Rollup merge of #48500 - petrochenkov:parpat, r=nikomatsakis

Support parentheses in patterns under feature gate

This is a prerequisite for any other extensions to pattern syntax - `|` with multiple patterns, type ascription, `..PAT` in slice patterns.

Closes https://github.com/rust-lang/rfcs/issues/554

1 files changed, 7 insertions, 0 deletions

diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 6444c846a8b..70ea015de4e 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -449,6 +449,9 @@ declare_features! (
 
     // Multiple patterns with `|` in `if let` and `while let`
     (active, if_while_or_patterns, "1.26.0", Some(48215)),
+
+    // Parentheses in patterns
+    (active, pattern_parentheses, "1.26.0", None),
 );
 
 declare_features! (
@@ -1663,6 +1666,10 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 gate_feature_post!(&self, dotdoteq_in_patterns, pattern.span,
                                    "`..=` syntax in patterns is experimental");
             }
+            PatKind::Paren(..) => {
+                gate_feature_post!(&self, pattern_parentheses, pattern.span,
+                                   "parentheses in patterns are unstable");
+            }
             _ => {}
         }
         visit::walk_pat(self, pattern)