[regexp] break recursion in mutually recursive capture/back references.

src/ast/ast.h

Index: src/ast/ast.h
diff --git a/src/ast/ast.h b/src/ast/ast.h
index b4f2992e047215ac95d2c61b96a98d64afbfb5a1..6a0393cb6cd76b7f12dca3840915ae727dafd8e5 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -3186,14 +3186,9 @@ class RegExpBackReference final : public RegExpTree {
   RegExpBackReference* AsBackReference() override;
   bool IsBackReference() override;
   int min_match() override { return 0; }
-  // The capture may not be completely parsed yet, if the reference occurs
-  // before the capture. In the ordinary case, nothing has been captured yet,
-  // so the back reference must have the length 0. If the back reference is
-  // inside a lookbehind, effectively making it a forward reference, we return
-  // 0 since lookbehinds have a length of 0.
-  int max_match() override {
-    return capture_->body() ? capture_->max_match() : 0;
-  }
+  // The back reference may be recursive, e.g. /(\2)(\1)/. To avoid infinite
+  // recursion, we give up. Ignorance is bliss.
+  int max_match() override { return kInfinity; }
   int index() { return capture_->index(); }
   RegExpCapture* capture() { return capture_; }
  private: