5. Nix-style Local Builds

Nix-style local builds are a new build system implementation inspired by Nix. The Nix-style local build system is commonly called “new-build” for short after the cabal new-* family of commands that control it. However those names are only temporary until Nix-style local builds becomes the default.

Nix-style local builds combine the best of non-sandboxed and sandboxed Cabal:

  1. Like sandboxed Cabal today, we build sets of independent local packages deterministically and independent of any global state. new-build will never tell you that it can’t build your package because it would result in a “dangerous reinstall.” Given a particular state of the Hackage index, your build is completely reproducible. For example, you no longer need to compile packages with profiling ahead of time; just request profiling and new-build will rebuild all its dependencies with profiling automatically.
  2. Like non-sandboxed Cabal today, builds of external packages are cached in ~/.cabal/store, so that a package can be built once, and then reused anywhere else it is also used. No need to continually rebuild dependencies whenever you make a new sandbox: dependencies which can be shared, are shared.

Nix-style local builds were first released as beta in cabal-install 1.24. They currently work with all versions of GHC supported by that release: GHC 7.0 and later.

Some features described in this manual are not implemented. If you need them, please give us a shout and we’ll prioritize accordingly.