Suggest replacing _ in type signature of impl for Trait

src/test/ui/did_you_mean/replace-impl-infer-ty-from-trait.fixed

@@ -0,0 +1,13 @@
+// run-rustfix
+#![allow(unused)]
+
+trait Foo<T>: Sized {
+    fn bar(i: i32, t: T, s: &Self) {}
+}
+
+impl Foo<usize> for () {
+    fn bar(i: i32, t: usize, s: &()) {}
+    //~^ ERROR the placeholder `_` is not allowed within types on item signatures for functions
+}
+
+fn main() {}

src/test/ui/did_you_mean/replace-impl-infer-ty-from-trait.rs

@@ -0,0 +1,13 @@
+// run-rustfix
+#![allow(unused)]
+
+trait Foo<T>: Sized {
+    fn bar(i: i32, t: T, s: &Self) {}
+}
+
+impl Foo<usize> for () {
+    fn bar(i: _, t: _, s: _) {}
+    //~^ ERROR the placeholder `_` is not allowed within types on item signatures for functions
+}
+
+fn main() {}

src/test/ui/did_you_mean/replace-impl-infer-ty-from-trait.stderr

@@ -0,0 +1,17 @@
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for functions
+  --> $DIR/replace-impl-infer-ty-from-trait.rs:9:15
+   |
+LL |     fn bar(i: _, t: _, s: _) {}
+   |               ^     ^     ^ not allowed in type signatures
+   |               |     |
+   |               |     not allowed in type signatures
+   |               not allowed in type signatures
+   |
+help: try replacing `_` with the types in the corresponding trait method signature
+   |
+LL |     fn bar(i: i32, t: usize, s: &()) {}
+   |               ~~~     ~~~~~     ~~~
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0121`.

src/test/ui/typeck/typeck_type_placeholder_item.stderr

@@ -560,10 +560,10 @@ error[E0121]: the placeholder `_` is not allowed within types on item signatures
 LL |     fn clone_from(&mut self, other: _) { *self = Test9; }
    |                                     ^ not allowed in type signatures
    |
-help: use type parameters instead
+help: try replacing `_` with the type in the corresponding trait method signature
    |
-LL |     fn clone_from<T>(&mut self, other: T) { *self = Test9; }
-   |                  +++                   ~
+LL |     fn clone_from(&mut self, other: &Test9) { *self = Test9; }
+   |                                     ~~~~~~
 
 error[E0121]: the placeholder `_` is not allowed within types on item signatures for return types
   --> $DIR/typeck_type_placeholder_item.rs:107:31
@@ -600,10 +600,10 @@ error[E0121]: the placeholder `_` is not allowed within types on item signatures
 LL |         fn clone_from(&mut self, other: _) { *self = FnTest9; }
    |                                         ^ not allowed in type signatures
    |
-help: use type parameters instead
+help: try replacing `_` with the type in the corresponding trait method signature
    |
-LL |         fn clone_from<T>(&mut self, other: T) { *self = FnTest9; }
-   |                      +++                   ~
+LL |         fn clone_from(&mut self, other: &FnTest9) { *self = FnTest9; }
+   |                                         ~~~~~~~~
 
 error[E0121]: the placeholder `_` is not allowed within types on item signatures for associated types
   --> $DIR/typeck_type_placeholder_item.rs:201:14