boolean_union problem on gmsh 4.9.0+

[quintenstar]

So far working with pygmsh has been great. To being able to create parametric meshes and properly assigning physical labels to all the parts. Definitely would be much harder with pure gmsh.

As part of my mesh creation, I add a bunch of rotated rectangles together. This works perfectly up to gmsh version 4.8-, but fails for gmsh 4.9+ (using the latest pygmsh 7.1.17)

MWE:

import pygmsh
import math

with pygmsh.occ.Geometry() as geom:
   geom.characteristic_length_min = 0.1
   geom.characteristic_length_max = 0.5

   holes = []
   N = 6
   for i in range(N):
       angle = i * 2 * math.pi / N

       hole = geom.add_rectangle((5, 4.5, 0), 4, 1)
       geom.rotate(hole, (5, 5, 0), angle, (0, 0, 1))
       holes.append(hole)

   geom.boolean_union(holes)

   geom.generate_mesh()
   pygmsh.write("test.msh")

Output using gmsh >=4.9.0 :

  Info    : Cannot bind existing OpenCASCADE surface 1 to second tag 2
  Info    : Could not preserve tag of 2D object 2 (->1)
  Info    : Cannot bind existing OpenCASCADE surface 1 to second tag 3
  Info    : Could not preserve tag of 2D object 3 (->1)
  Info    : Cannot bind existing OpenCASCADE surface 1 to second tag 4
  Info    : Could not preserve tag of 2D object 4 (->1)
  Info    : Cannot bind existing OpenCASCADE surface 1 to second tag 5
  Info    : Could not preserve tag of 2D object 5 (->1)
  Info    : Cannot bind existing OpenCASCADE surface 1 to second tag 6
  Info    : Could not preserve tag of 2D object 6 (->1)

Desired output (<=4.8.4) :