review comments: more tests

src/test/ui/typeck/typeck_type_placeholder_item.rs

@@ -1,3 +1,4 @@
+#![feature(type_alias_impl_trait)] // Needed for single test `type Y = impl Trait<_>`
 // This test checks that it is not possible to enable global type
 // inference by using the `_` type placeholder.
 
@@ -42,6 +43,16 @@ impl Test9 {
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
 }
 
+fn test11(x: &usize) -> &_ {
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    &x
+}
+
+unsafe fn test12(x: *const usize) -> *const *const _ {
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+    &x
+}
+
 impl Clone for Test9 {
     fn clone(&self) -> _ { Test9 }
     //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
@@ -144,3 +155,24 @@ fn impl_trait() -> impl BadTrait<_> {
 //~^ ERROR the type placeholder `_` is not allowed within types on item signatures
     unimplemented!()
 }
+
+struct BadStruct1<_, _>(_);
+//~^ ERROR expected identifier, found reserved identifier `_`
+//~| ERROR expected identifier, found reserved identifier `_`
+//~| ERROR the name `_` is already used
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
+struct BadStruct2<_, T>(_, T);
+//~^ ERROR expected identifier, found reserved identifier `_`
+//~| ERROR the type placeholder `_` is not allowed within types on item signatures
+
+type X = Box<_>;
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+
+struct Struct;
+trait Trait<T> {}
+impl Trait<usize> for Struct {}
+type Y = impl Trait<_>;
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+fn foo() -> Y {
+    Struct
+}