Fix dbus::Property compile failure on gcc

dbus/property.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef DBUS_PROPERTY_H_
 #define DBUS_PROPERTY_H_
 
 #include <map>
 #include <string>
 
@@ skipping 388 matching lines @@
   }
 
  private:
   // Current cached value of the property.
   T value_;
 
   // Replacement value of the property.
   T set_value_;
 };
 
 template <> Property<uint8>::Property();

[Nico, 2014/07/25 16:46:50]

…and this line is wrong too I think. Since the constructor is defined inline
above, you shouldn't instantiate it here, that'll lead to an instantiation of
the template, not to a specialization.

So I recommend:
* Remove all the ::Property() lines
* For consistency with other code, remove the CHROME_DBUS_EXPORT from the extern
template class liens

[tzik, 2014/07/29 05:52:36]

These Property::Property()s seem specialization rather than instantiation.
property.cc provides slightly different implementation for them.

We can implement them uniformly like below, which is common way in Chromium:
Property() : value_(), set_value_() {}

 template <> bool Property<uint8>::PopValueFromReader(MessageReader* reader);
 template <> void Property<uint8>::AppendSetValueToWriter(MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<uint8>;

[Nico, 2014/07/25 16:37:23]

Just removing the CHROME_DBUS_EXPORT should be enough to fix that error, no?

[tzik, 2014/07/29 05:52:36]

That doesn't build successfully on clang+asan on latest clang, unfortunately.
The error message was same as the first try of the fix:
https://codereview.chromium.org/354553002#msg1

 
 template <> Property<bool>::Property();
 template <> bool Property<bool>::PopValueFromReader(MessageReader* reader);
 template <> void Property<bool>::AppendSetValueToWriter(MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<bool>;
 
 template <> Property<int16>::Property();
 template <> bool Property<int16>::PopValueFromReader(MessageReader* reader);
 template <> void Property<int16>::AppendSetValueToWriter(MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<int16>;
 
 template <> Property<uint16>::Property();
 template <> bool Property<uint16>::PopValueFromReader(MessageReader* reader);
 template <> void Property<uint16>::AppendSetValueToWriter(
   MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<uint16>;
 
 template <> Property<int32>::Property();
 template <> bool Property<int32>::PopValueFromReader(MessageReader* reader);
 template <> void Property<int32>::AppendSetValueToWriter(MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<int32>;
 
 template <> Property<uint32>::Property();
 template <> bool Property<uint32>::PopValueFromReader(MessageReader* reader);
 template <> void Property<uint32>::AppendSetValueToWriter(
   MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<uint32>;
 
 template <> Property<int64>::Property();
 template <> bool Property<int64>::PopValueFromReader(MessageReader* reader);
 template <> void Property<int64>::AppendSetValueToWriter(MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<int64>;
 
 template <> Property<uint64>::Property();
 template <> bool Property<uint64>::PopValueFromReader(MessageReader* reader);
 template <> void Property<uint64>::AppendSetValueToWriter(
   MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<uint64>;
 
 template <> Property<double>::Property();
 template <> bool Property<double>::PopValueFromReader(MessageReader* reader);
 template <> void Property<double>::AppendSetValueToWriter(
   MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<double>;
 
 template <> bool Property<std::string>::PopValueFromReader(
   MessageReader* reader);
 template <> void Property<std::string>::AppendSetValueToWriter(
   MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<std::string>;
 
 template <> bool Property<ObjectPath>::PopValueFromReader(
   MessageReader* reader);
 template <> void Property<ObjectPath>::AppendSetValueToWriter(
   MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<ObjectPath>;
 
 template <> bool Property<std::vector<std::string> >::PopValueFromReader(
   MessageReader* reader);
 template <> void Property<std::vector<std::string> >::AppendSetValueToWriter(
   MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<std::vector<std::string> >;
 
 template <> bool Property<std::vector<ObjectPath> >::PopValueFromReader(
   MessageReader* reader);
 template <> void Property<std::vector<ObjectPath> >::AppendSetValueToWriter(
   MessageWriter* writer);
-extern template class CHROME_DBUS_EXPORT Property<std::vector<ObjectPath> >;
 
 template <> bool Property<std::vector<uint8> >::PopValueFromReader(
   MessageReader* reader);
 template <> void Property<std::vector<uint8> >::AppendSetValueToWriter(
   MessageWriter* writer);
+
+#if defined(COMPILER_GCC) && !defined(__clang__)
+extern template class Property<uint8>;
+extern template class Property<bool>;
+extern template class Property<int16>;
+extern template class Property<uint16>;
+extern template class Property<int32>;
+extern template class Property<uint32>;
+extern template class Property<int64>;
+extern template class Property<uint64>;
+extern template class Property<double>;
+extern template class Property<std::string>;
+extern template class Property<ObjectPath>;
+extern template class Property<std::vector<std::string> >;
+extern template class Property<std::vector<ObjectPath> >;
+extern template class Property<std::vector<uint8> >;
+#else
+extern template class CHROME_DBUS_EXPORT Property<uint8>;
+extern template class CHROME_DBUS_EXPORT Property<bool>;
+extern template class CHROME_DBUS_EXPORT Property<int16>;
+extern template class CHROME_DBUS_EXPORT Property<uint16>;
+extern template class CHROME_DBUS_EXPORT Property<int32>;
+extern template class CHROME_DBUS_EXPORT Property<uint32>;
+extern template class CHROME_DBUS_EXPORT Property<int64>;
+extern template class CHROME_DBUS_EXPORT Property<uint64>;
+extern template class CHROME_DBUS_EXPORT Property<double>;
+extern template class CHROME_DBUS_EXPORT Property<std::string>;
+extern template class CHROME_DBUS_EXPORT Property<ObjectPath>;
+extern template class CHROME_DBUS_EXPORT Property<std::vector<std::string> >;
+extern template class CHROME_DBUS_EXPORT Property<std::vector<ObjectPath> >;
 extern template class CHROME_DBUS_EXPORT Property<std::vector<uint8> >;
+#endif
 
 }  // namespace dbus
 
 #endif  // DBUS_PROPERTY_H_