Fp editor: avoid having nil uuids when editing old footprints.

In Fpeditor, nil uuid has a special meaning and cannot be used as uuid in fp items.
Fixes #8914
https://gitlab.com/kicad/code/kicad/issues/8914

pcbnew/footprint.cpp

@@ -221,6 +221,44 @@ FOOTPRINT::~FOOTPRINT()
 }
 
 
+bool FOOTPRINT::FixUuids()
+{
+    // replace null UUIDs if any by a valid uuid
+    std::vector< BOARD_ITEM* > item_list;
+
+    item_list.push_back( m_reference );
+    item_list.push_back( m_value );
+
+    for( PAD* pad : m_pads )
+        item_list.push_back( pad );
+
+    for( BOARD_ITEM* gr_item : m_drawings )
+        item_list.push_back( gr_item );
+
+    // Note: one cannot fix null UUIDs inside the group, but it should not happen
+    // because null uuids can be found in old footprints, therefore without group
+    for( PCB_GROUP* group : m_fp_groups )
+        item_list.push_back( group );
+
+    // Probably notneeded, because old fp do not have zones. But just in case.
+    for( FP_ZONE* zone : m_fp_zones )
+        item_list.push_back( zone );
+
+    bool changed = false;
+
+    for( BOARD_ITEM* item : item_list )
+    {
+        if( item->m_Uuid == niluuid )
+        {
+            const_cast<KIID&>( item->m_Uuid ) = KIID();
+            changed = true;
+        }
+    }
+
+    return changed;
+}
+
+
 FOOTPRINT& FOOTPRINT::operator=( FOOTPRINT&& aOther )
 {
     BOARD_ITEM::operator=( aOther );

pcbnew/footprint.h

@@ -134,6 +134,15 @@ public:
      */
     void ClearAllNets();
 
+    /**
+     * Old footprints do not alway have a valid UUID (some can be set to null uuid)
+     * However null UUIDs, having a special meaning in editor, create issues when
+     * editing a footprint
+     * So all null uuids a re replaced by a valid uuid
+     * @return true if at least one uuid is changed, false if no change
+     */
+    bool FixUuids();
+
     /**
      * Return the bounding box containing pads when the footprint is on the front side,
      * orientation 0, position 0,0.

pcbnew/footprint_edit_frame.cpp

@@ -461,6 +461,9 @@ void FOOTPRINT_EDIT_FRAME::AddFootprintToBoard( FOOTPRINT* aFootprint )
     m_footprintNameWhenLoaded = aFootprint->GetFPID().GetLibItemName();
 
     PCB_BASE_EDIT_FRAME::AddFootprintToBoard( aFootprint );
+    // Ensure item UUIDs are valide
+    // ("old" footprints can have null uuids that create issues in fp editor)
+    aFootprint->FixUuids();
 
     if( IsCurrentFPFromBoard() )
     {

pcbnew/footprint_libraries_utils.cpp

@@ -1,7 +1,7 @@
 /*
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
- * Copyright (C) 1992-2019 KiCad Developers, see AUTHORS.txt for contributors.
+ * Copyright (C) 1992-2021 KiCad Developers, see AUTHORS.txt for contributors.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License