Simplify scanner and generate better error message for legacy octals in templates

src/scanner.cc

 // Copyright 2011 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.
 
 // Features shared by parsing and pre-parsing scanners.
 
 #include <stdint.h>
 
 #include <cmath>
 
@@ skipping 715 matching lines @@
       break;
     }
     case 'v':
       c = '\v';
       break;
     case 'x': {
       c = ScanHexNumber<capture_raw>(2);
       if (c < 0) return false;
       break;
     }
-    case '0':
-      if (in_template_literal) {
-        // \ 0 DecimalDigit is never allowed in templates.
-        if (IsDecimalDigit(c0_)) {
-          Advance<capture_raw>();  // Advance to include the problematic char.
-          return false;
-        }
-
-        // The TV of TemplateCharacter :: \ EscapeSequence is the CV of
-        //     EscapeSequence.
-        // The CV of EscapeSequence :: 0 is the code unit value 0.
-        c = 0;
-        break;
-      }
-    // Fall through.
+    case '0':  // Fall through.
     case '1':  // fall through
     case '2':  // fall through
     case '3':  // fall through
     case '4':  // fall through
     case '5':  // fall through
     case '6':  // fall through
     case '7':
-      if (!in_template_literal) {
-        c = ScanOctalEscape<capture_raw>(c, 2);
-        break;
-      }
-    // Fall through
-    case '8':
-    case '9':
-      if (in_template_literal) return false;
+      c = ScanOctalEscape<capture_raw>(c, 2);
+      break;
   }
 
   // According to ECMA-262, section 7.8.4, characters not covered by the
   // above cases should be illegal, but they are commonly handled as
   // non-escaped characters by JS VMs.
   AddLiteralChar(c);
   return true;
 }
 
 
@@ skipping 722 matching lines @@
     }
     backing_store_.Add(static_cast<uint8_t>((one_byte_length >> 7) | 0x80u));
   }
   backing_store_.Add(static_cast<uint8_t>(one_byte_length & 0x7f));
 
   backing_store_.AddBlock(bytes);
   return backing_store_.EndSequence().start();
 }
 
 } }  // namespace v8::internal