Documentation: v1 to v2 migration guide.

[phadej]

cabal-install-3.0 changelog / release notes should point out to that part of documentation as the first things.

There will be a lot of confusion when 3.0 is released, and there are no migration guide explaining how v2-build or v2-install are different from v1-build or v1-install. The QuickStart section is not the right one, as it doesn't explain the differences.

[23Skidoo]

BTW, I've started writing a 3.0 migration guide for custom Setup authors: https://github.com/haskell/cabal/wiki/3.0-migration-guide. Help appreciated...

[okeuday]

Please describe in the migration guide what to do with the v2 (Nix-style local builds) commands to get the same sandbox functionality that was present with the v1 sandbox command.

[phadej]

There are no sandboxes in v2 workflows. They are unneeded.

[23Skidoo]

Right, but the migration guide should explain why.

[GeorgeCo]

I think it is important to get this into 3.2 and if possible something on ghc-pkg, if only a reference to the ghc issue: #6342