Auto merge of rust-lang#86426 - hi-rustin:rustin-patch-lint-warn, r=Aaron1011

Lint for unused borrows as part of UNUSED_MUST_USE

close rust-lang#76264

base on rust-lang#76894

r? `@RalfJung`

Author: bors

compiler/rustc_lint/src/unused.rs

@@ -154,6 +154,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                 | hir::BinOpKind::Shl
                 | hir::BinOpKind::Shr => Some("bitwise operation"),
             },
+            hir::ExprKind::AddrOf(..) => Some("borrow"),
             hir::ExprKind::Unary(..) => Some("unary operation"),
             _ => None,
         };

compiler/rustc_macros/src/hash_stable.rs

@@ -54,7 +54,7 @@ pub fn hash_stable_generic_derive(mut s: synstructure::Structure<'_>) -> proc_ma
             quote! {}
         } else if let Some(project) = attrs.project {
             quote! {
-                &#bi.#project.hash_stable(__hcx, __hasher);
+                (&#bi.#project).hash_stable(__hcx, __hasher);
             }
         } else {
             quote! {
@@ -96,7 +96,7 @@ pub fn hash_stable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::To
             quote! {}
         } else if let Some(project) = attrs.project {
             quote! {
-                &#bi.#project.hash_stable(__hcx, __hasher);
+                (&#bi.#project).hash_stable(__hcx, __hasher);
             }
         } else {
             quote! {

library/alloc/tests/str.rs

@@ -534,7 +534,7 @@ mod slice_index {
     #[test]
     #[should_panic]
     fn test_slice_fail() {
-        &"中华Việt Nam"[0..2];
+        let _ = &"中华Việt Nam"[0..2];
     }
 
     panic_cases! {
@@ -714,13 +714,13 @@ mod slice_index {
     #[test]
     #[should_panic(expected = "byte index 1024 is out of bounds of `Lorem ipsum dolor sit amet")]
     fn test_slice_fail_truncated_1() {
-        &LOREM_PARAGRAPH[..1024];
+        let _ = &LOREM_PARAGRAPH[..1024];
     }
     // check the truncation in the panic message
     #[test]
     #[should_panic(expected = "luctus, im`[...]")]
     fn test_slice_fail_truncated_2() {
-        &LOREM_PARAGRAPH[..1024];
+        let _ = &LOREM_PARAGRAPH[..1024];
     }
 }
 
@@ -735,7 +735,7 @@ fn test_str_slice_rangetoinclusive_ok() {
 #[should_panic]
 fn test_str_slice_rangetoinclusive_notok() {
     let s = "abcαβγ";
-    &s[..=3];
+    let _ = &s[..=3];
 }
 
 #[test]
@@ -751,7 +751,7 @@ fn test_str_slicemut_rangetoinclusive_ok() {
 fn test_str_slicemut_rangetoinclusive_notok() {
     let mut s = "abcαβγ".to_owned();
     let s: &mut str = &mut s;
-    &mut s[..=3];
+    let _ = &mut s[..=3];
 }
 
 #[test]

library/alloc/tests/vec.rs

@@ -542,35 +542,35 @@ fn test_index_out_of_bounds() {
 #[should_panic]
 fn test_slice_out_of_bounds_1() {
     let x = vec![1, 2, 3, 4, 5];
-    &x[!0..];
+    let _ = &x[!0..];
 }
 
 #[test]
 #[should_panic]
 fn test_slice_out_of_bounds_2() {
     let x = vec![1, 2, 3, 4, 5];
-    &x[..6];
+    let _ = &x[..6];
 }
 
 #[test]
 #[should_panic]
 fn test_slice_out_of_bounds_3() {
     let x = vec![1, 2, 3, 4, 5];
-    &x[!0..4];
+    let _ = &x[!0..4];
 }
 
 #[test]
 #[should_panic]
 fn test_slice_out_of_bounds_4() {
     let x = vec![1, 2, 3, 4, 5];
-    &x[1..6];
+    let _ = &x[1..6];
 }
 
 #[test]
 #[should_panic]
 fn test_slice_out_of_bounds_5() {
     let x = vec![1, 2, 3, 4, 5];
-    &x[3..2];
+    let _ = &x[3..2];
 }
 
 #[test]

library/std/src/sys_common/wtf8/tests.rs

@@ -301,7 +301,7 @@ fn wtf8_slice() {
 #[test]
 #[should_panic]
 fn wtf8_slice_not_code_point_boundary() {
-    &Wtf8::from_str("aé 💩")[2..4];
+    let _ = &Wtf8::from_str("aé 💩")[2..4];
 }
 
 #[test]
@@ -312,7 +312,7 @@ fn wtf8_slice_from() {
 #[test]
 #[should_panic]
 fn wtf8_slice_from_not_code_point_boundary() {
-    &Wtf8::from_str("aé 💩")[2..];
+    let _ = &Wtf8::from_str("aé 💩")[2..];
 }
 
 #[test]
@@ -323,7 +323,7 @@ fn wtf8_slice_to() {
 #[test]
 #[should_panic]
 fn wtf8_slice_to_not_code_point_boundary() {
-    &Wtf8::from_str("aé 💩")[5..];
+    let _ = &Wtf8::from_str("aé 💩")[5..];
 }
 
 #[test]

src/test/ui/array-slice-vec/slice-panic-1.rs

@@ -17,7 +17,7 @@ impl Drop for Foo {
 
 fn foo() {
     let x: &[_] = &[Foo, Foo];
-    &x[3..4];
+    let _ = &x[3..4];
 }
 
 fn main() {

src/test/ui/array-slice-vec/slice-panic-2.rs

@@ -21,7 +21,7 @@ fn bar() -> usize {
 
 fn foo() {
     let x: &[_] = &[Foo, Foo];
-    &x[3..bar()];
+    let _ = &x[3..bar()];
 }
 
 fn main() {

src/test/ui/array-slice-vec/slice.rs

@@ -67,14 +67,14 @@ impl IndexMut<RangeFull> for Foo {
 
 fn main() {
     let mut x = Foo;
-    &x[..];
-    &x[Foo..];
-    &x[..Foo];
-    &x[Foo..Foo];
-    &mut x[..];
-    &mut x[Foo..];
-    &mut x[..Foo];
-    &mut x[Foo..Foo];
+    let _ = &x[..];
+    let _ = &x[Foo..];
+    let _ = &x[..Foo];
+    let _ = &x[Foo..Foo];
+    let _ = &mut x[..];
+    let _ = &mut x[Foo..];
+    let _ = &mut x[..Foo];
+    let _ = &mut x[Foo..Foo];
     unsafe {
         assert_eq!(COUNT, 8);
     }

src/test/ui/const-generics/issues/issue-61432.rs

@@ -6,9 +6,9 @@ fn promote<const N: i32>() {
     // works:
     //
     // let n = N;
-    // &n;
+    // let _ = &n;
 
-    &N;
+    let _ = &N;
 }
 
 fn main() {

src/test/ui/dynamically-sized-types/dst-index.rs

@@ -29,6 +29,6 @@ impl Index<usize> for T {
 
 fn main() {
     assert_eq!(&S[0], "hello");
-    &T[0];
+    let _ = &T[0];
     // let x = &x as &Debug;
 }