PNS: Improve behavior of dragging vias

- Fall back to walkaround when drag fails
- Properly check collisions with holes

Fixes https://gitlab.com/kicad/code/kicad/-/issues/15117

pcbnew/router/pns_dragger.cpp

@@ -685,6 +685,11 @@ bool DRAGGER::dragShove( const VECTOR2I& aP )
             m_draggedVia = newVia;
 
         m_draggedItems.Clear();
+
+         // If drag didn't work (i.e. dragged onto a collision) try walkaround instead
+        if( !ok )
+            ok = dragViaWalkaround( m_draggedVia, m_lastNode, aP );
+
         break;
     }
     }

pcbnew/router/pns_shove.cpp

@@ -1308,7 +1308,7 @@ SHOVE::SHOVE_STATUS SHOVE::shoveIteration( int aIter )
 
     PNS_DBG( Dbg(), AddItem, &currentLine, RED, currentLine.Width(), wxString::Format( wxT( "current-coll-chk rank %d" ), currentLine.Rank() ) );
 
-    for( ITEM::PnsKind search_order : { ITEM::SOLID_T, ITEM::VIA_T, ITEM::SEGMENT_T } )
+    for( ITEM::PnsKind search_order : { ITEM::HOLE_T, ITEM::SOLID_T, ITEM::VIA_T, ITEM::SEGMENT_T } )
     {
         COLLISION_SEARCH_OPTIONS opts;
         opts.m_kindMask = search_order;
@@ -1343,6 +1343,12 @@ SHOVE::SHOVE_STATUS SHOVE::shoveIteration( int aIter )
 
     ITEM* ni = nearest->m_item;
 
+    UNITS_PROVIDER up( pcbIUScale, EDA_UNITS::MILLIMETRES );
+    PNS_DBG( Dbg(), Message,
+             wxString::Format( wxT( "NI: %s (%s)" ), ni->Format(), ni->Parent()
+                                                ? ni->Parent()->GetItemDescription( &up )
+                                                : "null" ) );
+
     unwindLineStack( ni );
 
     if( !ni->OfKind( ITEM::SOLID_T ) && ni->Rank() >= 0 && ni->Rank() > currentLine.Rank() )
@@ -1793,13 +1799,21 @@ SHOVE::SHOVE_STATUS SHOVE::ShoveDraggingVia( const VIA_HANDLE aOldVia, const VEC
         st = shoveMainLoop();
 
     if( st == SH_OK )
+    {
         runOptimizer( m_currentNode );
 
+        // m_draggedVia will only be updated if pushOrShoveVia makes progress...
+        // this should probably be refactored/cleaned up.
+        PNS::VIA* viaCheck = m_draggedVia ? m_draggedVia : viaToDrag;
+
+        st = m_currentNode->CheckColliding( viaCheck ) ? SH_INCOMPLETE : SH_OK;
+    }
+
     if( st == SH_OK || st == SH_HEAD_MODIFIED )
     {
         wxLogTrace( "PNS","setNewV %p", m_draggedVia );
 
-        if (!m_draggedVia)
+        if( !m_draggedVia )
             m_draggedVia = viaToDrag;
 
         aNewVia = m_draggedVia->MakeHandle();

pcbnew/router/router_tool.cpp

@@ -638,7 +638,9 @@ void ROUTER_TOOL::saveRouterDebugLog()
 
     for( auto item : removed )
     {
-        fprintf(f, "removed %s\n", item->Parent()->m_Uuid.AsString().c_str().AsChar() );
+        fprintf(f, "removed %s\n", item->Parent() ?
+                                   item->Parent()->m_Uuid.AsString().c_str().AsChar() :
+                                   item->Format().c_str() );
     }
 
     for( auto item : added )