Fix hydrodynamics deprecation warning. (#2579)

The warning message in the hydrodynamics added mass section is broken.
Firstly, we probably should check for if any value was set on the added
mass. Secondly, the message was mangled. Finally we downgraded the error
to a warning as the error leads to users getting confused.

Signed-off-by: Arjo Chakravarty <[email protected]>

src/systems/hydrodynamics/Hydrodynamics.cc

@@ -355,21 +355,22 @@ void Hydrodynamics::Configure(
       prefix += snameConventionVel[j];
       this->dataPtr->Ma(i, j) = SdfParamDouble(_sdf, prefix, 0);
       addedMassSpecified = (std::abs(this->dataPtr->Ma(i, j)) > 1e-6)
-      && addedMassSpecified;
+        || addedMassSpecified;
     }
   }
 
   _sdf->Get<bool>("disable_coriolis", this->dataPtr->disableCoriolis, false);
-  _sdf->Get<bool>("disable_added_mass", this->dataPtr->disableAddedMass, false);
-  if (!this->dataPtr->disableAddedMass || addedMassSpecified)
+  _sdf->Get<bool>("disable_added_mass",
+    this->dataPtr->disableAddedMass, false);
+  if (!this->dataPtr->disableAddedMass && addedMassSpecified)
   {
-    gzerr << "The use of added mass through this plugin is deprecated and will"
-      << "be removed in Gazebo J* as this formulation has instabilities."
-      << " We recommend using the SDF `<fluid_added_mass>` tag based method"
+    gzwarn << "The use of added mass through this plugin is deprecated and "
+      << "will be removed in Gazebo J* as this formulation has instabilities. "
+      << "We recommend using the SDF `<fluid_added_mass>` tag based method "
       << "[http://sdformat.org/spec?ver=1.11&elem=link"
       << "#inertial_fluid_added_mass]"
-      << "To get rid of this warning we recommend setting"
-      << "`<disable_added_mass> to true."
+      << "To get rid of this warning we recommend setting "
+      << "`<disable_added_mass>` to true and updating your model"
       << std::endl;
   }
   // Create model object, to access convenient functions