 +15,9 @@
 use std::fmt::Debug;
 
 fn bar<'a>(x: &'a u32) -> &'static dyn Debug {
-    //~^ ERROR unsatisfied lifetime constraints
     x
-    //~^ WARNING not reporting region error due to nll
+    //~^ ERROR unsatisfied lifetime constraints
+    //~| WARNING not reporting region error due to nll
 }
 
 fn main() {}

src/test/ui/nll/mir_check_cast_unsize.stderr

@@ -1,21 +1,16 @@
 warning: not reporting region error due to nll
-  --> $DIR/mir_check_cast_unsize.rs:19:5
+  --> $DIR/mir_check_cast_unsize.rs:18:5
    |
 LL |     x
    |     ^
 
 error: unsatisfied lifetime constraints
-  --> $DIR/mir_check_cast_unsize.rs:17:46
+  --> $DIR/mir_check_cast_unsize.rs:18:5
    |
-LL |   fn bar<'a>(x: &'a u32) -> &'static dyn Debug {
+LL | fn bar<'a>(x: &'a u32) -> &'static dyn Debug {
-   |  ________--____________________________________^
+   |        -- lifetime `'a` defined here
-   | |        |
+LL |     x
-   | |        lifetime `'a` defined here
+   |     ^ returning this value requires that `'a` must outlive `'static`
-LL | |     //~^ ERROR unsatisfied lifetime constraints
-LL | |     x
-LL | |     //~^ WARNING not reporting region error due to nll
-LL | | }
-   | |_^ returning this value requires that `'a` must outlive `'static`
 
 error: aborting due to previous error
 

src/test/ui/object-lifetime/object-lifetime-default-elision.nll.stderr

@@ -5,20 +5,15 @@ LL |     ss
    |     ^^
 
 error: unsatisfied lifetime constraints
-  --> $DIR/object-lifetime-default-elision.rs:64:53
+  --> $DIR/object-lifetime-default-elision.rs:81:5
    |
-LL |   fn load3<'a,'b>(ss: &'a SomeTrait) -> &'b SomeTrait {
+LL | fn load3<'a,'b>(ss: &'a SomeTrait) -> &'b SomeTrait {
-   |  __________--_--______________________________________^
+   |          -- -- lifetime `'b` defined here
-   | |          |  |
+   |          |
-   | |          |  lifetime `'b` defined here
+   |          lifetime `'a` defined here
-   | |          lifetime `'a` defined here
+...
-LL | |     // Under old rules, the fully elaborated types of input/output were:
+LL |     ss
-LL | |     //
+   |     ^^ returning this value requires that `'a` must outlive `'b`
-LL | |     // for<'a,'b,'c>fn(&'a (SomeTrait+'c)) -> &'b (SomeTrait+'a)
-...  |
-LL | |         //~| ERROR cannot infer
-LL | | }
-   | |_^ returning this value requires that `'a` must outlive `'b`
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-reborrow-from-shorter-mut-ref-mut-ref.nll.stderr

@@ -5,16 +5,14 @@ LL |     &mut ***p //~ ERROR 14:5: 14:14: lifetime mismatch [E0623]
    |     ^^^^^^^^^
 
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-reborrow-from-shorter-mut-ref-mut-ref.rs:13:85
+  --> $DIR/regions-reborrow-from-shorter-mut-ref-mut-ref.rs:14:5
    |
-LL |   fn copy_borrowed_ptr<'a, 'b, 'c>(p: &'a mut &'b mut &'c mut isize) -> &'b mut isize {
+LL | fn copy_borrowed_ptr<'a, 'b, 'c>(p: &'a mut &'b mut &'c mut isize) -> &'b mut isize {
-   |  ______________________--__--_________________________________________________________^
+   |                      --  -- lifetime `'b` defined here
-   | |                      |   |
+   |                      |
-   | |                      |   lifetime `'b` defined here
+   |                      lifetime `'a` defined here
-   | |                      lifetime `'a` defined here
+LL |     &mut ***p //~ ERROR 14:5: 14:14: lifetime mismatch [E0623]
-LL | |     &mut ***p //~ ERROR 14:5: 14:14: lifetime mismatch [E0623]
+   |     ^^^^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
-LL | | }
-   | |_^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-reborrow-from-shorter-mut-ref.nll.stderr

@@ -5,16 +5,14 @@ LL |     &mut **p //~ ERROR 16:5: 16:13: lifetime mismatch [E0623]
    |     ^^^^^^^^
 
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-reborrow-from-shorter-mut-ref.rs:15:73
+  --> $DIR/regions-reborrow-from-shorter-mut-ref.rs:16:5
    |
-LL |   fn copy_borrowed_ptr<'a, 'b>(p: &'a mut &'b mut isize) -> &'b mut isize {
+LL | fn copy_borrowed_ptr<'a, 'b>(p: &'a mut &'b mut isize) -> &'b mut isize {
-   |  ______________________--__--_____________________________________________^
+   |                      --  -- lifetime `'b` defined here
-   | |                      |   |
+   |                      |
-   | |                      |   lifetime `'b` defined here
+   |                      lifetime `'a` defined here
-   | |                      lifetime `'a` defined here
+LL |     &mut **p //~ ERROR 16:5: 16:13: lifetime mismatch [E0623]
-LL | |     &mut **p //~ ERROR 16:5: 16:13: lifetime mismatch [E0623]
+   |     ^^^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
-LL | | }
-   | |_^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-trait-object-subtyping.nll.stderr

@@ -11,18 +11,15 @@ LL |     x //~ ERROR mismatched types
    |     ^
 
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-trait-object-subtyping.rs:23:51
+  --> $DIR/regions-trait-object-subtyping.rs:25:5
    |
-LL |   fn foo3<'a,'b>(x: &'a mut Dummy) -> &'b mut Dummy {
+LL | fn foo3<'a,'b>(x: &'a mut Dummy) -> &'b mut Dummy {
-   |  _________--_--_____________________________________^
+   |         -- -- lifetime `'b` defined here
-   | |         |  |
+   |         |
-   | |         |  lifetime `'b` defined here
+   |         lifetime `'a` defined here
-   | |         lifetime `'a` defined here
+LL |     // Without knowing 'a:'b, we can't coerce
-LL | |     // Without knowing 'a:'b, we can't coerce
+LL |     x //~ ERROR lifetime bound not satisfied
-LL | |     x //~ ERROR lifetime bound not satisfied
+   |     ^ returning this value requires that `'a` must outlive `'b`
-LL | |      //~^ ERROR cannot infer an appropriate lifetime
-LL | | }
-   | |_^ returning this value requires that `'a` must outlive `'b`
 
 error: unsatisfied lifetime constraints
   --> $DIR/regions-trait-object-subtyping.rs:32:5