Correct unused field warning on &struct match

Author: varkor

src/librustc/middle/liveness.rs

@@ -412,18 +412,28 @@ fn visit_local<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, local: &'tcx hir::Local) {
 }
 
 fn visit_arm<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, arm: &'tcx hir::Arm) {
-    for pat in &arm.pats {
-        // for struct patterns, take note of which fields used shorthand (`x` rather than `x: x`)
+    for mut pat in &arm.pats {
+        // For struct patterns, take note of which fields used shorthand
+        // (`x` rather than `x: x`).
         //
-        // FIXME: according to the rust-lang-nursery/rustc-guide book, `NodeId`s are to be phased
-        // out in favor of `HirId`s; however, we need to match the signature of `each_binding`,
-        // which uses `NodeIds`.
+        // FIXME: according to the rust-lang-nursery/rustc-guide book, `NodeId`s are to be
+        // phased out in favor of `HirId`s; however, we need to match the signature of
+        // `each_binding`, which uses `NodeIds`.
         let mut shorthand_field_ids = NodeSet();
-        if let hir::PatKind::Struct(_, ref fields, _) = pat.node {
-            for field in fields {
-                if field.node.is_shorthand {
-                    shorthand_field_ids.insert(field.node.pat.id);
+        loop {
+            match pat.node {
+                hir::PatKind::Struct(_, ref fields, _) => {
+                    for field in fields {
+                        if field.node.is_shorthand {
+                            shorthand_field_ids.insert(field.node.pat.id);
+                        }
+                    }
+                    break;
+                }
+                hir::PatKind::Ref(ref deref_pat, _) => {
+                    pat = deref_pat;
                 }
+                _ => break
             }
         }
 

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

@@ -18,6 +18,10 @@ struct SoulHistory {
     endless_and_singing: bool
 }
 
+enum Large {
+    Suit { case: () }
+}
+
 fn main() {
     let i_think_continually = 2;
     let who_from_the_womb_remembered = SoulHistory {
@@ -31,4 +35,12 @@ fn main() {
                          endless_and_singing: true } = who_from_the_womb_remembered {
         hours_are_suns = false;
     }
+
+    let bag = &Large::Suit {
+        case: ()
+    };
+
+    match bag {
+        &Large::Suit { case } => {}
+    };
 }

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

@@ -1,5 +1,5 @@
 warning: unused variable: `i_think_continually`
-  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:22:9
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:26:9
    |
 LL |     let i_think_continually = 2;
    |         ^^^^^^^^^^^^^^^^^^^ help: consider using `_i_think_continually` instead
@@ -12,21 +12,21 @@ 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:29:26
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:33:26
    |
 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:30:26
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:34:26
    |
 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:32:9
+  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:36:9
    |
 LL |         hours_are_suns = false;
    |         ^^^^^^^^^^^^^^
@@ -38,3 +38,9 @@ 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
+   |
+LL |         &Large::Suit { case } => {}
+   |                        ^^^^ help: try ignoring the field: `case: _`
+