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+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Author: jschorr@google.com (Joseph Schorr)
+//  Based on original Protocol Buffers design by
+//  Sanjay Ghemawat, Jeff Dean, and others.
+//
+// This file defines static methods and classes for comparing Protocol
+// Messages.
+//
+// Aug. 2008: Added Unknown Fields Comparison for messages.
+// Aug. 2009: Added different options to compare repeated fields.
+// Apr. 2010: Moved field comparison to FieldComparator
+// Sep. 2020: Added option to output map keys in path
+
+#ifndef GOOGLE_PROTOBUF_UTIL_MESSAGE_DIFFERENCER_H__
+#define GOOGLE_PROTOBUF_UTIL_MESSAGE_DIFFERENCER_H__
+
+
+#include <functional>
+#include <map>
+#include <memory>
+#include <set>
+#include <string>
+#include <vector>
+
+#include <google/protobuf/descriptor.h>  // FieldDescriptor
+#include <google/protobuf/message.h>     // Message
+#include <google/protobuf/unknown_field_set.h>
+#include <google/protobuf/util/field_comparator.h>
+
+// Always include as last one, otherwise it can break compilation
+#include <google/protobuf/port_def.inc>
+
+namespace google {
+namespace protobuf {
+
+class DynamicMessageFactory;
+class FieldDescriptor;
+
+namespace io {
+class ZeroCopyOutputStream;
+class Printer;
+}  // namespace io
+
+namespace util {
+
+class DefaultFieldComparator;
+class FieldContext;  // declared below MessageDifferencer
+
+// Defines a collection of field descriptors.
+// In case of internal google codebase we are using absl::FixedArray instead
+// of vector. It significantly speeds up proto comparison (by ~30%) by
+// reducing the number of malloc/free operations
+typedef std::vector<const FieldDescriptor*> FieldDescriptorArray;
+
+// A basic differencer that can be used to determine
+// the differences between two specified Protocol Messages. If any differences
+// are found, the Compare method will return false, and any differencer reporter
+// specified via ReportDifferencesTo will have its reporting methods called (see
+// below for implementation of the report). Based off of the original
+// ProtocolDifferencer implementation in //net/proto/protocol-differencer.h
+// (Thanks Todd!).
+//
+// MessageDifferencer REQUIRES that compared messages be the same type, defined
+// as messages that share the same descriptor.  If not, the behavior of this
+// class is undefined.
+//
+// People disagree on what MessageDifferencer should do when asked to compare
+// messages with different descriptors.  Some people think it should always
+// return false.  Others expect it to try to look for similar fields and
+// compare them anyway -- especially if the descriptors happen to be identical.
+// If we chose either of these behaviors, some set of people would find it
+// surprising, and could end up writing code expecting the other behavior
+// without realizing their error.  Therefore, we forbid that usage.
+//
+// This class is implemented based on the proto2 reflection. The performance
+// should be good enough for normal usages. However, for places where the
+// performance is extremely sensitive, there are several alternatives:
+// - Comparing serialized string
+// Downside: false negatives (there are messages that are the same but their
+// serialized strings are different).
+// - Equals code generator by compiler plugin (net/proto2/contrib/equals_plugin)
+// Downside: more generated code; maintenance overhead for the additional rule
+// (must be in sync with the original proto_library).
+//
+// Note on handling of google.protobuf.Any: MessageDifferencer automatically
+// unpacks Any::value into a Message and compares its individual fields.
+// Messages encoded in a repeated Any cannot be compared using TreatAsMap.
+//
+// Note on thread-safety: MessageDifferencer is *not* thread-safe. You need to
+// guard it with a lock to use the same MessageDifferencer instance from
+// multiple threads. Note that it's fine to call static comparison methods
+// (like MessageDifferencer::Equals) concurrently, but it's not recommended for
+// performance critical code as it leads to extra allocations.
+class PROTOBUF_EXPORT MessageDifferencer {
+ public:
+  // Determines whether the supplied messages are equal. Equality is defined as
+  // all fields within the two messages being set to the same value. Primitive
+  // fields and strings are compared by value while embedded messages/groups
+  // are compared as if via a recursive call. Use Compare() with IgnoreField()
+  // if some fields should be ignored in the comparison. Use Compare() with
+  // TreatAsSet() if there are repeated fields where ordering does not matter.
+  //
+  // This method REQUIRES that the two messages have the same
+  // Descriptor (message1.GetDescriptor() == message2.GetDescriptor()).
+  static bool Equals(const Message& message1, const Message& message2);
+
+  // Determines whether the supplied messages are equivalent. Equivalency is
+  // defined as all fields within the two messages having the same value. This
+  // differs from the Equals method above in that fields with default values
+  // are considered set to said value automatically. For details on how default
+  // values are defined for each field type, see:
+  // https://developers.google.com/protocol-buffers/docs/proto?csw=1#optional.
+  // Also, Equivalent() ignores unknown fields. Use IgnoreField() and Compare()
+  // if some fields should be ignored in the comparison.
+  //
+  // This method REQUIRES that the two messages have the same
+  // Descriptor (message1.GetDescriptor() == message2.GetDescriptor()).
+  static bool Equivalent(const Message& message1, const Message& message2);
+
+  // Determines whether the supplied messages are approximately equal.
+  // Approximate equality is defined as all fields within the two messages
+  // being approximately equal.  Primitive (non-float) fields and strings are
+  // compared by value, floats are compared using MathUtil::AlmostEquals() and
+  // embedded messages/groups are compared as if via a recursive call. Use
+  // IgnoreField() and Compare() if some fields should be ignored in the
+  // comparison.
+  //
+  // This method REQUIRES that the two messages have the same
+  // Descriptor (message1.GetDescriptor() == message2.GetDescriptor()).
+  static bool ApproximatelyEquals(const Message& message1,
+                                  const Message& message2);
+
+  // Determines whether the supplied messages are approximately equivalent.
+  // Approximate equivalency is defined as all fields within the two messages
+  // being approximately equivalent. As in
+  // MessageDifferencer::ApproximatelyEquals, primitive (non-float) fields and
+  // strings are compared by value, floats are compared using
+  // MathUtil::AlmostEquals() and embedded messages/groups are compared as if
+  // via a recursive call. However, fields with default values are considered
+  // set to said value, as per MessageDiffencer::Equivalent. Use IgnoreField()
+  // and Compare() if some fields should be ignored in the comparison.
+  //
+  // This method REQUIRES that the two messages have the same
+  // Descriptor (message1.GetDescriptor() == message2.GetDescriptor()).
+  static bool ApproximatelyEquivalent(const Message& message1,
+                                      const Message& message2);
+
+  // Identifies an individual field in a message instance.  Used for field_path,
+  // below.
+  struct SpecificField {
+    // For known fields, "field" is filled in and "unknown_field_number" is -1.
+    // For unknown fields, "field" is NULL, "unknown_field_number" is the field
+    // number, and "unknown_field_type" is its type.
+    const FieldDescriptor* field = nullptr;
+    int unknown_field_number = -1;
+    UnknownField::Type unknown_field_type = UnknownField::Type::TYPE_VARINT;
+
+    // If this a repeated field, "index" is the index within it.  For unknown
+    // fields, this is the index of the field among all unknown fields of the
+    // same field number and type.
+    int index = -1;
+
+    // If "field" is a repeated field which is being treated as a map or
+    // a set (see TreatAsMap() and TreatAsSet(), below), new_index indicates
+    // the index the position to which the element has moved.  If the element
+    // has not moved, "new_index" will have the same value as "index".
+    int new_index = -1;
+
+    // If "field" is a map field, point to the map entry.
+    const Message* map_entry1 = nullptr;
+    const Message* map_entry2 = nullptr;
+
+    // For unknown fields, these are the pointers to the UnknownFieldSet
+    // containing the unknown fields. In certain cases (e.g. proto1's
+    // MessageSet, or nested groups of unknown fields), these may differ from
+    // the messages' internal UnknownFieldSets.
+    const UnknownFieldSet* unknown_field_set1 = nullptr;
+    const UnknownFieldSet* unknown_field_set2 = nullptr;
+
+    // For unknown fields, these are the index of the field within the
+    // UnknownFieldSets. One or the other will be -1 when
+    // reporting an addition or deletion.
+    int unknown_field_index1 = -1;
+    int unknown_field_index2 = -1;
+  };
+
+  // Abstract base class from which all MessageDifferencer
+  // reporters derive. The five Report* methods below will be called when
+  // a field has been added, deleted, modified, moved, or matched. The third
+  // argument is a vector of FieldDescriptor pointers which describes the chain
+  // of fields that was taken to find the current field. For example, for a
+  // field found in an embedded message, the vector will contain two
+  // FieldDescriptors. The first will be the field of the embedded message
+  // itself and the second will be the actual field in the embedded message
+  // that was added/deleted/modified.
+  // Fields will be reported in PostTraversalOrder.
+  // For example, given following proto, if both baz and mooo are changed.
+  // foo {
+  //   bar {
+  //     baz: 1
+  //     mooo: 2
+  //   }
+  // }
+  // ReportModified will be invoked with following order:
+  // 1. foo.bar.baz or foo.bar.mooo
+  // 2. foo.bar.mooo or foo.bar.baz
+  // 2. foo.bar
+  // 3. foo
+  class PROTOBUF_EXPORT Reporter {
+   public:
+    Reporter();
+    virtual ~Reporter();
+
+    // Reports that a field has been added into Message2.
+    virtual void ReportAdded(const Message& message1, const Message& message2,
+                             const std::vector<SpecificField>& field_path) = 0;
+
+    // Reports that a field has been deleted from Message1.
+    virtual void ReportDeleted(
+        const Message& message1, const Message& message2,
+        const std::vector<SpecificField>& field_path) = 0;
+
+    // Reports that the value of a field has been modified.
+    virtual void ReportModified(
+        const Message& message1, const Message& message2,
+        const std::vector<SpecificField>& field_path) = 0;
+
+    // Reports that a repeated field has been moved to another location.  This
+    // only applies when using TreatAsSet or TreatAsMap()  -- see below. Also
+    // note that for any given field, ReportModified and ReportMoved are
+    // mutually exclusive. If a field has been both moved and modified, then
+    // only ReportModified will be called.
+    virtual void ReportMoved(
+        const Message& /* message1 */, const Message& /* message2 */,
+        const std::vector<SpecificField>& /* field_path */) {}
+
+    // Reports that two fields match. Useful for doing side-by-side diffs.
+    // This function is mutually exclusive with ReportModified and ReportMoved.
+    // Note that you must call set_report_matches(true) before calling Compare
+    // to make use of this function.
+    virtual void ReportMatched(
+        const Message& /* message1 */, const Message& /* message2 */,
+        const std::vector<SpecificField>& /* field_path */) {}
+
+    // Reports that two fields would have been compared, but the
+    // comparison has been skipped because the field was marked as
+    // 'ignored' using IgnoreField().  This function is mutually
+    // exclusive with all the other Report() functions.
+    //
+    // The contract of ReportIgnored is slightly different than the
+    // other Report() functions, in that |field_path.back().index| is
+    // always equal to -1, even if the last field is repeated. This is
+    // because while the other Report() functions indicate where in a
+    // repeated field the action (Addition, Deletion, etc...)
+    // happened, when a repeated field is 'ignored', the differencer
+    // simply calls ReportIgnored on the repeated field as a whole and
+    // moves on without looking at its individual elements.
+    //
+    // Furthermore, ReportIgnored() does not indicate whether the
+    // fields were in fact equal or not, as Compare() does not inspect
+    // these fields at all. It is up to the Reporter to decide whether
+    // the fields are equal or not (perhaps with a second call to
+    // Compare()), if it cares.
+    virtual void ReportIgnored(
+        const Message& /* message1 */, const Message& /* message2 */,
+        const std::vector<SpecificField>& /* field_path */) {}
+
+    // Report that an unknown field is ignored. (see comment above).
+    // Note this is a different function since the last SpecificField in field
+    // path has a null field.  This could break existing Reporter.
+    virtual void ReportUnknownFieldIgnored(
+        const Message& /* message1 */, const Message& /* message2 */,
+        const std::vector<SpecificField>& /* field_path */) {}
+
+   private:
+    GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(Reporter);
+  };
+
+  // MapKeyComparator is used to determine if two elements have the same key
+  // when comparing elements of a repeated field as a map.
+  class PROTOBUF_EXPORT MapKeyComparator {
+   public:
+    MapKeyComparator();
+    virtual ~MapKeyComparator();
+
+    virtual bool IsMatch(
+        const Message& /* message1 */, const Message& /* message2 */,
+        const std::vector<SpecificField>& /* parent_fields */) const {
+      GOOGLE_CHECK(false) << "IsMatch() is not implemented.";
+      return false;
+    }
+
+   private:
+    GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MapKeyComparator);
+  };
+
+  // Abstract base class from which all IgnoreCriteria derive.
+  // By adding IgnoreCriteria more complex ignore logic can be implemented.
+  // IgnoreCriteria are registered with AddIgnoreCriteria. For each compared
+  // field IsIgnored is called on each added IgnoreCriteria until one returns
+  // true or all return false.
+  // IsIgnored is called for fields where at least one side has a value.
+  class PROTOBUF_EXPORT IgnoreCriteria {
+   public:
+    IgnoreCriteria();
+    virtual ~IgnoreCriteria();
+
+    // Returns true if the field should be ignored.
+    virtual bool IsIgnored(
+        const Message& /* message1 */, const Message& /* message2 */,
+        const FieldDescriptor* /* field */,
+        const std::vector<SpecificField>& /* parent_fields */) = 0;
+
+    // Returns true if the unknown field should be ignored.
+    // Note: This will be called for unknown fields as well in which case
+    //       field.field will be null.
+    virtual bool IsUnknownFieldIgnored(
+        const Message& /* message1 */, const Message& /* message2 */,
+        const SpecificField& /* field */,
+        const std::vector<SpecificField>& /* parent_fields */) {
+      return false;
+    }
+  };
+
+  // To add a Reporter, construct default here, then use ReportDifferencesTo or
+  // ReportDifferencesToString.
+  explicit MessageDifferencer();
+
+  ~MessageDifferencer();
+
+  enum MessageFieldComparison {
+    EQUAL,       // Fields must be present in both messages
+                 // for the messages to be considered the same.
+    EQUIVALENT,  // Fields with default values are considered set
+                 // for comparison purposes even if not explicitly
+                 // set in the messages themselves.  Unknown fields
+                 // are ignored.
+  };
+
+  enum Scope {
+    FULL,    // All fields of both messages are considered in the comparison.
+    PARTIAL  // Only fields present in the first message are considered; fields
+             // set only in the second message will be skipped during
+             // comparison.
+  };
+
+  // DEPRECATED. Use FieldComparator::FloatComparison instead.
+  enum FloatComparison {
+    EXACT,       // Floats and doubles are compared exactly.
+    APPROXIMATE  // Floats and doubles are compared using the
+                 // MathUtil::AlmostEquals method.
+  };
+
+  enum RepeatedFieldComparison {
+    AS_LIST,  // Repeated fields are compared in order.  Differing values at
+              // the same index are reported using ReportModified().  If the
+              // repeated fields have different numbers of elements, the
+              // unpaired elements are reported using ReportAdded() or
+              // ReportDeleted().
+    AS_SET,   // Treat all the repeated fields as sets.
+              // See TreatAsSet(), as below.
+    AS_SMART_LIST,  // Similar to AS_SET, but preserve the order and find the
+                    // longest matching sequence from the first matching
+                    // element. To use an optimal solution, call
+                    // SetMatchIndicesForSmartListCallback() to pass it in.
+    AS_SMART_SET,   // Similar to AS_SET, but match elements with fewest diffs.
+  };
+
+  // The elements of the given repeated field will be treated as a set for
+  // diffing purposes, so different orderings of the same elements will be
+  // considered equal.  Elements which are present on both sides of the
+  // comparison but which have changed position will be reported with
+  // ReportMoved().  Elements which only exist on one side or the other are
+  // reported with ReportAdded() and ReportDeleted() regardless of their
+  // positions.  ReportModified() is never used for this repeated field.  If
+  // the only differences between the compared messages is that some fields
+  // have been moved, then the comparison returns true.
+  //
+  // Note that despite the name of this method, this is really
+  // comparison as multisets: if one side of the comparison has a duplicate
+  // in the repeated field but the other side doesn't, this will count as
+  // a mismatch.
+  //
+  // If the scope of comparison is set to PARTIAL, then in addition to what's
+  // above, extra values added to repeated fields of the second message will
+  // not cause the comparison to fail.
+  //
+  // Note that set comparison is currently O(k * n^2) (where n is the total
+  // number of elements, and k is the average size of each element). In theory
+  // it could be made O(n * k) with a more complex hashing implementation. Feel
+  // free to contribute one if the current implementation is too slow for you.
+  // If partial matching is also enabled, the time complexity will be O(k * n^2
+  // + n^3) in which n^3 is the time complexity of the maximum matching
+  // algorithm.
+  //
+  // REQUIRES: field->is_repeated() and field not registered with TreatAsMap*
+  void TreatAsSet(const FieldDescriptor* field);
+  void TreatAsSmartSet(const FieldDescriptor* field);
+
+  // The elements of the given repeated field will be treated as a list for
+  // diffing purposes, so different orderings of the same elements will NOT be
+  // considered equal.
+  //
+  // REQUIRES: field->is_repeated() and field not registered with TreatAsMap*
+  void TreatAsList(const FieldDescriptor* field);
+  // Note that the complexity is similar to treating as SET.
+  void TreatAsSmartList(const FieldDescriptor* field);
+
+  // The elements of the given repeated field will be treated as a map for
+  // diffing purposes, with |key| being the map key.  Thus, elements with the
+  // same key will be compared even if they do not appear at the same index.
+  // Differences are reported similarly to TreatAsSet(), except that
+  // ReportModified() is used to report elements with the same key but
+  // different values.  Note that if an element is both moved and modified,
+  // only ReportModified() will be called.  As with TreatAsSet, if the only
+  // differences between the compared messages is that some fields have been
+  // moved, then the comparison returns true. See TreatAsSet for notes on
+  // performance.
+  //
+  // REQUIRES:  field->is_repeated()
+  // REQUIRES:  field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE
+  // REQUIRES:  key->containing_type() == field->message_type()
+  void TreatAsMap(const FieldDescriptor* field, const FieldDescriptor* key);
+  // Same as TreatAsMap except that this method will use multiple fields as
+  // the key in comparison. All specified fields in 'key_fields' should be
+  // present in the compared elements. Two elements will be treated as having
+  // the same key iff they have the same value for every specified field. There
+  // are two steps in the comparison process. The first one is key matching.
+  // Every element from one message will be compared to every element from
+  // the other message. Only fields in 'key_fields' are compared in this step
+  // to decide if two elements have the same key. The second step is value
+  // comparison. Those pairs of elements with the same key (with equal value
+  // for every field in 'key_fields') will be compared in this step.
+  // Time complexity of the first step is O(s * m * n ^ 2) where s is the
+  // average size of the fields specified in 'key_fields', m is the number of
+  // fields in 'key_fields' and n is the number of elements. If partial
+  // matching is enabled, an extra O(n^3) will be incured by the maximum
+  // matching algorithm. The second step is O(k * n) where k is the average
+  // size of each element.
+  void TreatAsMapWithMultipleFieldsAsKey(
+      const FieldDescriptor* field,
+      const std::vector<const FieldDescriptor*>& key_fields);
+  // Same as TreatAsMapWithMultipleFieldsAsKey, except that each of the field
+  // do not necessarily need to be a direct subfield. Each element in
+  // key_field_paths indicate a path from the message being compared, listing
+  // successive subfield to reach the key field.
+  //
+  // REQUIRES:
+  //   for key_field_path in key_field_paths:
+  //     key_field_path[0]->containing_type() == field->message_type()
+  //     for i in [0, key_field_path.size() - 1):
+  //       key_field_path[i+1]->containing_type() ==
+  //           key_field_path[i]->message_type()
+  //       key_field_path[i]->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE
+  //       !key_field_path[i]->is_repeated()
+  void TreatAsMapWithMultipleFieldPathsAsKey(
+      const FieldDescriptor* field,
+      const std::vector<std::vector<const FieldDescriptor*> >& key_field_paths);
+
+  // Uses a custom MapKeyComparator to determine if two elements have the same
+  // key when comparing a repeated field as a map.
+  // The caller is responsible to delete the key_comparator.
+  // This method varies from TreatAsMapWithMultipleFieldsAsKey only in the
+  // first key matching step. Rather than comparing some specified fields, it
+  // will invoke the IsMatch method of the given 'key_comparator' to decide if
+  // two elements have the same key.
+  void TreatAsMapUsingKeyComparator(const FieldDescriptor* field,
+                                    const MapKeyComparator* key_comparator);
+
+  // Initiates and returns a new instance of MultipleFieldsMapKeyComparator.
+  MapKeyComparator* CreateMultipleFieldsMapKeyComparator(
+      const std::vector<std::vector<const FieldDescriptor*> >& key_field_paths);
+
+  // Add a custom ignore criteria that is evaluated in addition to the
+  // ignored fields added with IgnoreField.
+  // Takes ownership of ignore_criteria.
+  void AddIgnoreCriteria(IgnoreCriteria* ignore_criteria);
+
+  // Indicates that any field with the given descriptor should be
+  // ignored for the purposes of comparing two messages. This applies
+  // to fields nested in the message structure as well as top level
+  // ones. When the MessageDifferencer encounters an ignored field,
+  // ReportIgnored is called on the reporter, if one is specified.
+  //
+  // The only place where the field's 'ignored' status is not applied is when
+  // it is being used as a key in a field passed to TreatAsMap or is one of
+  // the fields passed to TreatAsMapWithMultipleFieldsAsKey.
+  // In this case it is compared in key matching but after that it's ignored
+  // in value comparison.
+  void IgnoreField(const FieldDescriptor* field);
+
+  // Sets the field comparator used to determine differences between protocol
+  // buffer fields. By default it's set to a DefaultFieldComparator instance.
+  // MessageDifferencer doesn't take ownership over the passed object.
+  // Note that this method must be called before Compare for the comparator to
+  // be used.
+  void set_field_comparator(FieldComparator* comparator);
+#ifdef PROTOBUF_FUTURE_BREAKING_CHANGES
+  void set_field_comparator(DefaultFieldComparator* comparator);
+#endif  // PROTOBUF_FUTURE_BREAKING_CHANGES
+
+  // DEPRECATED. Pass a DefaultFieldComparator instance instead.
+  // Sets the fraction and margin for the float comparison of a given field.
+  // Uses MathUtil::WithinFractionOrMargin to compare the values.
+  // NOTE: this method does nothing if differencer's field comparator has been
+  //       set to a custom object.
+  //
+  // REQUIRES: field->cpp_type == FieldDescriptor::CPPTYPE_DOUBLE or
+  //           field->cpp_type == FieldDescriptor::CPPTYPE_FLOAT
+  // REQUIRES: float_comparison_ == APPROXIMATE
+  void SetFractionAndMargin(const FieldDescriptor* field, double fraction,
+                            double margin);
+
+  // Sets the type of comparison (as defined in the MessageFieldComparison
+  // enumeration above) that is used by this differencer when determining how
+  // to compare fields in messages.
+  void set_message_field_comparison(MessageFieldComparison comparison);
+
+  // Returns the current message field comparison used in this differencer.
+  MessageFieldComparison message_field_comparison() const;
+
+  // Tells the differencer whether or not to report matches. This method must
+  // be called before Compare. The default for a new differencer is false.
+  void set_report_matches(bool report_matches) {
+    report_matches_ = report_matches;
+  }
+
+  // Tells the differencer whether or not to report moves (in a set or map
+  // repeated field). This method must be called before Compare. The default for
+  // a new differencer is true.
+  void set_report_moves(bool report_moves) { report_moves_ = report_moves; }
+
+  // Tells the differencer whether or not to report ignored values. This method
+  // must be called before Compare. The default for a new differencer is true.
+  void set_report_ignores(bool report_ignores) {
+    report_ignores_ = report_ignores;
+  }
+
+  // Sets the scope of the comparison (as defined in the Scope enumeration
+  // above) that is used by this differencer when determining which fields to
+  // compare between the messages.
+  void set_scope(Scope scope);
+
+  // Returns the current scope used by this differencer.
+  Scope scope() const;
+
+  // DEPRECATED. Pass a DefaultFieldComparator instance instead.
+  // Sets the type of comparison (as defined in the FloatComparison enumeration
+  // above) that is used by this differencer when comparing float (and double)
+  // fields in messages.
+  // NOTE: this method does nothing if differencer's field comparator has been
+  //       set to a custom object.
+  void set_float_comparison(FloatComparison comparison);
+
+  // Sets the type of comparison for repeated field (as defined in the
+  // RepeatedFieldComparison enumeration above) that is used by this
+  // differencer when compare repeated fields in messages.
+  void set_repeated_field_comparison(RepeatedFieldComparison comparison);
+
+  // Returns the current repeated field comparison used by this differencer.
+  RepeatedFieldComparison repeated_field_comparison() const;
+
+  // Compares the two specified messages, returning true if they are the same,
+  // false otherwise. If this method returns false, any changes between the
+  // two messages will be reported if a Reporter was specified via
+  // ReportDifferencesTo (see also ReportDifferencesToString).
+  //
+  // This method REQUIRES that the two messages have the same
+  // Descriptor (message1.GetDescriptor() == message2.GetDescriptor()).
+  bool Compare(const Message& message1, const Message& message2);
+
+  // Same as above, except comparing only the list of fields specified by the
+  // two vectors of FieldDescriptors.
+  bool CompareWithFields(
+      const Message& message1, const Message& message2,
+      const std::vector<const FieldDescriptor*>& message1_fields,
+      const std::vector<const FieldDescriptor*>& message2_fields);
+
+  // Automatically creates a reporter that will output the differences
+  // found (if any) to the specified output string pointer. Note that this
+  // method must be called before Compare.
+  void ReportDifferencesToString(std::string* output);
+
+  // Tells the MessageDifferencer to report differences via the specified
+  // reporter. Note that this method must be called before Compare for
+  // the reporter to be used. It is the responsibility of the caller to delete
+  // this object.
+  // If the provided pointer equals NULL, the MessageDifferencer stops reporting
+  // differences to any previously set reporters or output strings.
+  void ReportDifferencesTo(Reporter* reporter);
+
+ private:
+  // Class for processing Any deserialization.  This logic is used by both the
+  // MessageDifferencer and StreamReporter classes.
+  class UnpackAnyField {
+   private:
+    std::unique_ptr<DynamicMessageFactory> dynamic_message_factory_;
+
+   public:
+    UnpackAnyField() = default;
+    ~UnpackAnyField() = default;
+    // If "any" is of type google.protobuf.Any, extract its payload using
+    // DynamicMessageFactory and store in "data".
+    bool UnpackAny(const Message& any, std::unique_ptr<Message>* data);
+  };
+
+ public:
+  // An implementation of the MessageDifferencer Reporter that outputs
+  // any differences found in human-readable form to the supplied
+  // ZeroCopyOutputStream or Printer. If a printer is used, the delimiter
+  // *must* be '$'.
+  //
+  // WARNING: this reporter does not necessarily flush its output until it is
+  // destroyed. As a result, it is not safe to assume the output is valid or
+  // complete until after you destroy the reporter. For example, if you use a
+  // StreamReporter to write to a StringOutputStream, the target string may
+  // contain uninitialized data until the reporter is destroyed.
+  class PROTOBUF_EXPORT StreamReporter : public Reporter {
+   public:
+    explicit StreamReporter(io::ZeroCopyOutputStream* output);
+    explicit StreamReporter(io::Printer* printer);  // delimiter '$'
+    ~StreamReporter() override;
+
+    // When set to true, the stream reporter will also output aggregates nodes
+    // (i.e. messages and groups) whose subfields have been modified. When
+    // false, will only report the individual subfields. Defaults to false.
+    void set_report_modified_aggregates(bool report) {
+      report_modified_aggregates_ = report;
+    }
+
+    // The following are implementations of the methods described above.
+
+    void ReportAdded(const Message& message1, const Message& message2,
+                     const std::vector<SpecificField>& field_path) override;
+
+    void ReportDeleted(const Message& message1, const Message& message2,
+                       const std::vector<SpecificField>& field_path) override;
+
+    void ReportModified(const Message& message1, const Message& message2,
+                        const std::vector<SpecificField>& field_path) override;
+
+    void ReportMoved(const Message& message1, const Message& message2,
+                     const std::vector<SpecificField>& field_path) override;
+
+    void ReportMatched(const Message& message1, const Message& message2,
+                       const std::vector<SpecificField>& field_path) override;
+
+    void ReportIgnored(const Message& message1, const Message& message2,
+                       const std::vector<SpecificField>& field_path) override;
+
+    void ReportUnknownFieldIgnored(
+        const Message& message1, const Message& message2,
+        const std::vector<SpecificField>& field_path) override;
+
+    // Messages that are being compared must be provided to StreamReporter prior
+    // to processing
+    void SetMessages(const Message& message1, const Message& message2);
+
+   protected:
+    // Prints the specified path of fields to the buffer.
+    virtual void PrintPath(const std::vector<SpecificField>& field_path,
+                           bool left_side);
+
+    // Prints the value of fields to the buffer.  left_side is true if the
+    // given message is from the left side of the comparison, false if it
+    // was the right.  This is relevant only to decide whether to follow
+    // unknown_field_index1 or unknown_field_index2 when an unknown field
+    // is encountered in field_path.
+    virtual void PrintValue(const Message& message,
+                            const std::vector<SpecificField>& field_path,
+                            bool left_side);
+
+    // Prints the specified path of unknown fields to the buffer.
+    virtual void PrintUnknownFieldValue(const UnknownField* unknown_field);
+
+    // Just print a string
+    void Print(const std::string& str);
+
+   private:
+    // helper function for PrintPath that contains logic for printing maps
+    void PrintMapKey(bool left_side, const SpecificField& specific_field);
+
+    io::Printer* printer_;
+    bool delete_printer_;
+    bool report_modified_aggregates_;
+    const Message* message1_;
+    const Message* message2_;
+    MessageDifferencer::UnpackAnyField unpack_any_field_;
+    GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StreamReporter);
+  };
+
+ private:
+  friend class SimpleFieldComparator;
+
+  // A MapKeyComparator to be used in TreatAsMapUsingKeyComparator.
+  // Implementation of this class needs to do field value comparison which
+  // relies on some private methods of MessageDifferencer. That's why this
+  // class is declared as a nested class of MessageDifferencer.
+  class MultipleFieldsMapKeyComparator;
+
+  // A MapKeyComparator for use with map_entries.
+  class PROTOBUF_EXPORT MapEntryKeyComparator : public MapKeyComparator {
+   public:
+    explicit MapEntryKeyComparator(MessageDifferencer* message_differencer);
+    bool IsMatch(
+        const Message& message1, const Message& message2,
+        const std::vector<SpecificField>& parent_fields) const override;
+
+   private:
+    MessageDifferencer* message_differencer_;
+  };
+
+  // Returns true if field1's number() is less than field2's.
+  static bool FieldBefore(const FieldDescriptor* field1,
+                          const FieldDescriptor* field2);
+
+  // Retrieve all the set fields, including extensions.
+  FieldDescriptorArray RetrieveFields(const Message& message,
+                                      bool base_message);
+
+  // Combine the two lists of fields into the combined_fields output vector.
+  // All fields present in both lists will always be included in the combined
+  // list.  Fields only present in one of the lists will only appear in the
+  // combined list if the corresponding fields_scope option is set to FULL.
+  FieldDescriptorArray CombineFields(const FieldDescriptorArray& fields1,
+                                     Scope fields1_scope,
+                                     const FieldDescriptorArray& fields2,
+                                     Scope fields2_scope);
+
+  // Internal version of the Compare method which performs the actual
+  // comparison. The parent_fields vector is a vector containing field
+  // descriptors of all fields accessed to get to this comparison operation
+  // (i.e. if the current message is an embedded message, the parent_fields
+  // vector will contain the field that has this embedded message).
+  bool Compare(const Message& message1, const Message& message2,
+               std::vector<SpecificField>* parent_fields);
+
+  // Compares all the unknown fields in two messages.
+  bool CompareUnknownFields(const Message& message1, const Message& message2,
+                            const UnknownFieldSet&, const UnknownFieldSet&,
+                            std::vector<SpecificField>* parent_fields);
+
+  // Compares the specified messages for the requested field lists. The field
+  // lists are modified depending on comparison settings, and then passed to
+  // CompareWithFieldsInternal.
+  bool CompareRequestedFieldsUsingSettings(
+      const Message& message1, const Message& message2,
+      const FieldDescriptorArray& message1_fields,
+      const FieldDescriptorArray& message2_fields,
+      std::vector<SpecificField>* parent_fields);
+
+  // Compares the specified messages with the specified field lists.
+  bool CompareWithFieldsInternal(const Message& message1,
+                                 const Message& message2,
+                                 const FieldDescriptorArray& message1_fields,
+                                 const FieldDescriptorArray& message2_fields,
+                                 std::vector<SpecificField>* parent_fields);
+
+  // Compares the repeated fields, and report the error.
+  bool CompareRepeatedField(const Message& message1, const Message& message2,
+                            const FieldDescriptor* field,
+                            std::vector<SpecificField>* parent_fields);
+
+  // Compares map fields, and report the error.
+  bool CompareMapField(const Message& message1, const Message& message2,
+                       const FieldDescriptor* field,
+                       std::vector<SpecificField>* parent_fields);
+
+  // Helper for CompareRepeatedField and CompareMapField: compares and reports
+  // differences element-wise. This is the implementation for non-map fields,
+  // and can also compare map fields by using the underlying representation.
+  bool CompareRepeatedRep(const Message& message1, const Message& message2,
+                          const FieldDescriptor* field,
+                          std::vector<SpecificField>* parent_fields);
+
+  // Helper for CompareMapField: compare the map fields using map reflection
+  // instead of sync to repeated.
+  bool CompareMapFieldByMapReflection(const Message& message1,
+                                      const Message& message2,
+                                      const FieldDescriptor* field,
+                                      std::vector<SpecificField>* parent_fields,
+                                      DefaultFieldComparator* comparator);
+
+  // Shorthand for CompareFieldValueUsingParentFields with NULL parent_fields.
+  bool CompareFieldValue(const Message& message1, const Message& message2,
+                         const FieldDescriptor* field, int index1, int index2);
+
+  // Compares the specified field on the two messages, returning
+  // true if they are the same, false otherwise. For repeated fields,
+  // this method only compares the value in the specified index. This method
+  // uses Compare functions to recurse into submessages.
+  // The parent_fields vector is used in calls to a Reporter instance calls.
+  // It can be NULL, in which case the MessageDifferencer will create new
+  // list of parent messages if it needs to recursively compare the given field.
+  // To avoid confusing users you should not set it to NULL unless you modified
+  // Reporter to handle the change of parent_fields correctly.
+  bool CompareFieldValueUsingParentFields(
+      const Message& message1, const Message& message2,
+      const FieldDescriptor* field, int index1, int index2,
+      std::vector<SpecificField>* parent_fields);
+
+  // Compares the specified field on the two messages, returning comparison
+  // result, as returned by appropriate FieldComparator.
+  FieldComparator::ComparisonResult GetFieldComparisonResult(
+      const Message& message1, const Message& message2,
+      const FieldDescriptor* field, int index1, int index2,
+      const FieldContext* field_context);
+
+  // Check if the two elements in the repeated field are match to each other.
+  // if the key_comprator is NULL, this function returns true when the two
+  // elements are equal.
+  bool IsMatch(const FieldDescriptor* repeated_field,
+               const MapKeyComparator* key_comparator, const Message* message1,
+               const Message* message2,
+               const std::vector<SpecificField>& parent_fields,
+               Reporter* reporter, int index1, int index2);
+
+  // Returns true when this repeated field has been configured to be treated
+  // as a Set / SmartSet / SmartList.
+  bool IsTreatedAsSet(const FieldDescriptor* field);
+  bool IsTreatedAsSmartSet(const FieldDescriptor* field);
+
+  bool IsTreatedAsSmartList(const FieldDescriptor* field);
+  // When treating as SMART_LIST, it uses MatchIndicesPostProcessorForSmartList
+  // by default to find the longest matching sequence from the first matching
+  // element. The callback takes two vectors showing the matching indices from
+  // the other vector, where -1 means an unmatch.
+  void SetMatchIndicesForSmartListCallback(
+      std::function<void(std::vector<int>*, std::vector<int>*)> callback);
+
+  // Returns true when this repeated field is to be compared as a subset, ie.
+  // has been configured to be treated as a set or map and scope is set to
+  // PARTIAL.
+  bool IsTreatedAsSubset(const FieldDescriptor* field);
+
+  // Returns true if this field is to be ignored when this
+  // MessageDifferencer compares messages.
+  bool IsIgnored(const Message& message1, const Message& message2,
+                 const FieldDescriptor* field,
+                 const std::vector<SpecificField>& parent_fields);
+
+  // Returns true if this unknown field is to be ignored when this
+  // MessageDifferencer compares messages.
+  bool IsUnknownFieldIgnored(const Message& message1, const Message& message2,
+                             const SpecificField& field,
+                             const std::vector<SpecificField>& parent_fields);
+
+  // Returns MapKeyComparator* when this field has been configured to be treated
+  // as a map or its is_map() return true.  If not, returns NULL.
+  const MapKeyComparator* GetMapKeyComparator(
+      const FieldDescriptor* field) const;
+
+  // Attempts to match indices of a repeated field, so that the contained values
+  // match. Clears output vectors and sets their values to indices of paired
+  // messages, ie. if message1[0] matches message2[1], then match_list1[0] == 1
+  // and match_list2[1] == 0. The unmatched indices are indicated by -1.
+  // Assumes the repeated field is not treated as a simple list.
+  // This method returns false if the match failed. However, it doesn't mean
+  // that the comparison succeeds when this method returns true (you need to
+  // double-check in this case).
+  bool MatchRepeatedFieldIndices(
+      const Message& message1, const Message& message2,
+      const FieldDescriptor* repeated_field,
+      const MapKeyComparator* key_comparator,
+      const std::vector<SpecificField>& parent_fields,
+      std::vector<int>* match_list1, std::vector<int>* match_list2);
+
+  // Checks if index is equal to new_index in all the specific fields.
+  static bool CheckPathChanged(const std::vector<SpecificField>& parent_fields);
+
+  // CHECKs that the given repeated field can be compared according to
+  // new_comparison.
+  void CheckRepeatedFieldComparisons(
+      const FieldDescriptor* field,
+      const RepeatedFieldComparison& new_comparison);
+
+  // Defines a map between field descriptors and their MapKeyComparators.
+  // Used for repeated fields when they are configured as TreatAsMap.
+  typedef std::map<const FieldDescriptor*, const MapKeyComparator*>
+      FieldKeyComparatorMap;
+
+  // Defines a set to store field descriptors.  Used for repeated fields when
+  // they are configured as TreatAsSet.
+  typedef std::set<const FieldDescriptor*> FieldSet;
+  typedef std::map<const FieldDescriptor*, RepeatedFieldComparison> FieldMap;
+
+  Reporter* reporter_;
+  DefaultFieldComparator default_field_comparator_;
+  MessageFieldComparison message_field_comparison_;
+  Scope scope_;
+  RepeatedFieldComparison repeated_field_comparison_;
+
+  FieldMap repeated_field_comparisons_;
+  // Keeps track of MapKeyComparators that are created within
+  // MessageDifferencer. These MapKeyComparators should be deleted
+  // before MessageDifferencer is destroyed.
+  // When TreatAsMap or TreatAsMapWithMultipleFieldsAsKey is called, we don't
+  // store the supplied FieldDescriptors directly. Instead, a new
+  // MapKeyComparator is created for comparison purpose.
+  std::vector<MapKeyComparator*> owned_key_comparators_;
+  FieldKeyComparatorMap map_field_key_comparator_;
+  MapEntryKeyComparator map_entry_key_comparator_;
+  std::vector<IgnoreCriteria*> ignore_criteria_;
+  // Reused multiple times in RetrieveFields to avoid extra allocations
+  std::vector<const FieldDescriptor*> tmp_message_fields_;
+
+  FieldSet ignored_fields_;
+
+  union {
+    DefaultFieldComparator* default_impl;
+    FieldComparator* base;
+  } field_comparator_ = {&default_field_comparator_};
+  enum { kFCDefault, kFCBase } field_comparator_kind_ = kFCDefault;
+
+  bool report_matches_;
+  bool report_moves_;
+  bool report_ignores_;
+
+  std::string* output_string_;
+
+  // Callback to post-process the matched indices to support SMART_LIST.
+  std::function<void(std::vector<int>*, std::vector<int>*)>
+      match_indices_for_smart_list_callback_;
+
+  MessageDifferencer::UnpackAnyField unpack_any_field_;
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MessageDifferencer);
+};
+
+// This class provides extra information to the FieldComparator::Compare
+// function.
+class PROTOBUF_EXPORT FieldContext {
+ public:
+  explicit FieldContext(
+      std::vector<MessageDifferencer::SpecificField>* parent_fields)
+      : parent_fields_(parent_fields) {}
+
+  std::vector<MessageDifferencer::SpecificField>* parent_fields() const {
+    return parent_fields_;
+  }
+
+ private:
+  std::vector<MessageDifferencer::SpecificField>* parent_fields_;
+};
+
+}  // namespace util
+}  // namespace protobuf
+}  // namespace google
+
+#include <google/protobuf/port_undef.inc>
+
+#endif  // GOOGLE_PROTOBUF_UTIL_MESSAGE_DIFFERENCER_H__