syntax: Accept meta matchers in macros

This removes the `attr` matcher and adds a `meta` matcher. The previous `attr`
matcher is now ambiguous because it doesn't disambiguate whether it means inner
attribute or outer attribute.

The new behavior can still be achieved by taking an argument of the form
`#[$foo:meta]` (the brackets are part of the macro pattern).

Closes #13067

src/test/compile-fail/macro-inner-attributes.rs

@@ -11,8 +11,8 @@
 #[feature(macro_rules)];
 
 macro_rules! test ( ($nm:ident,
-                     $a:attr,
-                     $i:item) => (mod $nm { $a; $i }); )
+                     #[$a:meta],
+                     $i:item) => (mod $nm { #![$a] $i }); )
 
 test!(a,
       #[cfg(qux)],

src/test/compile-fail/macro-outer-attributes.rs

@@ -11,8 +11,8 @@
 #[feature(macro_rules)];
 
 macro_rules! test ( ($nm:ident,
-                     $a:attr,
-                     $i:item) => (mod $nm { $a $i }); )
+                     #[$a:meta],
+                     $i:item) => (mod $nm { #[$a] $i }); )
 
 test!(a,
       #[cfg(qux)],

src/test/run-pass/macro-attributes.rs

@@ -13,11 +13,11 @@
 #[feature(macro_rules)];
 
 macro_rules! compiles_fine {
-    ($at:attr) => {
+    (#[$at:meta]) => {
         // test that the different types of attributes work
         #[attribute]
         /// Documentation!
-        $at
+        #[$at]
 
         // check that the attributes are recognised by requiring this
         // to be removed to avoid a compile error

src/test/run-pass/macro-meta-items.rs

@@ -0,0 +1,43 @@
+// Copyright 2013-2014 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 - token trees can't pretty print
+// compile-flags: --cfg foo
+
+#[feature(macro_rules)];
+
+macro_rules! compiles_fine {
+    ($at:meta) => {
+        #[cfg($at)]
+        static MISTYPED: () = "foo";
+    }
+}
+macro_rules! emit {
+    ($at:meta) => {
+        #[cfg($at)]
+        static MISTYPED: &'static str = "foo";
+    }
+}
+
+// item
+compiles_fine!(bar)
+emit!(foo)
+
+fn foo() {
+    println!("{}", MISTYPED);
+}
+
+pub fn main() {
+    // statement
+    compiles_fine!(baz);
+    emit!(baz);
+    println!("{}", MISTYPED);
+}
+