[parser] Correctly handle invalid escapes in adjacent template tokens.

src/parsing/parser-base.h

 // Copyright 2012 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.
 
 #ifndef V8_PARSING_PARSER_BASE_H
 #define V8_PARSING_PARSER_BASE_H
 
 #include "src/ast/ast.h"
 #include "src/ast/scopes.h"
 #include "src/bailout-reason.h"
@@ skipping 817 matching lines @@
       impl()->ReportMessageAt(octal, message);
       scanner()->clear_octal_position();
       if (message == MessageTemplate::kStrictDecimalWithLeadingZero) {
         impl()->CountUsage(v8::Isolate::kDecimalWithLeadingZeroInStrictMode);
       }
       *ok = false;
     }
   }
 
   // Checks if an octal literal or an invalid hex or unicode escape sequence
-  // appears in a template literal. In the presence of such, either
-  // returns false or reports an error, depending on should_throw. Otherwise
-  // returns true.
+  // appears in the current template literal token. In the presence of such,
+  // either returns false or reports an error, depending on should_throw.
+  // Otherwise returns true.
   inline bool CheckTemplateEscapes(bool should_throw, bool* ok) {
+    DCHECK(scanner()->current_token() == Token::TEMPLATE_SPAN ||
+           scanner()->current_token() == Token::TEMPLATE_TAIL);
     if (!scanner()->has_invalid_template_escape()) {
       return true;
     }
 
     // Handle error case(s)
     if (should_throw) {
       impl()->ReportMessageAt(scanner()->invalid_template_escape_location(),
                               scanner()->invalid_template_escape_message());
       *ok = false;
     }
-    scanner()->clear_invalid_template_escape();
     return false;
   }
 
   void CheckDestructuringElement(ExpressionT element, int beg_pos, int end_pos);
 
   // Checking the name of a function literal. This has to be done after parsing
   // the function, since the function can declare itself strict.
   void CheckFunctionName(LanguageMode language_mode, IdentifierT function_name,
                          FunctionNameValidity function_name_validity,
                          const Scanner::Location& function_name_loc, bool* ok) {
@@ skipping 4983 matching lines @@
 }
 
 #undef CHECK_OK
 #undef CHECK_OK_CUSTOM
 #undef CHECK_OK_VOID
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_PARSER_BASE_H