Restore support for non-qualified message names

Migration.md

@@ -35,11 +35,6 @@ release will remove the deprecated code.
   const msgs::SphericalCoordinatesType &_sc)`
       does not accept `msgs::SphericalCoordinatesType::LOCAL2` anymore.
 
-1. **MessageFactory.hh**
-    + The function `MessageFactory::MessagePtr MessageFactory::New(
-    const std::string &_msgType)` does not accept non-fully qualified names
-    anymore.
-
 ## Gazebo Msgs 10.X to 11.X
 ### Deprecations
 

core/src/MessageFactory.cc

@@ -94,6 +94,21 @@ MessageFactory::MessagePtr MessageFactory::New(
   };
 
   auto ret = getMessagePtr(type);
+
+  // Message was not found in either static or dynamic message types,
+  // try again adding the gz.msgs prefix
+  if (nullptr == ret)
+  {
+    ret = getMessagePtr(kGzMsgsPrefix + type);
+    if (nullptr != ret)
+    {
+      // Do not remove this until support is added to gz-transport:
+      // https://github.com/gazebosim/gz-transport/issues/435
+      std::cerr << "Message (" << kGzMsgsPrefix + type
+          << ") was retrieved with non-fully qualified name. "
+          << "This behavior is deprecated in msgs12" << std::endl;
+    }
+  }
   return ret;
 }
 

test/integration/Factory_TEST.cc

@@ -100,7 +100,7 @@ TEST(FactoryTest, NewWithMalformedData)
 TEST(FactoryTest, DeprecatedNonFullyQualified)
 {
   auto msg = Factory::New("StringMsg");
-  EXPECT_TRUE(msg.get() == nullptr);
+  EXPECT_TRUE(msg.get() != nullptr);
 }
 
 /////////////////////////////////////////////////