Make sure to quality calls to std::swap.  Otherwise, if a google::swap() exists (e.g. because the user is using our own dense_hash_map implementation) it will be chosen instead, leading to a compile error.

src/google/protobuf/compiler/command_line_interface_unittest.cc

diff --git a/src/google/protobuf/compiler/command_line_interface_unittest.cc b/src/google/protobuf/compiler/command_line_interface_unittest.cc
index 719771e..0784e78 100644
--- a/src/google/protobuf/compiler/command_line_interface_unittest.cc
+++ b/src/google/protobuf/compiler/command_line_interface_unittest.cc
@@ -775,8 +775,8 @@
   if (HasFatalFailure()) return;
   ASSERT_EQ(2, descriptor_set.file_size());
   if (descriptor_set.file(0).name() == "bar.proto") {
-    swap(descriptor_set.mutable_file()->mutable_data()[0],
-         descriptor_set.mutable_file()->mutable_data()[1]);
+    std::swap(descriptor_set.mutable_file()->mutable_data()[0],
+              descriptor_set.mutable_file()->mutable_data()[1]);
   }
   EXPECT_EQ("foo.proto", descriptor_set.file(0).name());
   EXPECT_EQ("bar.proto", descriptor_set.file(1).name());

src/google/protobuf/generated_message_reflection.cc

diff --git a/src/google/protobuf/generated_message_reflection.cc b/src/google/protobuf/generated_message_reflection.cc
index d294e58..e04b93c 100644
--- a/src/google/protobuf/generated_message_reflection.cc
+++ b/src/google/protobuf/generated_message_reflection.cc
@@ -324,7 +324,7 @@
   int has_bits_size = (descriptor_->field_count() + 31) / 32;
 
   for (int i = 0; i < has_bits_size; i++) {
-    swap(has_bits1[i], has_bits2[i]);
+    std::swap(has_bits1[i], has_bits2[i]);
   }
 
   for (int i = 0; i < descriptor_->field_count(); i++) {
@@ -360,8 +360,8 @@
       switch (field->cpp_type()) {
 #define SWAP_VALUES(CPPTYPE, TYPE)                                           \
         case FieldDescriptor::CPPTYPE_##CPPTYPE:                             \
-          swap(*MutableRaw<TYPE>(message1, field),                           \
-               *MutableRaw<TYPE>(message2, field));                          \
+          std::swap(*MutableRaw<TYPE>(message1, field),                      \
+                    *MutableRaw<TYPE>(message2, field));                     \
           break;
 
           SWAP_VALUES(INT32 , int32 );
@@ -376,8 +376,8 @@
 #undef SWAP_VALUES
 
         case FieldDescriptor::CPPTYPE_STRING:
-            swap(*MutableRaw<string*>(message1, field),
-                 *MutableRaw<string*>(message2, field));
+            std::swap(*MutableRaw<string*>(message1, field),
+                      *MutableRaw<string*>(message2, field));
           break;
 
         default:

src/google/protobuf/repeated_field.h

diff --git a/src/google/protobuf/repeated_field.h b/src/google/protobuf/repeated_field.h
index 43c9f3f..1696e2a 100644
--- a/src/google/protobuf/repeated_field.h
+++ b/src/google/protobuf/repeated_field.h
@@ -491,7 +491,7 @@
 
 template <typename Element>
 void RepeatedField<Element>::SwapElements(int index1, int index2) {
-  swap(elements_[index1], elements_[index2]);
+  std::swap(elements_[index1], elements_[index2]);
 }
 
 template <typename Element>
@@ -627,7 +627,7 @@
 }
 
 inline void RepeatedPtrFieldBase::SwapElements(int index1, int index2) {
-  swap(elements_[index1], elements_[index2]);
+  std::swap(elements_[index1], elements_[index2]);
 }
 
 template <typename TypeHandler>