GHC bug! Heap Overflow error during Cabal Install - Panic! (the 'impossible' happened)

using: cabal install --ghc-options="+RTS -M2G" -j1 --force-reinstalls Agda Trying to install Agda 2.6.1.2 for about the fifth time.

The following was returned:

. . . [297 of 369] Compiling Agda. Typechecking.Rules.LHS.Unify ( src/full/Agda/TypeChecker: panic! (the 'impossible' happened) (GHC version 8.8.4 for x86_64-unknown-linux): heap overflow

Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug

cabal: Failed to build Agda-2.6.1.2

(Am using Ubuntu 20.04.01 LTS, I was trying to control the heap overflow problem with -M2G as I only have 4GB memory - I'm quite happy to leave it running for a few hours, but it should still work eventually!!)

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