Load always the own gz_msgs*.gz_desc first and avoid duplicates

core/src/DynamicFactory.cc

@@ -27,6 +27,7 @@
 #include "DynamicFactory.hh"
 #include "gz/utils/Environment.hh"
 
+#include <gz/msgs/config.hh>
 #include <gz/msgs/InstallationDirectories.hh>
 
 namespace {
@@ -121,6 +122,13 @@ void DynamicFactory::LoadDescriptors(const std::string &_paths)
     for (const google::protobuf::FileDescriptorProto &fileDescriptorProto :
          fileDescriptorSet.file())
     {
+      // Skip protos already loaded (e.g. same .gz_desc reached via
+      // both GZ_DESCRIPTOR_PATH and the global share directory).
+      if (this->pool.FindFileByName(fileDescriptorProto.name()) != nullptr)
+      {
+        continue;
+      }
+
       if (!static_cast<bool>(this->pool.BuildFile(fileDescriptorProto)))
       {
         std::cerr << "DynamicFactory(). Unable to place descriptors from ["
@@ -133,6 +141,9 @@ void DynamicFactory::LoadDescriptors(const std::string &_paths)
     }
   };
 
+  const std::string ownDescFile =
+    "gz-msgs" + std::to_string(GZ_MSGS_MAJOR_VERSION) + ".gz_desc";
+
   for (const std::string &descDir : descDirs)
   {
     if (!std::filesystem::is_directory(descDir))
@@ -141,8 +152,18 @@ void DynamicFactory::LoadDescriptors(const std::string &_paths)
     }
     else
     {
+      // Default to loading the descriptor file for this gz-msgs major version if it exists
+      auto ownDescPath = std::filesystem::path(descDir) / ownDescFile;
+      if (std::filesystem::exists(ownDescPath))
+      {
+        loadDescFile(ownDescPath.string());
+      }
+
       for (auto const &dirIter : std::filesystem::directory_iterator{descDir})
       {
+        auto filename = dirIter.path().filename().string();
+        if (filename == ownDescFile)  // Skip the ownDesc already loaded
+          continue;
         loadDescFile(dirIter.path().string());
       }
     }

test/integration/descriptors.cc

@@ -93,3 +93,38 @@ TEST(FactoryTest, DynamicFactory)
   EXPECT_NE(nullptr, gz::msgs::Factory::New("testing.BarMessage"));
   EXPECT_NE(nullptr, gz::msgs::Factory::New("testing.BazMessage"));
 }
+
+TEST(FactoryTest, NoDuplicateDescriptors)
+{
+  // Regression test for https://github.com/gazebosim/gz-msgs/issues/460
+  // When the same .gz_desc file is reachable via both GZ_DESCRIPTOR_PATH
+  // and the global share directory, the DynamicFactory used to print:
+  //   [libprotobuf ERROR] File already exists in database: ...
+  // The fix silently skips proto definitions already present in the pool.
+
+  std::filesystem::path test_path(kMsgsTestPath);
+  std::string path = (test_path / "desc" / "stringmsg.desc").string();
+
+#ifdef _WIN32
+  std::string paths = path + ";" + path;
+#else
+  std::string paths = path + ":" + path;
+#endif
+
+  // Capture stderr to detect any "already exists in database" errors from
+  // libprotobuf.  Using gtest's CaptureStderr avoids depending on the
+  // protobuf-internal SetLogHandler API, which was removed in protobuf 4.x.
+  ::testing::internal::CaptureStderr();
+
+  // Loading the same descriptor twice must not cause protobuf errors.
+  // The second occurrence is skipped because the protos are already in the pool.
+  gz::msgs::Factory::LoadDescriptors(paths);
+
+  std::string stderr_output = ::testing::internal::GetCapturedStderr();
+  EXPECT_EQ(stderr_output.find("already exists in database"), std::string::npos)
+    << "libprotobuf ERROR emitted during duplicate descriptor load: "
+    << stderr_output;
+
+  // The message type must remain accessible after duplicate loading.
+  EXPECT_NE(nullptr, gz::msgs::Factory::New("example.msgs.StringMsg"));
+}