Added feature gate (macro_hygiene_optout).

Author: Alexander Regueiro

src/libsyntax/ext/tt/macro_rules.rs

@@ -261,7 +261,7 @@ pub fn compile(sess: &ParseSess, features: &Features, def: &ast::Item) -> Syntax
                 if let MatchedNonterminal(ref nt) = *m {
                     if let NtTT(ref tt) = **nt {
                         return quoted::parse(tt.clone().into(),
-                                             !body.legacy,
+                                             !body.legacy && features.macro_hygiene_optout,
                                              false,
                                              sess,
                                              features,

src/libsyntax/feature_gate.rs

@@ -305,6 +305,9 @@ declare_features! (
     // Declarative macros 2.0 (`macro`).
     (active, decl_macro, "1.17.0", Some(39412), None),
 
+    // Hygiene opt-out (escaping) for macros 2.0 using `#ident` syntax.
+    (active, macro_hygiene_optout, "1.27.0", None, None),
+
     // Allows #[link(kind="static-nobundle"...]
     (active, static_nobundle, "1.16.0", Some(37403), None),
 

src/test/compile-fail/feature-gate-macro-hygiene-optout.rs

@@ -0,0 +1,22 @@
+// 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.
+
+#![feature(decl_macro)]
+
+macro m() {
+    pub mod #foo {
+    //~^ ERROR expected identifier, found `#`
+        pub const #BAR: u32 = 123;
+    }
+}
+
+fn main() {
+    m!();
+}

src/test/compile-fail/hygiene-optout-1.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![feature(decl_macro)]
+#![feature(macro_hygiene_optout)]
 
 macro m($mod_name:ident) {
     pub mod $mod_name {

src/test/compile-fail/hygiene-optout-2.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![feature(decl_macro)]
+#![feature(macro_hygiene_optout)]
 
 macro m() {
     pub mod #foo {

src/test/compile-fail/hygiene-optout-3.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![feature(decl_macro)]
+#![feature(macro_hygiene_optout)]
 
 macro m_helper() {
     struct #S;

src/test/compile-fail/hygiene-optout-4.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![feature(decl_macro)]
+#![feature(macro_hygiene_optout)]
 
 macro m() {
     struct #S;

src/test/compile-fail/hygiene-optout-5.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![feature(decl_macro)]
+#![feature(macro_hygiene_optout)]
 
 macro m($mod_name:ident) {
     pub mod $#mod_name {

src/test/run-pass/hygiene-optout-1.rs

@@ -9,14 +9,15 @@
 // except according to those terms.
 
 #![feature(decl_macro)]
+#![feature(macro_hygiene_optout)]
 
-macro m($mod_name:ident) {
-    pub mod #$mod_name {
+macro m() {
+    pub mod #foo {
         pub const #BAR: u32 = 123;
     }
 }
 
 fn main() {
-    m!(foo);
+    m!();
     assert_eq!(123, foo::BAR);
 }

src/test/run-pass/hygiene-optout-2.rs

@@ -9,14 +9,15 @@
 // except according to those terms.
 
 #![feature(decl_macro)]
+#![feature(macro_hygiene_optout)]
 
-macro m() {
-    pub mod #foo {
+macro m($mod_name:ident) {
+    pub mod #$mod_name {
         pub const #BAR: u32 = 123;
     }
 }
 
 fn main() {
-    m!();
+    m!(foo);
     assert_eq!(123, foo::BAR);
 }