Switching between cabal install versions can occur either when developing cabal, or when using nix-shells that bring different versions into scope, among other reasons.

Each time you switch versions, you get Warning: Parsing the index cache failed and it needs to regenerate the index cache.

This can be tedious and time consuming.

I suggest that cabal store its index cache per-cabal-version rather than always in the same spot, thus helping to more frequently avoid this issue.