Gracefully handle syntax errors in Parser::PatternRewriter.

src/parsing/pattern-rewriter.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/ast/ast.h"
 #include "src/messages.h"
 #include "src/parsing/parameter-initializer-rewriter.h"
 #include "src/parsing/parser.h"
 
 namespace v8 {
@@ skipping 32 matching lines @@
   rewriter.parser_ = parser;
   rewriter.context_ = ASSIGNMENT;
   rewriter.pattern_ = to_rewrite;
   rewriter.block_ = nullptr;
   rewriter.descriptor_ = nullptr;
   rewriter.names_ = nullptr;
   rewriter.ok_ = &ok;
   rewriter.recursion_level_ = 0;
 
   rewriter.RecurseIntoSubpattern(rewriter.pattern_, nullptr);
-  DCHECK(ok);
+  CHECK(ok);
 }
 
 
 Expression* Parser::PatternRewriter::RewriteDestructuringAssignment(
     Parser* parser, Assignment* assignment, Scope* scope) {
   DCHECK_NOT_NULL(assignment);
   DCHECK_EQ(Token::ASSIGN, assignment->op());
   auto to_rewrite =
       parser->factory()->NewRewritableAssignmentExpression(assignment);
   RewriteDestructuringAssignment(parser, to_rewrite, scope);
@@ skipping 504 matching lines @@
       zone());
 }
 
 
 // =============== UNREACHABLE =============================
 
 void Parser::PatternRewriter::Visit(AstNode* node) { UNREACHABLE(); }
 
 #define NOT_A_PATTERN(Node)                                        \
   void Parser::PatternRewriter::Visit##Node(v8::internal::Node*) { \
-    UNREACHABLE();                                                 \
+    parser_->ReportMessage(MessageTemplate::kUnsupported);         \
+    *ok_ = false;                                                  \
   }
 
 NOT_A_PATTERN(BinaryOperation)
 NOT_A_PATTERN(Block)
 NOT_A_PATTERN(BreakStatement)
 NOT_A_PATTERN(Call)
 NOT_A_PATTERN(CallNew)
 NOT_A_PATTERN(CallRuntime)
 NOT_A_PATTERN(CaseClause)
 NOT_A_PATTERN(ClassLiteral)
@@ skipping 30 matching lines @@
 NOT_A_PATTERN(TryFinallyStatement)
 NOT_A_PATTERN(UnaryOperation)
 NOT_A_PATTERN(VariableDeclaration)
 NOT_A_PATTERN(WhileStatement)
 NOT_A_PATTERN(WithStatement)
 NOT_A_PATTERN(Yield)
 
 #undef NOT_A_PATTERN
 }  // namespace internal
 }  // namespace v8