added test

src/test/ui/impl-trait/universal-issue-48703.rs

@@ -0,0 +1,19 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(universal_impl_trait)]
+
+use std::fmt::Debug;
+
+fn foo<T>(x: impl Debug) { }
+
+fn main() {
+    foo::<String>('a'); //~ ERROR cannot provide explicit type parameters
+}

src/test/ui/impl-trait/universal-issue-48703.stderr

@@ -0,0 +1,9 @@
+error[E0632]: cannot provide explicit type parameters when `impl Trait` is used in argument position.
+  --> $DIR/universal-issue-48703.rs:18:5
+   |
+LL |     foo::<String>('a'); //~ ERROR cannot provide explicit type parameters
+   |     ^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0632`.