add #[must_use] to functions of slice and its iterators.

Author: jendrikw

src/tools/clippy/tests/ui/bytes_nth.stderr

@@ -1,8 +1,8 @@
 error: called `.byte().nth()` on a `String`
-  --> $DIR/bytes_nth.rs:8:5
+  --> $DIR/bytes_nth.rs:8:13
    |
-LL |     s.bytes().nth(3);
-   |     ^^^^^^^^^^^^^^^^ help: try: `s.as_bytes().get(3)`
+LL |     let _ = s.bytes().nth(3);
+   |             ^^^^^^^^^^^^^^^^ help: try: `s.as_bytes().get(3)`
    |
    = note: `-D clippy::bytes-nth` implied by `-D warnings`
 
@@ -13,10 +13,10 @@ LL |     let _ = &s.bytes().nth(3);
    |              ^^^^^^^^^^^^^^^^ help: try: `s.as_bytes().get(3)`
 
 error: called `.byte().nth()` on a `str`
-  --> $DIR/bytes_nth.rs:10:5
+  --> $DIR/bytes_nth.rs:10:13
    |
-LL |     s[..].bytes().nth(3);
-   |     ^^^^^^^^^^^^^^^^^^^^ help: try: `s[..].as_bytes().get(3)`
+LL |     let _ = s[..].bytes().nth(3);
+   |             ^^^^^^^^^^^^^^^^^^^^ help: try: `s[..].as_bytes().get(3)`
 
 error: aborting due to 3 previous errors
 

src/tools/clippy/tests/ui/iter_next_slice.stderr

@@ -1,28 +1,28 @@
 error: using `.iter().next()` on an array
-  --> $DIR/iter_next_slice.rs:9:5
+  --> $DIR/iter_next_slice.rs:9:13
    |
-LL |     s.iter().next();
-   |     ^^^^^^^^^^^^^^^ help: try calling: `s.get(0)`
+LL |     let _ = s.iter().next();
+   |             ^^^^^^^^^^^^^^^ help: try calling: `s.get(0)`
    |
    = note: `-D clippy::iter-next-slice` implied by `-D warnings`
 
 error: using `.iter().next()` on a Slice without end index
-  --> $DIR/iter_next_slice.rs:12:5
+  --> $DIR/iter_next_slice.rs:12:13
    |
-LL |     s[2..].iter().next();
-   |     ^^^^^^^^^^^^^^^^^^^^ help: try calling: `s.get(2)`
+LL |     let _ = s[2..].iter().next();
+   |             ^^^^^^^^^^^^^^^^^^^^ help: try calling: `s.get(2)`
 
 error: using `.iter().next()` on a Slice without end index
-  --> $DIR/iter_next_slice.rs:15:5
+  --> $DIR/iter_next_slice.rs:15:13
    |
-LL |     v[5..].iter().next();
-   |     ^^^^^^^^^^^^^^^^^^^^ help: try calling: `v.get(5)`
+LL |     let _ = v[5..].iter().next();
+   |             ^^^^^^^^^^^^^^^^^^^^ help: try calling: `v.get(5)`
 
 error: using `.iter().next()` on an array
-  --> $DIR/iter_next_slice.rs:18:5
+  --> $DIR/iter_next_slice.rs:18:13
    |
-LL |     v.iter().next();
-   |     ^^^^^^^^^^^^^^^ help: try calling: `v.get(0)`
+LL |     let _ = v.iter().next();
+   |             ^^^^^^^^^^^^^^^ help: try calling: `v.get(0)`
 
 error: aborting due to 4 previous errors