Enable rustfix on `unused_unit` tests

tests/ui/unused_unit.fixed

@@ -0,0 +1,44 @@
+// run-rustfix
+
+// The output for humans should just highlight the whole span without showing
+// the suggested replacement, but we also want to test that suggested
+// replacement only removes one set of parentheses, rather than naïvely
+// stripping away any starting or ending parenthesis characters—hence this
+// test of the JSON error format.
+
+#![feature(custom_inner_attributes)]
+#![rustfmt::skip]
+
+#![deny(clippy::unused_unit)]
+
+struct Unitter;
+impl Unitter {
+    // try to disorient the lint with multiple unit returns and newlines
+    #[allow(clippy::no_effect)]
+    pub fn get_unit<F: Fn() -> (), G>(&self, f: F, _g: G) 
+    where G: Fn() -> () {
+        let _y: &Fn() -> () = &f;
+        (); // this should not lint, as it's not in return type position
+    }
+}
+
+impl Into<()> for Unitter {
+    #[rustfmt::skip]
+    fn into(self)  {
+        
+    }
+}
+
+fn return_unit()  {  }
+
+#[allow(clippy::needless_return)]
+#[allow(clippy::never_loop)]
+fn main() {
+    let u = Unitter;
+    assert_eq!(u.get_unit(|| {}, return_unit), u.into());
+    return_unit();
+    loop {
+        break;
+    }
+    return;
+}

tests/ui/unused_unit.rs

@@ -1,4 +1,4 @@
-// compile-pass
+// run-rustfix
 
 // The output for humans should just highlight the whole span without showing
 // the suggested replacement, but we also want to test that suggested
@@ -6,14 +6,15 @@
 // stripping away any starting or ending parenthesis characters—hence this
 // test of the JSON error format.
 
-#![deny(clippy::unused_unit)]
-#![allow(clippy::needless_return)]
 #![feature(custom_inner_attributes)]
 #![rustfmt::skip]
 
+#![deny(clippy::unused_unit)]
+
 struct Unitter;
 impl Unitter {
     // try to disorient the lint with multiple unit returns and newlines
+    #[allow(clippy::no_effect)]
     pub fn get_unit<F: Fn() -> (), G>(&self, f: F, _g: G) ->
         ()
     where G: Fn() -> () {
@@ -31,6 +32,8 @@ impl Into<()> for Unitter {
 
 fn return_unit() -> () { () }
 
+#[allow(clippy::needless_return)]
+#[allow(clippy::never_loop)]
 fn main() {
     let u = Unitter;
     assert_eq!(u.get_unit(|| {}, return_unit), u.into());

tests/ui/unused_unit.stderr

@@ -1,5 +1,5 @@
 error: unneeded unit return type
-  --> $DIR/unused_unit.rs:17:59
+  --> $DIR/unused_unit.rs:18:59
    |
 LL |       pub fn get_unit<F: Fn() -> (), G>(&self, f: F, _g: G) ->
    |  ___________________________________________________________^
@@ -7,43 +7,43 @@ LL | |         ()
    | |__________^ help: remove the `-> ()`
    |
 note: lint level defined here
-  --> $DIR/unused_unit.rs:9:9
+  --> $DIR/unused_unit.rs:12:9
    |
 LL | #![deny(clippy::unused_unit)]
    |         ^^^^^^^^^^^^^^^^^^^
 
 error: unneeded unit return type
-  --> $DIR/unused_unit.rs:27:19
+  --> $DIR/unused_unit.rs:28:19
    |
 LL |     fn into(self) -> () {
    |                   ^^^^^ help: remove the `-> ()`
 
 error: unneeded unit expression
-  --> $DIR/unused_unit.rs:28:9
+  --> $DIR/unused_unit.rs:29:9
    |
 LL |         ()
    |         ^^ help: remove the final `()`
 
 error: unneeded unit return type
-  --> $DIR/unused_unit.rs:32:18
+  --> $DIR/unused_unit.rs:33:18
    |
 LL | fn return_unit() -> () { () }
    |                  ^^^^^ help: remove the `-> ()`
 
 error: unneeded unit expression
-  --> $DIR/unused_unit.rs:32:26
+  --> $DIR/unused_unit.rs:33:26
    |
 LL | fn return_unit() -> () { () }
    |                          ^^ help: remove the final `()`
 
 error: unneeded `()`
-  --> $DIR/unused_unit.rs:39:14
+  --> $DIR/unused_unit.rs:42:14
    |
 LL |         break();
    |              ^^ help: remove the `()`
 
 error: unneeded `()`
-  --> $DIR/unused_unit.rs:41:11
+  --> $DIR/unused_unit.rs:44:11
    |
 LL |     return();
    |           ^^ help: remove the `()`