Sort PCAD layers

Better fix for 11750.  Instead of figeting with layer values, we sort
our map based on the layer numbers in the PCAD file.  F_Cu is always
layer 1 and B_Cu is always layer 2.

Fixes https://gitlab.com/kicad/code/kicad/issues/11750

pcbnew/plugins/pcad/pcb.cpp

@@ -102,9 +102,6 @@ PCB::PCB( BOARD* aBoard ) :
     m_LayersMap[3].KiCadLayer  = Eco2_User;
     m_LayersMap[6].KiCadLayer  = F_SilkS;
     m_LayersMap[7].KiCadLayer  = B_SilkS;
-
-    m_mappedBottom = false;
-    m_mappedTop = false;
 }
 
 
@@ -459,7 +456,7 @@ int PCB::FindLayer( const wxString& aLayerName ) const
 {
     for( int i = 0; i < (int) m_layersStackup.size(); ++i )
     {
-        if( m_layersStackup[i] == aLayerName )
+        if( m_layersStackup[i].first == aLayerName )
             return i;
     }
 
@@ -495,12 +492,10 @@ void PCB::MapLayer( XNODE* aNode )
     else if( lName == wxT( "TOP" ) )
     {
         KiCadLayer = F_Cu;
-        m_mappedTop = true;
     }
     else if( lName == wxT( "BOTTOM" ) )
     {
         KiCadLayer = B_Cu;
-        m_mappedBottom = true;
     }
     else if( lName == wxT( "BOT MASK" ) )
     {
@@ -529,14 +524,6 @@ void PCB::MapLayer( XNODE* aNode )
         if( layernum == -1 )
             KiCadLayer = Dwgs_User;    // default
         else
-            // Account for ordering (leave room for F.Cu and B.Cu
-            // TODO: Add layer mapping widget
-            if( !m_mappedTop )
-                ++layernum;
-
-            if( m_mappedBottom )
-                --layernum;
-
             KiCadLayer = ToLAYER_ID( layernum );
     }
 
@@ -750,15 +737,20 @@ void PCB::ParseBoard( wxStatusBar* aStatusBar, wxXmlDocument* aXmlDoc,
             {
                 if( FindNode( aNode, wxT( "layerType" ) ) )
                 {
+                    long num = -1;
+
+                    if( FindNode( aNode, wxT( "layerNum" ) ) )
+                        FindNode( aNode, wxT( "layerNum" ) )->GetNodeContent().ToLong( &num );
+
                     layerType = FindNode( aNode, wxT( "layerType" ) )->GetNodeContent().Trim(
                             false );
 
-                    if( layerType.IsSameAs( wxT( "Signal" ), false )
-                            || layerType.IsSameAs( wxT( "Plane" ), false ) )
+                    if( num > 0 && ( layerType.IsSameAs( wxT( "Signal" ), false )
+                            || layerType.IsSameAs( wxT( "Plane" ), false ) ) )
                     {
                         aNode->GetAttribute( wxT( "Name" ), &layerName );
                         layerName = layerName.MakeUpper();
-                        m_layersStackup.emplace_back( layerName );
+                        m_layersStackup.emplace_back( layerName, num );
 
                         if( m_layersStackup.size() > 32 )
                             THROW_IO_ERROR( _( "KiCad only supports 32 signal layers." ) );
@@ -768,6 +760,16 @@ void PCB::ParseBoard( wxStatusBar* aStatusBar, wxXmlDocument* aXmlDoc,
 
             aNode = aNode->GetNext();
         }
+
+        // Ensure that the layers are properly mapped to their order with the bottom
+        // copper (layer 2 in PCAD) at the end
+        std::sort( m_layersStackup.begin(), m_layersStackup.end(),
+        [&]( const std::pair<wxString, long>& a, const std::pair<wxString, long>& b ) {
+            long lhs = a.second == 2 ? std::numeric_limits<long>::max() : a.second;
+            long rhs = b.second == 2 ? std::numeric_limits<long>::max() : b.second;
+
+            return lhs < rhs;
+        } );
     }
 
     // Layers mapping

pcbnew/plugins/pcad/pcb.h

@@ -83,9 +83,7 @@ private:
     double GetDistance( const wxRealPoint* aPoint1, const wxRealPoint* aPoint2 ) const;
     void GetBoardOutline( wxXmlDocument* aXmlDoc, const wxString& aActualConversion );
 
-    std::vector<wxString>   m_layersStackup;
-    bool                    m_mappedTop;
-    bool                    m_mappedBottom;
+    std::vector<std::pair<wxString, long>>   m_layersStackup;
 };
 
 } // namespace PCAD2KICAD