PNS: Fix yet more arc edge cases

Fixes https://gitlab.com/kicad/code/kicad/-/issues/8150

libs/kimath/src/geometry/shape_line_chain.cpp

@@ -318,21 +318,26 @@ void SHAPE_LINE_CHAIN::Replace( int aStartIndex, int aEndIndex, const SHAPE_LINE
 
     if( startShape >= 0 )
     {
-        wxASSERT( newLine.m_points.front() == m_points[aStartIndex] &&
+        wxASSERT( !newLine.PointCount() ||
-                  aStartIndex < m_points.size() - 1 );
+                  ( newLine.m_points.front() == m_points[aStartIndex] &&
+                  aStartIndex < m_points.size() - 1 ) );
         aStartIndex++;
         newLine.Remove( 0 );
     }
 
     if( endShape >= 0 )
     {
-        wxASSERT( newLine.m_points.back() == m_points[aEndIndex] && aEndIndex > 0 );
+        wxASSERT( !newLine.PointCount() ||
+                  ( newLine.m_points.back() == m_points[aEndIndex] && aEndIndex > 0 ) );
         aEndIndex--;
         newLine.Remove( -1 );
     }
 
     Remove( aStartIndex, aEndIndex );
 
+    if( !aLine.PointCount() )
+        return;
+
     // The total new arcs index is added to the new arc indices
     size_t               prev_arc_count = m_arcs.size();
     std::vector<ssize_t> new_shapes     = newLine.m_shapes;

pcbnew/router/pns_line.cpp

@@ -574,6 +574,10 @@ void LINE::dragCorner45( const VECTOR2I& aP, int aIndex )
         path = dragCornerInternal( m_line, snapped );
     else
     {
+        // Are we next to an arc? Insert a new point so we slice correctly
+        if( m_line.CShapes()[aIndex + 1] >= 0 )
+            m_line.Insert( aIndex + 1, m_line.CPoint( aIndex + 1 ) );
+
         // fixme: awkward behaviour for "outwards" drags
         path = dragCornerInternal( m_line.Slice( 0, aIndex ), snapped );
         SHAPE_LINE_CHAIN path_rev =
@@ -594,7 +598,7 @@ void LINE::dragCornerFree( const VECTOR2I& aP, int aIndex )
     {
         if( aIndex > 0 && shapes[aIndex - 1] == -1 )
             m_line.Insert( aIndex, m_line.GetPoint( aIndex ) );
-        else if( aIndex < shapes.size() - 1 && shapes[aIndex + 1] == -1 )
+        else if( aIndex < shapes.size() - 1 && shapes[aIndex + 1] != shapes[aIndex] )
         {
             aIndex++;
             m_line.Insert( aIndex, m_line.GetPoint( aIndex ) );
@@ -730,9 +734,16 @@ void LINE::dragSegment45( const VECTOR2I& aP, int aIndex )
 
     target = snapToNeighbourSegments( path, aP, aIndex );
 
-    if( index == 0 )
+    const std::vector<ssize_t>& shapes = path.CShapes();
+
+    // We require a valid s_prev and s_next.  If we are at the start or end of the line, we insert
+    // a new point at the start or end so there is a zero-length segment for prev or next (we will
+    // resize it as part of the drag operation).  If we are next to an arc, we do this also, as we
+    // cannot drag away one of the arc's points.
+
+    if( index == 0 || shapes[index] >= 0 )
     {
-        path.Insert( 0, path.CPoint( 0 ) );
+        path.Insert( index > 0 ? index + 1 : 0, path.CPoint( index ) );
         index++;
     }
 
@@ -740,6 +751,10 @@ void LINE::dragSegment45( const VECTOR2I& aP, int aIndex )
     {
         path.Insert( path.PointCount() - 1, path.CPoint( -1 ) );
     }
+    else if( shapes[index + 1] >= 0 )
+    {
+        path.Insert( index + 1, path.CPoint( index + 1 ) );
+    }
 
     SEG          dragged = path.CSegment( index );
     DIRECTION_45 drag_dir( dragged );
@@ -756,12 +771,20 @@ void LINE::dragSegment45( const VECTOR2I& aP, int aIndex )
         path.Insert( index, path.CPoint( index ) );
         index++;
     }
+    else if( dir_prev == DIRECTION_45::UNDEFINED )
+    {
+        dir_prev = drag_dir.Left();
+    }
 
     if( dir_next == drag_dir )
     {
         dir_next = dir_next.Right();
         path.Insert( index + 1, path.CPoint( index + 1 ) );
     }
+    else if( dir_next == DIRECTION_45::UNDEFINED )
+    {
+        dir_next = drag_dir.Right();
+    }
 
     s_prev = path.CSegment( index - 1 );
     s_next = path.CSegment( index + 1 );