Change to give a help message

Author: JohnGinger

src/librustc/middle/liveness.rs

@@ -1657,13 +1657,15 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
     fn report_dead_assign(&self, hir_id: HirId, sp: Span, var: Variable, is_argument: bool) {
         if let Some(name) = self.should_warn(var) {
             if is_argument {
-                self.ir.tcx.lint_hir(lint::builtin::UNUSED_ASSIGNMENTS, hir_id, sp,
-                    &format!("value passed to `{}` is never read
-                     (maybe it is overwritten before being read)", name));
+                self.ir.tcx.struct_span_lint_hir(lint::builtin::UNUSED_ASSIGNMENTS, hir_id, sp,
+                &format!("value passed to `{}` is never read", name))
+                .help("maybe it is overwritten before being read?")
+                .emit();
             } else {
-                self.ir.tcx.lint_hir(lint::builtin::UNUSED_ASSIGNMENTS, hir_id, sp,
-                    &format!("value assigned to `{}` is never read
-                     (maybe it is overwritten before being read)", name));
+                self.ir.tcx.struct_span_lint_hir(lint::builtin::UNUSED_ASSIGNMENTS, hir_id, sp,
+                &format!("value assigned to `{}` is never read", name))
+                .help("maybe it is overwritten before being read?")
+                .emit();
             }
         }
     }

src/test/ui/lint/issue-47390-unused-variable-in-struct-pattern.stderr

@@ -44,7 +44,6 @@ LL |                          mut hours_are_suns,
    = note: consider using `_hours_are_suns` instead
 
 warning: value assigned to `hours_are_suns` is never read
-                     (maybe it is overwritten before being read)
   --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:50:9
    |
 LL |         hours_are_suns = false;
@@ -56,6 +55,7 @@ note: lint level defined here
 LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
    |         ^^^^^^
    = note: #[warn(unused_assignments)] implied by #[warn(unused)]
+   = help: maybe it is overwritten before being read?
 
 warning: unused variable: `fire`
   --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:54:32

src/test/ui/liveness/liveness-dead.stderr

@@ -1,5 +1,4 @@
 error: value assigned to `x` is never read
-                     (maybe it is overwritten before being read)
   --> $DIR/liveness-dead.rs:19:13
    |
 LL |     let mut x: isize = 3; //~ ERROR: value assigned to `x` is never read
@@ -10,27 +9,31 @@ note: lint level defined here
    |
 LL | #![deny(unused_assignments)]
    |         ^^^^^^^^^^^^^^^^^^
+   = help: maybe it is overwritten before being read?
 
 error: value assigned to `x` is never read
-                     (maybe it is overwritten before being read)
   --> $DIR/liveness-dead.rs:27:5
    |
 LL |     x = 4; //~ ERROR: value assigned to `x` is never read
    |     ^
+   |
+   = help: maybe it is overwritten before being read?
 
 error: value passed to `x` is never read
-                     (maybe it is overwritten before being read)
   --> $DIR/liveness-dead.rs:30:11
    |
 LL | fn f4(mut x: i32) { //~ ERROR: value passed to `x` is never read
    |           ^
+   |
+   = help: maybe it is overwritten before being read?
 
 error: value assigned to `x` is never read
-                     (maybe it is overwritten before being read)
   --> $DIR/liveness-dead.rs:37:5
    |
 LL |     x = 4; //~ ERROR: value assigned to `x` is never read
    |     ^
+   |
+   = help: maybe it is overwritten before being read?
 
 error: aborting due to 4 previous errors
 

src/test/ui/liveness/liveness-unused.stderr

@@ -50,7 +50,6 @@ LL |     let mut x = 3;
    = note: consider using `_x` instead
 
 error: value assigned to `x` is never read
-                     (maybe it is overwritten before being read)
   --> $DIR/liveness-unused.rs:42:5
    |
 LL |     x += 4;
@@ -61,6 +60,7 @@ note: lint level defined here
    |
 LL | #![deny(unused_assignments)]
    |         ^^^^^^^^^^^^^^^^^^
+   = help: maybe it is overwritten before being read?
 
 error: variable `z` is assigned to, but never used
   --> $DIR/liveness-unused.rs:47:13
@@ -103,11 +103,12 @@ LL |     let x;
    = note: consider using `_x` instead
 
 error: value assigned to `x` is never read
-                     (maybe it is overwritten before being read)
   --> $DIR/liveness-unused.rs:126:9
    |
 LL |         x = 0;  //~ ERROR value assigned to `x` is never read
    |         ^
+   |
+   = help: maybe it is overwritten before being read?
 
 error: aborting due to 13 previous errors