sim/sim_model: fix an annoying issue when adding new fields: their ID was

set in undefined, that create an issue (the canonical name was returned as
"Field-1", breaking the schematic file).
Now, new field IDs are not set to -1, and the saved file uses the field name
(if exist) when saving fields with undefined ID.

eeschema/sch_plugins/kicad/sch_sexpr_plugin.cpp

@@ -873,6 +873,11 @@ void SCH_SEXPR_PLUGIN::saveField( SCH_FIELD* aField, int aNestLevel )
 
     if( aField->GetId() == -1 /* undefined ID */ )
     {
+        // Replace the default name built by GetCanonicalName() by
+        // the field name if exists
+        if( !aField->GetName().IsEmpty() )
+            fieldName = aField->GetName();
+
         aField->SetId( m_nextFreeFieldId );
         m_nextFreeFieldId += 1;
     }

eeschema/sim/sim_model.cpp

@@ -1051,6 +1051,24 @@ void SIM_MODEL::doReadDataFields( const std::vector<T>* aFields,
 template <typename T>
 void SIM_MODEL::doWriteFields( std::vector<T>& aFields ) const
 {
+    // Remove duplicate fields: they are at the end of list
+    for( size_t ii = aFields.size() - 1; ii > 0; ii-- )
+    {
+        wxString currFieldName = aFields[ii].GetName();
+
+        auto end_candidate_list = aFields.begin() + ii - 1;
+
+        auto fieldIt = std::find_if( aFields.begin(), end_candidate_list,
+                                     [&]( const T& f )
+                                     {
+                                        return f.GetName() == currFieldName;
+                                     } );
+
+        // If duplicate field found: remove current checked item
+        if( fieldIt != end_candidate_list )
+            aFields.erase( aFields.begin() + ii );
+    }
+
     SetFieldValue( aFields, SIM_DEVICE_TYPE_FIELD, m_serializer->GenerateDevice() );
     SetFieldValue( aFields, SIM_TYPE_FIELD, m_serializer->GenerateType() );
 
@@ -1061,6 +1079,24 @@ void SIM_MODEL::doWriteFields( std::vector<T>& aFields ) const
 
     if( IsStoredInValue() )
         SetFieldValue( aFields, SIM_VALUE_FIELD, m_serializer->GenerateValue() );
+
+    // New fields have a ID = -1 (undefined). so replace the undefined ID
+    // by a degined ID
+    int lastFreeId = MANDATORY_FIELDS;
+
+    // Search for the first available value:
+    for( auto& fld : aFields )
+    {
+        if( fld.GetId() >= lastFreeId )
+            lastFreeId = fld.GetId() + 1;
+    }
+
+    // Set undefined IDs to a better value
+    for( auto& fld : aFields )
+    {
+        if( fld.GetId() < 0 )
+            fld.SetId( lastFreeId++ );
+    }
 }