Bug in Shape.split()

[makerC-LV]

I build an object and split it, and that works. However if I fillet some of the edges before splitting it, there's an error. Here's a minimal example:

import build123d as b3d
from build123d import Align, Axis, Box, Compound, Keep, Location, Plane, Polygon, extrude, faces, fillet, offset, split
from ocp_vscode import show

a = 100
b = 200
c = 50
h = 10
d = 2
o = 25

def example():
    t = Polygon([(0, 0, 0), (a, 0, 0), (a,
                b, 0), (0, c, 0)], align=Align.MIN)
    obj = extrude(t, h)
    top_edges = obj.edges().group_by(Axis.Z)[-1]
    # if the line below is commented out, the example runs, if not, throws error
    # obj = fillet(top_edges, d)

    right = split(obj, bisect_by=Plane.YZ.offset(o), keep=Keep.TOP)
    left = split(obj, bisect_by=Plane.YZ.offset(o), keep=Keep.BOTTOM)
    return [left, right]


show(example())

Observation by Bernhard on Discord:
I think this is a bug in Shape.split: BRepAlgoAPI_Splitter returns a list of one Compound instead of two Solids. If I change

        if keep == Keep.BOTH:
            result = Compound(downcast(splitter.Shape()))
        else:
            parts = list(Compound(downcast(splitter.Shape())))
            tops = []

to

        parts = list(Compound(downcast(splitter.Shape())))
        if len(parts) == 1 and isinstance(parts[0], Compound):
            parts = list(parts[0])

        if keep == Keep.BOTH:
            result = Compound(parts)
        else:
            tops = []

then it works.

[gumyr]

Thanks for pointing this out. The problem with Compounds of Compounds has happened before so I've created an unwrap method for Compounds that remove these redundant layers. With this change the fix looks like:

        result = Compound(downcast(splitter.Shape())).unwrap(fully=False)
        if keep != Keep.BOTH:
            tops = []
            bottoms = []
            for part in result:
                ...

Compounds are full iterables now with a __Len__ method that can help when working with them.