Rollup merge of rust-lang#66469 - CosineP:fix/field-lint, r=petrochenkov

Use "field is never read" instead of "field is never used"

this is my first PR here so please let me know if i am doing it wrong
closes rust-lang#64465
i will be referencing this with a book PR that updates the same language

Author: JohnTitor

src/librustc_passes/dead.rs

@@ -631,7 +631,7 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
 
     fn visit_struct_field(&mut self, field: &'tcx hir::StructField) {
         if self.should_warn_about_field(&field) {
-            self.warn_dead_code(field.hir_id, field.span, field.ident.name, "field", "used");
+            self.warn_dead_code(field.hir_id, field.span, field.ident.name, "field", "read");
         }
         intravisit::walk_struct_field(self, field);
     }

src/test/ui/lint/dead-code/lint-dead-code-4.rs

@@ -4,7 +4,7 @@
 
 struct Foo {
     x: usize,
-    b: bool, //~ ERROR: field is never used
+    b: bool, //~ ERROR: field is never read
 }
 
 fn field_read(f: Foo) -> usize {
@@ -36,8 +36,8 @@ enum IJK {
     I, //~ ERROR variant is never constructed
     J {
         a: String,
-        b: i32, //~ ERROR field is never used
-        c: i32, //~ ERROR field is never used
+        b: i32, //~ ERROR field is never read
+        c: i32, //~ ERROR field is never read
     },
     K //~ ERROR variant is never constructed
 
@@ -58,9 +58,9 @@ fn field_match_in_patterns(b: XYZ) -> String {
 }
 
 struct Bar {
-    x: usize, //~ ERROR: field is never used
+    x: usize, //~ ERROR: field is never read
     b: bool,
-    c: bool, //~ ERROR: field is never used
+    c: bool, //~ ERROR: field is never read
     _guard: ()
 }
 

src/test/ui/lint/dead-code/lint-dead-code-4.stderr

@@ -1,4 +1,4 @@
-error: field is never used: `b`
+error: field is never read: `b`
   --> $DIR/lint-dead-code-4.rs:7:5
    |
 LL |     b: bool,
@@ -38,13 +38,13 @@ error: variant is never constructed: `I`
 LL |     I,
    |     ^
 
-error: field is never used: `b`
+error: field is never read: `b`
   --> $DIR/lint-dead-code-4.rs:39:9
    |
 LL |         b: i32,
    |         ^^^^^^
 
-error: field is never used: `c`
+error: field is never read: `c`
   --> $DIR/lint-dead-code-4.rs:40:9
    |
 LL |         c: i32,
@@ -56,13 +56,13 @@ error: variant is never constructed: `K`
 LL |     K
    |     ^
 
-error: field is never used: `x`
+error: field is never read: `x`
   --> $DIR/lint-dead-code-4.rs:61:5
    |
 LL |     x: usize,
    |     ^^^^^^^^
 
-error: field is never used: `c`
+error: field is never read: `c`
   --> $DIR/lint-dead-code-4.rs:63:5
    |
 LL |     c: bool,

src/test/ui/union/union-fields-1.rs

@@ -3,19 +3,19 @@
 union U1 {
     a: u8, // should not be reported
     b: u8, // should not be reported
-    c: u8, //~ ERROR field is never used
+    c: u8, //~ ERROR field is never read
 }
 union U2 {
-    a: u8, //~ ERROR field is never used
+    a: u8, //~ ERROR field is never read
     b: u8, // should not be reported
     c: u8, // should not be reported
 }
-union NoDropLike { a: u8 } //~ ERROR field is never used
+union NoDropLike { a: u8 } //~ ERROR field is never read
 
 union U {
     a: u8, // should not be reported
     b: u8, // should not be reported
-    c: u8, //~ ERROR field is never used
+    c: u8, //~ ERROR field is never read
 }
 type A = U;
 

src/test/ui/union/union-fields-1.stderr

@@ -1,4 +1,4 @@
-error: field is never used: `c`
+error: field is never read: `c`
   --> $DIR/union-fields-1.rs:6:5
    |
 LL |     c: u8,
@@ -10,19 +10,19 @@ note: lint level defined here
 LL | #![deny(dead_code)]
    |         ^^^^^^^^^
 
-error: field is never used: `a`
+error: field is never read: `a`
   --> $DIR/union-fields-1.rs:9:5
    |
 LL |     a: u8,
    |     ^^^^^
 
-error: field is never used: `a`
+error: field is never read: `a`
   --> $DIR/union-fields-1.rs:13:20
    |
 LL | union NoDropLike { a: u8 }
    |                    ^^^^^
 
-error: field is never used: `c`
+error: field is never read: `c`
   --> $DIR/union-fields-1.rs:18:5
    |
 LL |     c: u8,

src/test/ui/union/union-lint-dead-code.rs

@@ -2,7 +2,7 @@
 
 union Foo {
     x: usize,
-    b: bool, //~ ERROR: field is never used
+    b: bool, //~ ERROR: field is never read
     _unused: u16,
 }
 

src/test/ui/union/union-lint-dead-code.stderr

@@ -1,4 +1,4 @@
-error: field is never used: `b`
+error: field is never read: `b`
   --> $DIR/union-lint-dead-code.rs:5:5
    |
 LL |     b: bool,