Correct unused field warning on box struct match

Author: varkor

src/librustc/middle/liveness.rs

@@ -430,8 +430,9 @@ fn visit_arm<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, arm: &'tcx hir::Arm) {
                     }
                     break;
                 }
-                hir::PatKind::Ref(ref deref_pat, _) => {
-                    pat = deref_pat;
+                hir::PatKind::Ref(ref inner_pat, _) |
+                hir::PatKind::Box(ref inner_pat) => {
+                    pat = inner_pat;
                 }
                 _ => break
             }

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

@@ -10,6 +10,8 @@
 
 // compile-pass
 
+#![feature(box_syntax)]
+#![feature(box_patterns)]
 #![warn(unused)] // UI tests pass `-A unused` (#43896)
 
 struct SoulHistory {
@@ -36,11 +38,15 @@ fn main() {
         hours_are_suns = false;
     }
 
-    let bag = &Large::Suit {
+    let bag = Large::Suit {
         case: ()
     };
 
-    match bag {
+    match &bag {
         &Large::Suit { case } => {}
     };
+
+    match box bag {
+        box Large::Suit { case } => {}
+    };
 }

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

@@ -1,46 +1,52 @@
 warning: unused variable: `i_think_continually`
-  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:26:9
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:28:9
    |
 LL |     let i_think_continually = 2;
    |         ^^^^^^^^^^^^^^^^^^^ help: consider using `_i_think_continually` instead
    |
 note: lint level defined here
-  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:13:9
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:15:9
    |
 LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
    |         ^^^^^^
    = note: #[warn(unused_variables)] implied by #[warn(unused)]
 
 warning: unused variable: `corridors_of_light`
-  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:33:26
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:35:26
    |
 LL |     if let SoulHistory { corridors_of_light,
    |                          ^^^^^^^^^^^^^^^^^^ help: try ignoring the field: `corridors_of_light: _`
 
 warning: variable `hours_are_suns` is assigned to, but never used
-  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:34:26
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:36:26
    |
 LL |                          mut hours_are_suns,
    |                          ^^^^^^^^^^^^^^^^^^
    |
    = note: consider using `_hours_are_suns` instead
 
 warning: value assigned to `hours_are_suns` is never read
-  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:36:9
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:38:9
    |
 LL |         hours_are_suns = false;
    |         ^^^^^^^^^^^^^^
    |
 note: lint level defined here
-  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:13:9
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:15:9
    |
 LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
    |         ^^^^^^
    = note: #[warn(unused_assignments)] implied by #[warn(unused)]
 
 warning: unused variable: `case`
-  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:44:24
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:46:24
    |
 LL |         &Large::Suit { case } => {}
    |                        ^^^^ help: try ignoring the field: `case: _`
 
+warning: unused variable: `case`
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:50:27
+   |
+LL |         box Large::Suit { case } => {}
+   |                           ^^^^ help: try ignoring the field: `case: _`
+