proc_macro: Fix crate root detection

src/test/ui-fulldeps/proc-macro/non-root.rs

@@ -0,0 +1,25 @@
+// Copyright 2018 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
+
+#![feature(proc_macro)]
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+use proc_macro::*;
+
+fn foo(arg: TokenStream) -> TokenStream {
+    #[proc_macro]
+    pub fn foo(arg: TokenStream) -> TokenStream { arg }
+    //~^ ERROR functions tagged with `#[proc_macro]` must currently reside in the root of the crate
+
+    arg
+}

src/test/ui-fulldeps/proc-macro/non-root.stderr

@@ -0,0 +1,8 @@
+error: functions tagged with `#[proc_macro]` must currently reside in the root of the crate
+  --> $DIR/non-root.rs:21:5
+   |
+LL |     pub fn foo(arg: TokenStream) -> TokenStream { arg }
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+