Special-case clearances of NPTH pads with no copper on layer.

These should get the hole clearance, not the copper clearance.

Fixes https://gitlab.com/kicad/code/kicad/issues/4017

pcbnew/class_pad.cpp

@@ -641,6 +641,35 @@ int D_PAD::GetLocalClearance( wxString* aSource ) const
 }
 
 
+int D_PAD::GetClearance( PCB_LAYER_ID aLayer, BOARD_ITEM* aItem, wxString* aSource ) const
+{
+    DRC_CONSTRAINT constraint;
+
+    if( GetBoard() && GetBoard()->GetDesignSettings().m_DRCEngine )
+    {
+        BOARD_DESIGN_SETTINGS& bds = GetBoard()->GetDesignSettings();
+        DRC_CONSTRAINT_TYPE_T  constraintType = DRC_CONSTRAINT_TYPE_CLEARANCE;
+
+        // A PTH pad has a plated cylinder around the hole so copper clearances apply
+        // whether or not there's a flashed pad.  Not true for NPTHs.
+        if( GetAttribute() == PAD_ATTRIB_NPTH && !FlashLayer( aLayer ) )
+            constraintType = DRC_CONSTRAINT_TYPE_HOLE_CLEARANCE;
+
+        constraint = bds.m_DRCEngine->EvalRulesForItems( constraintType, this, aItem, aLayer );
+    }
+
+    if( constraint.Value().HasMin() )
+    {
+        if( aSource )
+            *aSource = constraint.GetName();
+
+        return constraint.Value().Min();
+    }
+
+    return 0;
+}
+
+
 // Mask margins handling:
 
 int D_PAD::GetSolderMaskMargin() const

pcbnew/class_pad.h

@@ -366,6 +366,20 @@ public:
     double GetLocalSolderPasteMarginRatio() const { return m_localSolderPasteMarginRatio; }
     void SetLocalSolderPasteMarginRatio( double aRatio ) { m_localSolderPasteMarginRatio = aRatio; }
 
+    /**
+     * Function GetClearance
+     * returns the clearance in internal units.  If \a aItem is not NULL then the
+     * returned clearance is the greater of this object's NETCLASS clearance and
+     * aItem's NETCLASS clearance.  If \a aItem is NULL, then this objects clearance
+     * is returned.
+     * @param aLayer the layer in question
+     * @param aItem is an optional BOARD_ITEM
+     * @param aSource [out] optionally reports the source as a user-readable string
+     * @return int - the clearance in internal units.
+     */
+    int GetClearance( PCB_LAYER_ID aLayer, BOARD_ITEM* aItem = nullptr,
+                      wxString* aSource = nullptr ) const override;
+
     /**
      * Function TransformShapeWithClearanceToPolygon
      * Convert the pad shape to a closed polygon. Circles and arcs are approximated by segments.