Report unexpected lexical decl also without destructuring

src/parsing/parser-base.h

Index: src/parsing/parser-base.h
diff --git a/src/parsing/parser-base.h b/src/parsing/parser-base.h
index 126037823439150c746188a24b7c076c3e4cdb5d..a22ce83bd0c6a36f7edabab1b5a1b04224298b54 100644
--- a/src/parsing/parser-base.h
+++ b/src/parsing/parser-base.h
@@ -4932,12 +4932,16 @@ ParserBase<Impl>::ParseExpressionOrLabelledStatement(
       ReportUnexpectedToken(Next());
       *ok = false;
       return impl()->NullStatement();
-    case Token::LET:
-      if (PeekAhead() != Token::LBRACK) break;
+    case Token::LET: {
+      Token::Value next_next = PeekAhead();
+      // "let" followed by either "[" or an identifier means a lexical
+      // declaration, which should not appear here.
+      if (next_next != Token::LBRACK && next_next != Token::IDENTIFIER) break;

[Dan Ehrenberg, 2017/02/17 08:37:14]

Another case you can include here is "let {", which will not be syntactically
valid here and may come up as a destructuring case (by contrast, `let:` and `let
+ let` and `let()` are valid).

[vabr (Chromium), 2017/02/17 09:52:07]

Good idea! Done.

       impl()->ReportMessageAt(scanner()->peek_location(),
                               MessageTemplate::kUnexpectedLexicalDeclaration);
       *ok = false;
       return impl()->NullStatement();
+    }
     default:
       break;
   }