m_ordinal has no meaning for mandatory fields.

... but it should still be initialised.

eeschema/lib_symbol.h

@@ -404,8 +404,6 @@ public:
 
     void RemoveField( SCH_FIELD* aField ) { RemoveDrawItem( aField ); }
 
-    size_t GetFieldCount() const { return m_drawings.size( SCH_FIELD_T ); }
-
     /**
      * Return a list of pin object pointers from the draw item list.
      *

eeschema/sch_field.cpp

@@ -48,6 +48,7 @@ SCH_FIELD::SCH_FIELD() :
         SCH_ITEM( nullptr, SCH_FIELD_T ),
         EDA_TEXT( schIUScale, wxEmptyString ),
         m_id( FIELD_T::USER ),
+        m_ordinal( 0 ),
         m_showName( false ),
         m_allowAutoPlace( true ),
         m_isNamedVariable( false ),
@@ -79,6 +80,15 @@ SCH_FIELD::SCH_FIELD( const VECTOR2I& aPos, FIELD_T aFieldId, SCH_ITEM* aParent,
 SCH_FIELD::SCH_FIELD( SCH_ITEM* aParent, FIELD_T aFieldId, const wxString& aName ) :
         SCH_FIELD( VECTOR2I(), aFieldId, aParent, aName )
 {
+    if( aFieldId == FIELD_T::USER && aParent )
+    {
+        if( aParent->Type() == SCH_SYMBOL_T )
+            m_ordinal = static_cast<SCH_SYMBOL*>( aParent )->GetNextFieldOrdinal();
+        else if( aParent->Type() == SCH_SHEET_T )
+            m_ordinal = static_cast<SCH_SHEET*>( aParent )->GetNextFieldOrdinal();
+        else if( SCH_LABEL_BASE* label = dynamic_cast<SCH_LABEL_BASE*>( aParent ) )
+            m_ordinal = label->GetNextFieldOrdinal();
+    }
 }
 
 
@@ -1372,9 +1382,20 @@ bool SCH_FIELD::operator==( const SCH_FIELD& aOther ) const
         return false;
     }
 
-    if( GetId() != aOther.GetId() )
+    if( IsMandatory() != aOther.IsMandatory() )
         return false;
 
+    if( IsMandatory() )
+    {
+        if( GetId() != aOther.GetId() )
+            return false;
+    }
+    else
+    {
+        if( GetOrdinal() != aOther.GetOrdinal() )
+            return false;
+    }
+
     if( GetPosition() != aOther.GetPosition() )
         return false;
 

eeschema/sch_field.h

@@ -353,6 +353,17 @@ private:
 };
 
 
+inline int NextFieldOrdinal( const std::vector<SCH_FIELD>& aFields )
+{
+    int ordinal = 42;     // Arbitrarily larger than any mandatory FIELD_T id
+
+    for( const SCH_FIELD& field : aFields )
+        ordinal = std::max( ordinal, field.GetOrdinal() + 1 );
+
+    return ordinal;
+}
+
+
 inline const SCH_FIELD* FindField( const std::vector<SCH_FIELD>& aFields, FIELD_T aFieldId )
 {
     for( const SCH_FIELD& field : aFields )

eeschema/sch_label.cpp

@@ -212,6 +212,12 @@ const wxString SCH_LABEL_BASE::GetDefaultFieldName( const wxString& aName, bool
 }
 
 
+int SCH_LABEL_BASE::GetNextFieldOrdinal() const
+{
+    return NextFieldOrdinal( m_fields );
+}
+
+
 bool SCH_LABEL_BASE::IsType( const std::vector<KICAD_T>& aScanTypes ) const
 {
     static const std::vector<KICAD_T> wireAndPinTypes = { SCH_ITEM_LOCATE_WIRE_T, SCH_PIN_T };

eeschema/sch_label.h

@@ -197,6 +197,11 @@ public:
 
     static const wxString GetDefaultFieldName( const wxString& aName, bool aUseDefaultName );
 
+    /**
+     * Return the next ordinal for a user field for this label
+     */
+    int GetNextFieldOrdinal() const;
+
     virtual int GetMandatoryFieldCount()              { return 0; }
 
     std::vector<SCH_FIELD>& GetFields()               { return m_fields; }

eeschema/sch_sheet.cpp

@@ -386,6 +386,12 @@ const SCH_FIELD* SCH_SHEET::GetField( FIELD_T aFieldType ) const
 }
 
 
+int SCH_SHEET::GetNextFieldOrdinal() const
+{
+    return NextFieldOrdinal( m_fields );
+}
+
+
 void SCH_SHEET::SetFields( const std::vector<SCH_FIELD>& aFields )
 {
     m_fields = aFields;

eeschema/sch_sheet.h

@@ -94,6 +94,11 @@ public:
     SCH_FIELD* GetField( FIELD_T aFieldType );
     const SCH_FIELD* GetField( FIELD_T aFieldNdx ) const;
 
+    /**
+     * Return the next ordinal for a user field for this sheet
+     */
+    int GetNextFieldOrdinal() const;
+
     /**
      * Set multiple schematic fields.
      *

eeschema/sch_symbol.cpp

@@ -859,6 +859,12 @@ void SCH_SYMBOL::GetFields( std::vector<SCH_FIELD*>& aVector, bool aVisibleOnly
 }
 
 
+int SCH_SYMBOL::GetNextFieldOrdinal() const
+{
+    return NextFieldOrdinal( m_fields );
+}
+
+
 SCH_FIELD* SCH_SYMBOL::AddField( const SCH_FIELD& aField )
 {
     m_fields.push_back( aField );
@@ -1823,7 +1829,7 @@ void SCH_SYMBOL::Show( int nestLevel, std::ostream& os ) const
                                  << '"' << ">\n";
 
     // skip the reference, it's been output already.
-    for( int i = 1; i < GetFieldCount();  ++i )
+    for( int i = 1; i < (int) GetFields().size();  ++i )
     {
         const wxString& value = GetFields()[i].GetText();
 
@@ -2364,15 +2370,15 @@ bool SCH_SYMBOL::operator <( const SCH_ITEM& aItem ) const
 
 bool SCH_SYMBOL::operator==( const SCH_SYMBOL& aSymbol ) const
 {
-    if( GetFieldCount() !=  aSymbol.GetFieldCount() )
-        return false;
-
     std::vector<SCH_FIELD*> fields, otherFields;
 
     GetFields( fields, false );
     aSymbol.GetFields( otherFields, false );
 
-    for( int ii = 0; ii < GetFieldCount(); ii++ )
+    if( fields.size() != otherFields.size() )
+        return false;
+
+    for( int ii = 0; ii < (int) fields.size(); ii++ )
     {
         if( fields[ii]->GetId() == FIELD_T::REFERENCE )
             continue;

eeschema/sch_symbol.h

@@ -570,11 +570,9 @@ public:
                          PROPERTY_BASE* aProperty );
 
     /**
-     * Return the number of fields in this symbol.
+     * Return the next ordinal for a user field for this symbol
      */
-    int GetFieldCount() const { return (int )m_fields.size(); }
-
-    int GetNextFieldId() const { return (int) m_fields.size(); }
+    int GetNextFieldOrdinal() const;
 
     /**
      * Automatically orient all the fields in the symbol.

pcbnew/footprint.h

@@ -696,7 +696,7 @@ public:
     std::deque<PCB_FIELD*>& GetFields() { return m_fields; }
 
     /**
-     * Return the next ID for a field for this footprint
+     * Return the next ordinal for a user field for this footprint
      */
     int GetNextFieldOrdinal() const;
 

pcbnew/pcb_field.cpp

@@ -34,13 +34,11 @@
 PCB_FIELD::PCB_FIELD( FOOTPRINT* aParent, FIELD_T aFieldId, const wxString& aName ) :
         PCB_TEXT( aParent, PCB_FIELD_T ),
         m_id( aFieldId ),
-        m_ordinal( static_cast<int>( aFieldId ) ),
+        m_ordinal( 0 ),
         m_name( aName )
 {
     if( m_id == FIELD_T::USER )
         m_ordinal = aParent->GetNextFieldOrdinal();
-    else
-        m_ordinal = 0;
 }
 
 
@@ -220,10 +218,21 @@ bool PCB_FIELD::operator==( const BOARD_ITEM& aOther ) const
 
 bool PCB_FIELD::operator==( const PCB_FIELD& aOther ) const
 {
-    return m_id == aOther.m_id
-            && m_ordinal == aOther.m_ordinal
-            && m_name == aOther.m_name
-            && EDA_TEXT::operator==( aOther );
+    if( IsMandatory() != aOther.IsMandatory() )
+        return false;
+
+    if( IsMandatory() )
+    {
+        if( m_id != aOther.m_id )
+            return false;
+    }
+    else
+    {
+        if( m_ordinal != aOther.m_ordinal )
+            return false;
+    }
+
+    return m_name == aOther.m_name && EDA_TEXT::operator==( aOther );
 }