Implement a 'trial parse' step, that will abort pre-parsing excessively

src/scanner.cc

Index: src/scanner.cc
diff --git a/src/scanner.cc b/src/scanner.cc
index 1dae1e42cd4c8f726cf95916205066782dc35fcd..8e26423e3228ee9a55ae664c00af8cba65d0ee3a 100644
--- a/src/scanner.cc
+++ b/src/scanner.cc
@@ -29,15 +29,26 @@ Handle<String> LiteralBuffer::Internalize(Isolate* isolate) const {
 }
 
 
+// Default implementation for streams that do not support bookmarks.
+bool Utf16CharacterStream::SetBookmark() { return false; }
+void Utf16CharacterStream::ResetToBookmark() { UNREACHABLE(); }
+
+
 // ----------------------------------------------------------------------------
 // Scanner
 
 Scanner::Scanner(UnicodeCache* unicode_cache)
     : unicode_cache_(unicode_cache),
+      bookmark_c0_(-1),
       octal_pos_(Location::invalid()),
       harmony_modules_(false),
       harmony_classes_(false),
-      harmony_unicode_(false) {}
+      harmony_unicode_(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_;
+}
 
 
 void Scanner::Initialize(Utf16CharacterStream* source) {
@@ -1426,6 +1437,53 @@ int Scanner::FindSymbol(DuplicateFinder* finder, int value) {
 }
 
 
+bool Scanner::SetBookmark() {
+  if (bookmark_c0_ == -1 && source_->SetBookmark()) {
+    bookmark_c0_ = c0_;
+    CopyTokenDesc(&bookmark_current_, &current_);
+    CopyTokenDesc(&bookmark_next_, &next_);
+    return true;
+  }
+  return false;
+}
+
+
+void Scanner::ResetToBookmark() {
+  DCHECK(bookmark_c0_ >= 0);  // Caller hasn't called SetBookmark.
+
+  source_->ResetToBookmark();
+  c0_ = bookmark_c0_;
+  StartLiteral();
+  StartRawLiteral();
+  CopyTokenDesc(&next_, &bookmark_current_);
+  current_ = next_;
+  StartLiteral();
+  StartRawLiteral();
+  CopyTokenDesc(&next_, &bookmark_next_);
+
+  bookmark_c0_ = -2;
+}
+
+
+bool Scanner::BookmarkHasBeenSet() { return bookmark_c0_ >= 0; }
+
+
+bool Scanner::BookmarkHasBeenReset() { return bookmark_c0_ == -2; }
+
+
+void Scanner::DropBookmark() { bookmark_c0_ = -1; }
+
+
+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);
+}
+
+
 int DuplicateFinder::AddOneByteSymbol(Vector<const uint8_t> key, int value) {
   return AddSymbol(key, true, value);
 }