mesh boolean node breaks material assignments. #93272

System Information
Operating system: Windows-10-10.0.19042-SP0 64 Bits
Graphics card: NVIDIA GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 472.12

Blender Version
Broken: version: 3.1.0 Alpha, branch: master, commit date: 2021-11-11 18:53, hash: 0533f2851e
Worked: (newest version of Blender that worked as expected)

Open below file. Left cube has no manually added shaders in the properties panel, middle cube does. The first 2 cubes are incorrect, the third cube is what should have happened.

boolean breaks material assignments.blend

Error 1:

left cube's cutter object materials are not transferred to the resulting object.

Error 2:
Middle cube is assigned material 'c' (blue) to face 3 rather than the specified material 'b' (green), and the rest of the cut out is given material 'b' (green) even though material 'a' was specified for the rest of the small cutter cube.

Added subscriber: @3di

#94261 was marked as duplicate of this issue

Added subscribers: @JacquesLucke, @howardt

@howardt @JacquesLucke asked me to create this new job. Just letting you know as he added you in the old one which is now closed. 👍

Added subscriber: @lichtwerk

Changed status from 'Needs Triage' to: 'Confirmed'

reg. Error 1: since Set Material is only setting material_index, I was under the impression the materials need to be assigned to the object already, no?
Not quite sure why this works (without the boolean) to begin with tbh.
https://docs.blender.org/manual/en/dev/modeling/geometry_nodes/material/set_material.html

reg. Error 2: yep, would also think it is a bug. I can only assume this has to do with the fact that this happens in the "branch" of the tree where only the Mesh Primitive Cube is handled (and the "original" Group Input geometry is not in that branch)... Then, the material index seems to "off by one" (to high) Surprisingly, using the Set Material Index node instead works better here:
boolean breaks material assignments set_material_index instead of set_material.blend

Might be related:

#93319
#93177#1255723

@JacquesLucke: this is not expected behavior, right?

Any idea of when this might get looked at? Not rushing anyone, just need to organise around it if it's going to be ages.

Added subscriber: @ChrisGauthier

This issue was referenced by f80e4f0046

This issue was referenced by 1a6d0ec71c

Changed status from 'Confirmed' to: 'Resolved'

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mesh boolean node breaks material assignments. #93272