Export comma-delimited values instead of "-- mixed values --".

Fixes https://gitlab.com/kicad/code/kicad/-/issues/17912

eeschema/fields_data_model.cpp

@@ -173,9 +173,11 @@ wxString FIELDS_EDITOR_GRID_DATA_MODEL::GetValue( int aRow, int aCol )
 wxString FIELDS_EDITOR_GRID_DATA_MODEL::GetValue( const DATA_MODEL_ROW& group, int aCol,
                                                   const wxString& refDelimiter,
                                                   const wxString& refRangeDelimiter,
-                                                  bool            resolveVars )
+                                                  bool            resolveVars,
+                                                  bool            listMixedValues )
 {
     std::vector<SCH_REFERENCE> references;
+    std::set<wxString>         mixedValues;
     wxString                   fieldValue;
 
     for( const SCH_REFERENCE& ref : group.m_Refs )
@@ -209,13 +211,30 @@ wxString FIELDS_EDITOR_GRID_DATA_MODEL::GetValue( const DATA_MODEL_ROW& group, i
                 refFieldValue = m_dataStore[symbolID][m_cols[aCol].m_fieldName];
             }
 
-            if( &ref == &group.m_Refs.front() )
+            if( listMixedValues )
+                mixedValues.insert( refFieldValue );
+            else if( &ref == &group.m_Refs.front() )
                 fieldValue = refFieldValue;
             else if( fieldValue != refFieldValue )
                 return INDETERMINATE_STATE;
         }
     }
 
+    if( listMixedValues && mixedValues.size() > 1 )
+    {
+        fieldValue = wxEmptyString;
+
+        for( const wxString& value : mixedValues )
+        {
+            if( value.IsEmpty() )
+                continue;
+            else if( fieldValue.IsEmpty() )
+                fieldValue = value;
+            else
+                fieldValue += "," + value;
+        }
+    }
+
     if( ColIsReference( aCol ) || ColIsQuantity( aCol ) || ColIsItemNumber( aCol ) )
     {
         // Remove duplicates (other units of multi-unit parts)

eeschema/fields_data_model.h

@@ -157,12 +157,13 @@ public:
     wxString GetValue( const DATA_MODEL_ROW& group, int aCol,
                        const wxString& refDelimiter = wxT( ", " ),
                        const wxString& refRangDelimiter = wxT( "-" ),
-                       bool resolveVars = false );
+                       bool resolveVars = false,
+                       bool listMixedValues = false );
 
     wxString GetExportValue( int aRow, int aCol, const wxString& refDelimiter,
                              const wxString& refRangeDelimiter )
     {
-        return GetValue( m_rows[aRow], aCol, refDelimiter, refRangeDelimiter, true );
+        return GetValue( m_rows[aRow], aCol, refDelimiter, refRangeDelimiter, true, true );
     }
 
     void     SetValue( int aRow, int aCol, const wxString& aValue ) override;