Add test.

src/test/run-pass/hygiene/issue-47312.rs

@@ -0,0 +1,30 @@
+// 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.
+
+// ignore-pretty pretty-printing is unhygienic
+
+#![feature(decl_macro)]
+#![allow(unused)]
+
+mod foo {
+    pub macro m($s:tt, $i:tt) {
+        $s.$i
+    }
+}
+
+mod bar {
+    struct S(i32);
+    fn f() {
+        let s = S(0);
+        ::foo::m!(s, 0);
+    }
+}
+
+fn main() {}