Experimental support for RegExp lookbehind.

src/ast.cc

Index: src/ast.cc
diff --git a/src/ast.cc b/src/ast.cc
index b5c6cf57ea417cf8a70e266ac83bf82e72d31734..ed9b8d7bc6b72a17e619061b3e67284fe7bfa136 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -850,7 +850,7 @@ Interval RegExpDisjunction::CaptureRegisters() {
 }
 
 
-Interval RegExpLookahead::CaptureRegisters() {
+Interval RegExpLookaround::CaptureRegisters() {
   return body()->CaptureRegisters();
 }
 
@@ -918,8 +918,9 @@ bool RegExpDisjunction::IsAnchoredAtEnd() {
 }
 
 
-bool RegExpLookahead::IsAnchoredAtStart() {
-  return is_positive() && body()->IsAnchoredAtStart();
+bool RegExpLookaround::IsAnchoredAtStart() {
+  return is_positive() && read_direction() == READ_FORWARD &&
+         body()->IsAnchoredAtStart();
 }
 
 
@@ -1068,8 +1069,10 @@ void* RegExpUnparser::VisitCapture(RegExpCapture* that, void* data) {
 }
 
 
-void* RegExpUnparser::VisitLookahead(RegExpLookahead* that, void* data) {
-  os_ << "(-> " << (that->is_positive() ? "+ " : "- ");
+void* RegExpUnparser::VisitLookaround(RegExpLookaround* that, void* data) {
+  os_ << "(";
+  os_ << (that->read_direction() == RegExpTree::READ_FORWARD ? "->" : "<-");
+  os_ << (that->is_positive() ? " + " : " - ");
   that->body()->Accept(this, data);
   os_ << ")";
   return NULL;
@@ -1096,8 +1099,9 @@ std::ostream& RegExpTree::Print(std::ostream& os, Zone* zone) {  // NOLINT
 }
 
 
-RegExpDisjunction::RegExpDisjunction(ZoneList<RegExpTree*>* alternatives)
-    : alternatives_(alternatives) {
+RegExpDisjunction::RegExpDisjunction(ZoneList<RegExpTree*>* alternatives,
+                                     ReadDirection read_direction)
+    : RegExpTree(read_direction), alternatives_(alternatives) {
   DCHECK(alternatives->length() > 1);
   RegExpTree* first_alternative = alternatives->at(0);
   min_match_ = first_alternative->min_match();
@@ -1118,8 +1122,9 @@ static int IncreaseBy(int previous, int increase) {
   }
 }
 
-RegExpAlternative::RegExpAlternative(ZoneList<RegExpTree*>* nodes)
-    : nodes_(nodes) {
+RegExpAlternative::RegExpAlternative(ZoneList<RegExpTree*>* nodes,
+                                     ReadDirection read_direction)
+    : RegExpTree(read_direction), nodes_(nodes) {
   DCHECK(nodes->length() > 1);
   min_match_ = 0;
   max_match_ = 0;