Support (..)

Author: varkor

compiler/rustc_ast_lowering/src/expr.rs

@@ -896,6 +896,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     true
                 }
             }
+            // `(..)`.
+            ExprKind::Paren(e) => {
+                if let ExprKind::Range(None, None, RangeLimits::HalfOpen) = e.kind {
+                    false
+                } else {
+                    true
+                }
+            }
             _ => true,
         };
         if is_ordinary {
@@ -1032,6 +1040,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 let tuple_pat = hir::PatKind::Tuple(pats, rest.map(|r| r.0));
                 return self.pat(lhs.span, tuple_pat);
             }
+            // `(..)`. We special-case this for consistency with declarations.
+            ExprKind::Paren(e) => {
+                if let ExprKind::Range(None, None, RangeLimits::HalfOpen) = e.kind {
+                    let tuple_pat = hir::PatKind::Tuple(&[], Some(0));
+                    return self.pat(lhs.span, tuple_pat);
+                }
+            }
             _ => {}
         }
         // Treat all other cases as normal lvalue.

src/test/ui/destructuring-assignment/tuple_destructure.rs

@@ -12,7 +12,6 @@ fn main() {
     assert_eq!((a, b), (1, 2));
     (_, a) = (1, 2);
     assert_eq!((a, b), (2, 2));
-    // The following currently does not work, but should.
-    // (..) = (3, 4);
-    // assert_eq!((a, b), (2, 2));
+    (..) = (3, 4);
+    assert_eq!((a, b), (2, 2));
 }