[parser] Lift template literal invalid escape restriction

src/parsing/scanner.cc

Index: src/parsing/scanner.cc
diff --git a/src/parsing/scanner.cc b/src/parsing/scanner.cc
index 86aadcff9fae2e74e7e6d11172ab2aac91d4f62a..c1580bbeae7dd23d69d0e02c13b0090474cb1773 100644
--- a/src/parsing/scanner.cc
+++ b/src/parsing/scanner.cc
@@ -19,6 +19,46 @@
 namespace v8 {
 namespace internal {
 
+// Scoped helper for saving & restoring scanner error state.
+// This is used for tagged template literals, in which normally forbidden
+// escape sequences are allowed.
+class ErrorState {
+ public:
+  ErrorState(MessageTemplate::Template* message_stack,
+             Scanner::Location* location_stack)
+      : message_stack_(message_stack),
+        old_message_(*message_stack),
+        location_stack_(location_stack),
+        old_location_(*location_stack) {
+    *message_stack_ = MessageTemplate::kNone;
+    *location_stack_ = Scanner::Location::invalid();
+  }
+
+  ~ErrorState() {
+    *message_stack_ = old_message_;
+    *location_stack_ = old_location_;
+  }
+
+  void MoveErrorTo(MessageTemplate::Template* message_dest,
+                   Scanner::Location* location_dest) {
+    if (*message_stack_ == MessageTemplate::kNone) {
+      return;
+    }
+    if (*message_dest == MessageTemplate::kNone) {
+      *message_dest = *message_stack_;
+      *location_dest = *location_stack_;
+    }
+    *message_stack_ = MessageTemplate::kNone;
+    *location_stack_ = Scanner::Location::invalid();
+  }
+
+ private:
+  MessageTemplate::Template* const message_stack_;
+  MessageTemplate::Template const old_message_;
+  Scanner::Location* const location_stack_;
+  Scanner::Location const old_location_;
+};
+
 Handle<String> Scanner::LiteralBuffer::Internalize(Isolate* isolate) const {
   if (is_one_byte()) {
     return isolate->factory()->InternalizeOneByteString(one_byte_literal());
@@ -948,16 +988,12 @@ bool Scanner::ScanEscape() {
       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.
+  // Other escaped characters are interpreted as their non-escaped version.
   AddLiteralChar(c);
   return true;
 }
 
 
-// Octal escapes of the forms '\0xx' and '\xxx' are not a part of
-// ECMA-262. Other JS VMs support them.
 template <bool capture_raw>
 uc32 Scanner::ScanOctalEscape(uc32 c, int length) {
   uc32 x = c - '0';
@@ -1039,6 +1075,12 @@ Token::Value Scanner::ScanTemplateSpan() {
   // TEMPLATE_TAIL terminates a TemplateLiteral and does not need to be
   // followed by an Expression.
 
+  // These scoped helpers save and restore the original error state, so that we
+  // can specially treat invalid escape sequences in templates (which are
+  // handled by the parser).
+  ErrorState scanner_error_state(&scanner_error_, &scanner_error_location_);
+  ErrorState octal_error_state(&octal_message_, &octal_pos_);
+
   Token::Value result = Token::TEMPLATE_SPAN;
   LiteralScope literal(this);
   StartRawLiteral();
@@ -1069,8 +1111,16 @@ Token::Value Scanner::ScanTemplateSpan() {
             AddRawLiteralChar('\n');
           }
         }
-      } else if (!ScanEscape<capture_raw, in_template_literal>()) {
-        return Token::ILLEGAL;
+      } else {
+        bool success = ScanEscape<capture_raw, in_template_literal>();
+        USE(success);
+        DCHECK_EQ(!success, has_error());
+        // For templates, invalid escape sequence checking is handled in the
+        // parser.
+        scanner_error_state.MoveErrorTo(&invalid_template_escape_message_,
+                                        &invalid_template_escape_location_);
+        octal_error_state.MoveErrorTo(&invalid_template_escape_message_,
+                                      &invalid_template_escape_location_);
       }
     } else if (c < 0) {
       // Unterminated template literal
@@ -1095,6 +1145,7 @@ Token::Value Scanner::ScanTemplateSpan() {
   literal.Complete();
   next_.location.end_pos = source_pos();
   next_.token = result;
+
   return result;
 }