Revise restriction on No Copper setting

This allows the user to specify a NPTH with "No Copper", allowing a pad
to retain the mask layer without a copper landing.

Fixes https://gitlab.com/kicad/code/kicad/issues/3407

Fixes https://gitlab.com/kicad/code/kicad/issues/5237

pcbnew/dialogs/dialog_pad_properties.cpp

@@ -1197,18 +1197,11 @@ bool DIALOG_PAD_PROPERTIES::padValuesOK()
 
     if( !padlayers_mask[F_Cu] && !padlayers_mask[B_Cu] )
     {
-        if( m_dummyPad->GetDrillSize().x || m_dummyPad->GetDrillSize().y )
+        if( ( m_dummyPad->GetDrillSize().x || m_dummyPad->GetDrillSize().y )
+                && m_dummyPad->GetAttribute() != PAD_ATTRIB_HOLE_NOT_PLATED )
         {
             // Note: he message is shown in an HTML window
-            msg = _( "Error: the pad is not on a copper layer and has a hole" );
-
-            if( m_dummyPad->GetAttribute() == PAD_ATTRIB_HOLE_NOT_PLATED )
-            {
-                msg += wxT( "<br><br><i>" );
-                msg += _( "For NPTH pad, set pad size value to pad drill value,"
-                          " if you do not want this pad plotted in gerber files" );
-            }
-
+            msg = _( "Error: plated through holes must have a copper pad on at least one layer" );
             error_msgs.Add( msg );
         }
     }

pcbnew/router/pns_kicad_iface.cpp

@@ -581,8 +581,9 @@ std::unique_ptr<PNS::SOLID> PNS_KICAD_IFACE_BASE::syncPad( D_PAD* aPad )
 {
     LAYER_RANGE layers( 0, MAX_CU_LAYERS - 1 );
 
-    // ignore non-copper pads
-    if( ( aPad->GetLayerSet() & LSET::AllCuMask()).none() )
+    // ignore non-copper pads except for those with holes
+    if( ( aPad->GetLayerSet() & LSET::AllCuMask()).none() &&
+            aPad->GetAttribute() != PAD_ATTRIB_HOLE_NOT_PLATED )
         return NULL;
 
     switch( aPad->GetAttribute() )
@@ -590,9 +591,9 @@ std::unique_ptr<PNS::SOLID> PNS_KICAD_IFACE_BASE::syncPad( D_PAD* aPad )
     case PAD_ATTRIB_STANDARD:
         break;
 
-    case PAD_ATTRIB_SMD:
     case PAD_ATTRIB_HOLE_NOT_PLATED:
     case PAD_ATTRIB_CONN:
+    case PAD_ATTRIB_SMD:
         {
             LSET lmsk = aPad->GetLayerSet();
             bool is_copper = false;
@@ -610,7 +611,8 @@ std::unique_ptr<PNS::SOLID> PNS_KICAD_IFACE_BASE::syncPad( D_PAD* aPad )
                 }
             }
 
-            if( !is_copper )
+            /// Keep the NPTH pads because we will use the drill as alternate shape
+            if( !is_copper && aPad->GetAttribute() != PAD_ATTRIB_HOLE_NOT_PLATED )
                 return NULL;
         }
         break;