internal error: evacuate: strange closure type

Summary

I get a "internal error: evacuate: strange closure type" error during execution. The error message indicates it's a GHC bug.

Steps to reproduce

$ git clone -b ghc_bug/strange-closure https://github.com/pchiusano/unison.git
$ cd unison
$ stack build
$ stack exec unison -- -codebase ghcbug

The build finishes fine and it bombs right away during execution with:

unison: internal error: evacuate: strange closure type 2138194
    (GHC version 8.10.4 for x86_64_apple_darwin)
    Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug
[1]    24284 abort      stack exec unison -- -codebase ghcbug

The number 2138194 is different each time and seems random, though I've seen 0 pretty regularly.

Expected behavior

Not crash. :)

Environment

• GHC version used: 8.10.4

Optional:

• Operating System: MacOS 11.2.3
• System Architecture: x86_64 apple darwin