Fix hygiene bug.

src/test/compile-fail-fulldeps/proc-macro/lints_in_proc_macros.rs

@@ -23,5 +23,5 @@ fn main() {
     bang_proc_macro2!();
     //~^ ERROR cannot find value `foobar2` in this scope
     //~^^ did you mean `foobar`?
-    println!("{}", x);
+    println!("{}", x); //~ ERROR cannot find value `x` in this scope
 }

src/test/run-pass-fulldeps/proc-macro/auxiliary/issue-42708.rs

@@ -0,0 +1,28 @@
+// 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.
+
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+#![feature(proc_macro)]
+
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+
+#[proc_macro_derive(Test)]
+pub fn derive(_input: TokenStream) -> TokenStream {
+    "fn f(s: S) { s.x }".parse().unwrap()
+}
+
+#[proc_macro_attribute]
+pub fn attr_test(_attr: TokenStream, input: TokenStream) -> TokenStream {
+    input
+}

src/test/run-pass-fulldeps/proc-macro/issue-42708.rs

@@ -0,0 +1,36 @@
+// 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.
+
+// aux-build:issue-42708.rs
+// ignore-stage1
+
+#![feature(decl_macro, proc_macro)]
+#![allow(unused)]
+
+extern crate issue_42708;
+
+macro m() {
+    #[derive(issue_42708::Test)]
+    struct S { x: () }
+
+    #[issue_42708::attr_test]
+    struct S2 { x: () }
+
+    #[derive(Clone)]
+    struct S3 { x: () }
+
+    fn g(s: S, s2: S2, s3: S3) {
+        (s.x, s2.x, s3.x);
+    }
+}
+
+m!();
+
+fn main() {}