Simplify Scanner bookmarking.

src/parsing/scanner.cc

Index: src/parsing/scanner.cc
diff --git a/src/parsing/scanner.cc b/src/parsing/scanner.cc
index 60695a0bba7ce5a243bf2eb530d593428ddac588..325edbcd34003466d072ff8b88e5861cbda8fd2b 100644
--- a/src/parsing/scanner.cc
+++ b/src/parsing/scanner.cc
@@ -26,21 +26,60 @@ Handle<String> Scanner::LiteralBuffer::Internalize(Isolate* isolate) const {
   return isolate->factory()->InternalizeTwoByteString(two_byte_literal());
 }
 
+// ----------------------------------------------------------------------------
+// Scanner::BookmarkScope
+
+const size_t Scanner::BookmarkScope::kBookmarkAtFirstPos =
+    std::numeric_limits<size_t>::max() - 2;
+const size_t Scanner::BookmarkScope::kNoBookmark =
+    std::numeric_limits<size_t>::max() - 1;
+const size_t Scanner::BookmarkScope::kBookmarkWasApplied =
+    std::numeric_limits<size_t>::max();
+
+void Scanner::BookmarkScope::Set() {
+  DCHECK_EQ(bookmark_, kNoBookmark);
+  DCHECK_EQ(scanner_->next_next_.token, Token::UNINITIALIZED);
+
+  // The first token is a bit special, since current_ will still be
+  // uninitialized. In this case, store kBookmarkAtFirstPos and special-case it
+  // when
+  // applying the bookmark.
+  DCHECK_IMPLIES(
+      scanner_->current_.token == Token::UNINITIALIZED,
+      scanner_->current_.location.beg_pos == scanner_->next_.location.beg_pos);
+  bookmark_ = (scanner_->current_.token == Token::UNINITIALIZED)
+                  ? kBookmarkAtFirstPos
+                  : scanner_->location().beg_pos;
+}
+
+void Scanner::BookmarkScope::Apply() {
+  DCHECK(HasBeenSet());  // Caller hasn't called SetBookmark.
+  if (bookmark_ == kBookmarkAtFirstPos) {
+    scanner_->SeekNext(0);
+  } else {
+    scanner_->SeekNext(bookmark_);
+    scanner_->Next();
+    DCHECK_EQ(scanner_->location().beg_pos, bookmark_);
+  }
+  bookmark_ = kBookmarkWasApplied;
+}
+
+bool Scanner::BookmarkScope::HasBeenSet() {
+  return bookmark_ != kNoBookmark && bookmark_ != kBookmarkWasApplied;
+}
+
+bool Scanner::BookmarkScope::HasBeenApplied() {
+  return bookmark_ == kBookmarkWasApplied;
+}
 
 // ----------------------------------------------------------------------------
 // Scanner
 
 Scanner::Scanner(UnicodeCache* unicode_cache)
     : unicode_cache_(unicode_cache),
-      bookmark_c0_(kNoBookmark),
-      bookmark_position_(0),
       octal_pos_(Location::invalid()),
       decimal_with_leading_zero_pos_(Location::invalid()),
       found_html_comment_(false) {
-  bookmark_current_.literal_chars = &bookmark_current_literal_;
-  bookmark_current_.raw_literal_chars = &bookmark_current_raw_literal_;
-  bookmark_next_.literal_chars = &bookmark_next_literal_;
-  bookmark_next_.raw_literal_chars = &bookmark_next_raw_literal_;
 }
 
 
@@ -1581,56 +1620,24 @@ int Scanner::FindSymbol(DuplicateFinder* finder, int value) {
   return finder->AddTwoByteSymbol(literal_two_byte_string(), value);
 }
 
-void Scanner::SetBookmark() {
-  DCHECK_EQ(bookmark_c0_, kNoBookmark);
-  DCHECK_EQ(next_next_.token, Token::UNINITIALIZED);
-  bookmark_c0_ = c0_;
-  bookmark_position_ = source_->pos();
-  CopyTokenDesc(&bookmark_current_, &current_);
-  CopyTokenDesc(&bookmark_next_, &next_);
-}
-
-
-void Scanner::ResetToBookmark() {
-  DCHECK(BookmarkHasBeenSet());  // Caller hasn't called SetBookmark.
-
-  source_->Seek(bookmark_position_);
-  c0_ = bookmark_c0_;
-  CopyToNextTokenDesc(&bookmark_current_);
-  current_ = next_;
-  CopyToNextTokenDesc(&bookmark_next_);
-  bookmark_c0_ = kBookmarkWasApplied;
-}
-
-bool Scanner::BookmarkHasBeenSet() {
-  return bookmark_c0_ != kNoBookmark && bookmark_c0_ != kBookmarkWasApplied;
-}
-
-bool Scanner::BookmarkHasBeenReset() {
-  return bookmark_c0_ == kBookmarkWasApplied;
-}
-
-
-void Scanner::DropBookmark() { bookmark_c0_ = kNoBookmark; }
-
-void Scanner::CopyToNextTokenDesc(TokenDesc* from) {
-  StartLiteral();
-  StartRawLiteral();
-  CopyTokenDesc(&next_, from);
-  if (next_.literal_chars->length() == 0) next_.literal_chars = nullptr;
-  if (next_.raw_literal_chars->length() == 0) next_.raw_literal_chars = nullptr;
-}
-
-void Scanner::CopyTokenDesc(TokenDesc* to, TokenDesc* from) {
-  DCHECK_NOT_NULL(to);
-  DCHECK_NOT_NULL(from);
-  to->token = from->token;
-  to->location = from->location;
-  to->literal_chars->CopyFrom(from->literal_chars);
-  to->raw_literal_chars->CopyFrom(from->raw_literal_chars);
+void Scanner::SeekNext(size_t position) {
+  // Use with care: This cleanly resets most, but not all scanner state.
+  // TODO(vogelheim): Fix this, or at least DCHECK the relevant conditions.
+
+  // To re-scan from a given character position, we need to:
+  // 1, Reset the current_, next_ and next_next_ tokens
+  //    (next_ + next_next_ will be overwrittem by Next(),
+  //     current_ will remain unchanged, so overwrite it fully.)
+  current_ = {{0, 0}, nullptr, nullptr, 0, Token::UNINITIALIZED};
+  next_.token = Token::UNINITIALIZED;
+  next_next_.token = Token::UNINITIALIZED;
+  // 2, reset the source to the desired position,
+  source_->Seek(position);
+  // 3, re-scan, by scanning the look-ahead char + 1 token (next_).
+  c0_ = source_->Advance();
+  Next();
+  DCHECK_EQ(next_.location.beg_pos, position);
 }
 
-
-
 }  // namespace internal
 }  // namespace v8