AST/HIR: Introduce ExprKind::Err for better error recovery in the front-end

src/libsyntax/util/parser.rs

@@ -267,6 +267,7 @@ pub enum ExprPrecedence {
     TryBlock,
     Struct,
     Async,
+    Err,
 }
 
 impl ExprPrecedence {
@@ -325,7 +326,8 @@ impl ExprPrecedence {
             ExprPrecedence::Block |
             ExprPrecedence::TryBlock |
             ExprPrecedence::Async |
-            ExprPrecedence::Struct => PREC_PAREN,
+            ExprPrecedence::Struct |
+            ExprPrecedence::Err => PREC_PAREN,
         }
     }
 }