Use libtest errors check to better enforce UI testing

tests/ui/needless_pass_by_ref_mut.rs

@@ -3,8 +3,8 @@
 
 use std::ptr::NonNull;
 
-// Should only warn for `s`.
 fn foo(s: &mut Vec<u32>, b: &u32, x: &mut u32) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
     *x += *b + s.len() as u32;
 }
 
@@ -28,8 +28,8 @@ fn foo5(s: &mut Vec<u32>) {
     foo2(s);
 }
 
-// Should warn.
 fn foo6(s: &mut Vec<u32>) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
     non_mut_ref(s);
 }
 
@@ -41,13 +41,13 @@ impl Bar {
     // Should not warn on `&mut self`.
     fn bar(&mut self) {}
 
-    // Should warn about `vec`
     fn mushroom(&self, vec: &mut Vec<i32>) -> usize {
+        //~^ ERROR: this argument is a mutable reference, but not used mutably
         vec.len()
     }
 
-    // Should warn about `vec` (and not `self`).
     fn badger(&mut self, vec: &mut Vec<i32>) -> usize {
+        //~^ ERROR: this argument is a mutable reference, but not used mutably
         vec.len()
     }
 }
@@ -123,36 +123,36 @@ async fn f7(x: &mut i32, y: i32, z: &mut i32, a: i32) {
     *z += 1;
 }
 
-// Should warn.
 async fn a1(x: &mut i32) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
     println!("{:?}", x);
 }
-// Should warn.
 async fn a2(x: &mut i32, y: String) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
     println!("{:?}", x);
 }
-// Should warn.
 async fn a3(x: &mut i32, y: String, z: String) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
     println!("{:?}", x);
 }
-// Should warn.
 async fn a4(x: &mut i32, y: i32) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
     println!("{:?}", x);
 }
-// Should warn.
 async fn a5(x: i32, y: &mut i32) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
     println!("{:?}", x);
 }
-// Should warn.
 async fn a6(x: i32, y: &mut i32) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
     println!("{:?}", x);
 }
-// Should warn.
 async fn a7(x: i32, y: i32, z: &mut i32) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
     println!("{:?}", z);
 }
-// Should warn.
 async fn a8(x: i32, a: &mut i32, y: i32, z: &mut i32) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
     println!("{:?}", z);
 }
 
@@ -185,13 +185,15 @@ fn used_as_path(s: &mut u32) {}
 fn lint_attr(s: &mut u32) {}
 
 #[cfg(not(feature = "a"))]
-// Should warn with note.
 fn cfg_warn(s: &mut u32) {}
+//~^ ERROR: this argument is a mutable reference, but not used mutably
+//~| NOTE: this is cfg-gated and may require further changes
 
 #[cfg(not(feature = "a"))]
 mod foo {
-    // Should warn with note.
     fn cfg_warn(s: &mut u32) {}
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
+    //~| NOTE: this is cfg-gated and may require further changes
 }
 
 fn main() {

tests/ui/needless_pass_by_ref_mut.stderr

@@ -1,5 +1,5 @@
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:7:11
+  --> $DIR/needless_pass_by_ref_mut.rs:6:11
    |
 LL | fn foo(s: &mut Vec<u32>, b: &u32, x: &mut u32) {
    |           ^^^^^^^^^^^^^ help: consider changing to: `&Vec<u32>`
@@ -7,79 +7,79 @@ LL | fn foo(s: &mut Vec<u32>, b: &u32, x: &mut u32) {
    = note: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:32:12
+  --> $DIR/needless_pass_by_ref_mut.rs:31:12
    |
 LL | fn foo6(s: &mut Vec<u32>) {
    |            ^^^^^^^^^^^^^ help: consider changing to: `&Vec<u32>`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:45:29
+  --> $DIR/needless_pass_by_ref_mut.rs:44:29
    |
 LL |     fn mushroom(&self, vec: &mut Vec<i32>) -> usize {
    |                             ^^^^^^^^^^^^^ help: consider changing to: `&Vec<i32>`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:50:31
+  --> $DIR/needless_pass_by_ref_mut.rs:49:31
    |
 LL |     fn badger(&mut self, vec: &mut Vec<i32>) -> usize {
    |                               ^^^^^^^^^^^^^ help: consider changing to: `&Vec<i32>`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:127:16
+  --> $DIR/needless_pass_by_ref_mut.rs:126:16
    |
 LL | async fn a1(x: &mut i32) {
    |                ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:131:16
+  --> $DIR/needless_pass_by_ref_mut.rs:130:16
    |
 LL | async fn a2(x: &mut i32, y: String) {
    |                ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:135:16
+  --> $DIR/needless_pass_by_ref_mut.rs:134:16
    |
 LL | async fn a3(x: &mut i32, y: String, z: String) {
    |                ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:139:16
+  --> $DIR/needless_pass_by_ref_mut.rs:138:16
    |
 LL | async fn a4(x: &mut i32, y: i32) {
    |                ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:143:24
+  --> $DIR/needless_pass_by_ref_mut.rs:142:24
    |
 LL | async fn a5(x: i32, y: &mut i32) {
    |                        ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:147:24
+  --> $DIR/needless_pass_by_ref_mut.rs:146:24
    |
 LL | async fn a6(x: i32, y: &mut i32) {
    |                        ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:151:32
+  --> $DIR/needless_pass_by_ref_mut.rs:150:32
    |
 LL | async fn a7(x: i32, y: i32, z: &mut i32) {
    |                                ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:155:24
+  --> $DIR/needless_pass_by_ref_mut.rs:154:24
    |
 LL | async fn a8(x: i32, a: &mut i32, y: i32, z: &mut i32) {
    |                        ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:155:45
+  --> $DIR/needless_pass_by_ref_mut.rs:154:45
    |
 LL | async fn a8(x: i32, a: &mut i32, y: i32, z: &mut i32) {
    |                                             ^^^^^^^^ help: consider changing to: `&i32`
 
 error: this argument is a mutable reference, but not used mutably
-  --> $DIR/needless_pass_by_ref_mut.rs:189:16
+  --> $DIR/needless_pass_by_ref_mut.rs:188:16
    |
 LL | fn cfg_warn(s: &mut u32) {}
    |                ^^^^^^^^ help: consider changing to: `&u32`