Add feature gate + tests

1 files changed, 8 insertions, 0 deletions

diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 9a2560b0458..9358511018a 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -452,6 +452,11 @@ declare_features! (
 
     // Allows `#[repr(transparent)]` attribute on newtype structs
     (active, repr_transparent, "1.25.0", Some(43036)),
+
+    // Use `?` as the Kleene "at most one" operator
+    // FIXME(mark-i-m): make sure we use the correct issue number when there is
+    //   a tracking issue...
+    (active, macro_at_most_once_rep, "1.25.0", None),
 );
 
 declare_features! (
@@ -1250,6 +1255,9 @@ pub const EXPLAIN_PLACEMENT_IN: &'static str =
 pub const EXPLAIN_UNSIZED_TUPLE_COERCION: &'static str =
     "Unsized tuple coercion is not stable enough for use and is subject to change";
 
+pub const EXPLAIN_MACRO_AT_MOST_ONCE_REP: &'static str =
+    "Using the `?` macro Kleene operator for \"at most one\" repetition is unstable";
+
 struct PostExpansionVisitor<'a> {
     context: &'a Context<'a>,
 }