Support syntax for one-line trait reuse

tests/pretty/delegation-impl-reuse.pp

@@ -0,0 +1,46 @@
+#![feature(prelude_import)]
+#![no_std]
+//@ pretty-compare-only
+//@ pretty-mode:expanded
+//@ pp-exact:delegation-impl-reuse.pp
+
+#![allow(incomplete_features)]
+#![feature(fn_delegation)]
+#[macro_use]
+extern crate std;
+#[prelude_import]
+use ::std::prelude::rust_2015::*;
+
+trait Trait<T> {
+    fn foo(&self) {}
+    fn bar(&self) {}
+    fn baz(&self) {}
+}
+
+struct S;
+
+impl Trait<{
+        struct S;
+        0
+    }> for S {
+    reuse Trait<{
+            struct S;
+            0
+        }>::foo {
+        self.0
+    }
+    reuse Trait<{
+            struct S;
+            0
+        }>::bar {
+        self.0
+    }
+    reuse Trait<{
+            struct S;
+            0
+        }>::baz {
+        self.0
+    }
+}
+
+fn main() {}

tests/pretty/delegation-impl-reuse.rs

@@ -0,0 +1,18 @@
+//@ pretty-compare-only
+//@ pretty-mode:expanded
+//@ pp-exact:delegation-impl-reuse.pp
+
+#![allow(incomplete_features)]
+#![feature(fn_delegation)]
+
+trait Trait<T> {
+    fn foo(&self) {}
+    fn bar(&self) {}
+    fn baz(&self) {}
+}
+
+struct S;
+
+reuse impl Trait<{ struct S; 0 }> for S { self.0 }
+
+fn main() {}