Include RE2 library

third_party/re2/re2/testing/null_walker.cc

Index: third_party/re2/re2/testing/null_walker.cc
diff --git a/third_party/re2/re2/testing/null_walker.cc b/third_party/re2/re2/testing/null_walker.cc
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index 0000000000000000000000000000000000000000..09b53cbea3c0b285ea714103e04cbd62d6fa9e44
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+++ b/third_party/re2/re2/testing/null_walker.cc
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+// Copyright 2009 The RE2 Authors.  All Rights Reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "util/test.h"
+#include "re2/regexp.h"
+#include "re2/walker-inl.h"
+
+namespace re2 {
+
+// Null walker.  For benchmarking the walker itself.
+
+class NullWalker : public Regexp::Walker<bool> {
+ public:
+  NullWalker() { }
+  bool PostVisit(Regexp* re, bool parent_arg, bool pre_arg,
+                 bool* child_args, int nchild_args);
+
+  bool ShortVisit(Regexp* re, bool a) {
+    // Should never be called: we use Walk not WalkExponential.
+    LOG(DFATAL) << "NullWalker::ShortVisit called";
+    return a;
+  }
+
+ private:
+  DISALLOW_EVIL_CONSTRUCTORS(NullWalker);
+};
+
+// Called after visiting re's children.  child_args contains the return
+// value from each of the children's PostVisits (i.e., whether each child
+// can match an empty string).  Returns whether this clause can match an
+// empty string.
+bool NullWalker::PostVisit(Regexp* re, bool parent_arg, bool pre_arg,
+                                  bool* child_args, int nchild_args) {
+  return false;
+}
+
+// Returns whether re can match an empty string.
+void Regexp::NullWalk() {
+  NullWalker w;
+  w.Walk(this, false);
+}
+
+}  // namespace re2