Fix handling of circles on outline layer

gerbonara/graphic_primitives.py

@@ -212,6 +212,10 @@ class Arc(GraphicPrimitive):
     #: Line width of this arc.
     width : float
 
+    @property
+    def is_circle(self):
+        return math.isclose(self.x1, self.x2) and math.isclose(self.y1, self.y2)
+
     def flip(self):
         return replace(self, x1=self.x2, y1=self.y2, x2=self.x1, y2=self.y1,
             cx=(self.x1 + self.cx) - self.x2, cy=(self.y1 + self.cy) - self.y2, clockwise=not self.clockwise)

gerbonara/layers.py

@@ -1140,6 +1140,12 @@ class LayerStack:
 
         joins = {}
         for cur in lines:
+            # Special case: An arc may describe a complete circle, in which case we have to return it as-is since it
+            # is the only primitive that can join itself.
+            if isinstance(cur, gp.Arc) and cur.is_circle:
+                yield [cur]
+                continue
+
             for (i, x, y) in [(0, cur.x1, cur.y1), (1, cur.x2, cur.y2)]:
                 x_left  = bisect.bisect_left (by_x, x, key=lambda elem: elem[0] + tol)
                 x_right = bisect.bisect_right(by_x, x, key=lambda elem: elem[0] - tol)