Add feature gate macro_lifetime_matcher

src/libsyntax/ext/tt/macro_rules.rs

@@ -886,8 +886,20 @@ fn is_legal_fragment_specifier(sess: &ParseSess,
                                frag_name: &str,
                                frag_span: Span) -> bool {
     match frag_name {
-        "item" | "block" | "stmt" | "expr" | "pat" | "lifetime" |
+        "item" | "block" | "stmt" | "expr" | "pat" |
         "path" | "ty" | "ident" | "meta" | "tt" | "" => true,
+        "lifetime" => {
+            if     !features.borrow().macro_lifetime_matcher
+                && !attr::contains_name(attrs, "allow_internal_unstable") {
+                let explain = feature_gate::EXPLAIN_LIFETIME_MATCHER;
+                emit_feature_err(sess,
+                                 "macro_lifetime_matcher",
+                                 frag_span,
+                                 GateIssue::Language,
+                                 explain);
+            }
+            true
+        },
         "vis" => {
             if     !features.borrow().macro_vis_matcher
                 && !attr::contains_name(attrs, "allow_internal_unstable") {

src/libsyntax/feature_gate.rs

@@ -447,6 +447,9 @@ declare_features! (
 
     // Termination trait in main (RFC 1937)
     (active, termination_trait, "1.24.0", Some(43301)),
+
+    // Allows use of the :lifetime macro fragment specifier
+    (active, macro_lifetime_matcher, "1.24.0", Some(46895)),
 );
 
 declare_features! (
@@ -520,7 +523,7 @@ declare_features! (
     (accepted, loop_break_value, "1.19.0", Some(37339)),
     // Permits numeric fields in struct expressions and patterns.
     (accepted, relaxed_adts, "1.19.0", Some(35626)),
-    // Coerces non capturing closures to function pointers
+   // Coerces non capturing closures to function pointers
     (accepted, closure_to_fn_coercion, "1.19.0", Some(39817)),
     // Allows attributes on struct literal fields.
     (accepted, struct_field_attributes, "1.20.0", Some(38814)),
@@ -1226,6 +1229,9 @@ pub const EXPLAIN_DERIVE_UNDERSCORE: &'static str =
 pub const EXPLAIN_VIS_MATCHER: &'static str =
     ":vis fragment specifier is experimental and subject to change";
 
+pub const EXPLAIN_LIFETIME_MATCHER: &'static str =
+    ":lifetime fragment specifier is experimental and subject to change";
+
 pub const EXPLAIN_PLACEMENT_IN: &'static str =
     "placement-in expression syntax is experimental and subject to change.";
 

src/test/run-pass/macro-lifetime-used-with-bound.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(macro_lifetime_matcher)]
+
 macro_rules! foo {
     ($l:lifetime, $l2:lifetime) => {
         fn f<$l: $l2, $l2>(arg: &$l str, arg2: &$l2 str) -> &$l str {

src/test/run-pass/macro-lifetime-used-with-labels.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![allow(unreachable_code)]
+#![feature(macro_lifetime_matcher)]
 
 macro_rules! x {
     ($a:lifetime) => {

src/test/run-pass/macro-lifetime-used-with-static.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(macro_lifetime_matcher)]
+
 macro_rules! foo {
     ($l:lifetime) => {
         fn f(arg: &$l str) -> &$l str {

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

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(macro_lifetime_matcher)]
+
 macro_rules! foo {
     ($l:lifetime) => {
         fn f<$l>(arg: &$l str) -> &$l str {

src/test/ui/feature-gate-macro-lifetime-matcher.rs

@@ -0,0 +1,19 @@
+// 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.
+
+// Test that the :lifetime macro fragment cannot be used when macro_lifetime_matcher
+// feature gate is not used.
+
+macro_rules! m { ($lt:lifetime) => {} }
+//~^ ERROR :lifetime fragment specifier is experimental and subject to change
+
+fn main() {
+    m!('a);
+}

src/test/ui/feature-gate-macro-lifetime-matcher.stderr

@@ -0,0 +1,10 @@
+error: :lifetime fragment specifier is experimental and subject to change (see issue #46895)
+  --> $DIR/feature-gate-macro-lifetime-matcher.rs:14:19
+   |
+14 | macro_rules! m { ($lt:lifetime) => {} }
+   |                   ^^^^^^^^^^^^
+   |
+   = help: add #![feature(macro_lifetime_matcher)] to the crate attributes to enable
+
+error: aborting due to previous error
+