Add 'ast::PatKind::Rest'.

4 files changed, 18 insertions, 2 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index dbfad3ef7f4..37889c4918b 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -572,6 +572,7 @@ impl Pat {
                     && after.iter().all(|p| p.walk(it))
             }
             PatKind::Wild
+            | PatKind::Rest
             | PatKind::Lit(_)
             | PatKind::Range(..)
             | PatKind::Ident(..)
@@ -661,6 +662,20 @@ pub enum PatKind {
     ///     `PatKind::Slice(box [a, b], Some(i), box [y, z])`
     Slice(Vec<P<Pat>>, Option<P<Pat>>, Vec<P<Pat>>),
 
+    /// A rest pattern `..`.
+    ///
+    /// Syntactically it is valid anywhere.
+    ///
+    /// Semantically however, it only has meaning immediately inside:
+    /// - a slice pattern: `[a, .., b]`,
+    /// - a binding pattern immediately inside a slice pattern: `[a, r @ ..]`,
+    /// - a tuple pattern: `(a, .., b)`,
+    /// - a tuple struct/variant pattern: `$path(a, .., b)`.
+    ///
+    /// In all of these cases, an additional restriction applies,
+    /// only one rest pattern may occur in the pattern sequences.
+    Rest,
+
     /// Parentheses in patterns used for grouping (i.e., `(PAT)`).
     Paren(P<Pat>),
 
diff --git a/src/libsyntax/mut_visit.rs b/src/libsyntax/mut_visit.rs
index dc656222fbc..eb25956a769 100644
--- a/src/libsyntax/mut_visit.rs
+++ b/src/libsyntax/mut_visit.rs
@@ -1020,7 +1020,7 @@ pub fn noop_visit_pat<T: MutVisitor>(pat: &mut P<Pat>, vis: &mut T) {
     let Pat { id, node, span } = pat.deref_mut();
     vis.visit_id(id);
     match node {
-        PatKind::Wild => {}
+        PatKind::Wild | PatKind::Rest => {}
         PatKind::Ident(_binding_mode, ident, sub) => {
             vis.visit_ident(ident);
             visit_opt(sub, |sub| vis.visit_pat(sub));
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 16e0bace925..a067ae0e918 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -2478,6 +2478,7 @@ impl<'a> State<'a> {
                                    |s, p| s.print_pat(p));
                 self.s.word("]");
             }
+            PatKind::Rest => self.s.word(".."),
             PatKind::Paren(ref inner) => {
                 self.popen();
                 self.print_pat(inner);
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 9ec9550f93a..7c814bf3397 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -463,7 +463,7 @@ pub fn walk_pat<'a, V: Visitor<'a>>(visitor: &mut V, pattern: &'a Pat) {
             visitor.visit_expr(lower_bound);
             visitor.visit_expr(upper_bound);
         }
-        PatKind::Wild => (),
+        PatKind::Wild | PatKind::Rest => {},
         PatKind::Slice(ref prepatterns, ref slice_pattern, ref postpatterns) => {
             walk_list!(visitor, visit_pat, prepatterns);
             walk_list!(visitor, visit_pat, slice_pattern);