Do not yeet unsafe<> from type when formatting unsafe binder

src/tools/rustfmt/src/types.rs

@@ -1019,7 +1019,11 @@ impl Rewrite for ast::Ty {
             }
             ast::TyKind::UnsafeBinder(ref binder) => {
                 let mut result = String::new();
-                if let Some(ref lifetime_str) =
+                if binder.generic_params.is_empty() {
+                    // We always want to write `unsafe<>` since `unsafe<> Ty`
+                    // and `Ty` are distinct types.
+                    result.push_str("unsafe<> ")
+                } else if let Some(ref lifetime_str) =
                     rewrite_bound_params(context, shape, &binder.generic_params)
                 {
                     result.push_str("unsafe<");

src/tools/rustfmt/tests/source/unsafe-binders.rs

@@ -9,3 +9,6 @@ struct Foo {
 struct Bar(unsafe<'a> &'a ());
 
 impl Trait for unsafe<'a> &'a () {}
+
+fn empty()
+-> unsafe<> () {}

src/tools/rustfmt/tests/target/unsafe-binders.rs

@@ -7,3 +7,5 @@ struct Foo {
 struct Bar(unsafe<'a> &'a ());
 
 impl Trait for unsafe<'a> &'a () {}
+
+fn empty() -> unsafe<> () {}