This adds a way to specify the `evalSystem` or `evalPackages` explicitly when calling the `project` functions.
Currently if we want to make a `flake` that supports multiple systems we have few options:
* Require builders for all the supported systems (even just for `nix flake show`).
* Pass `--impure` so that haskell.nix can see `builtins.currentSystem` to set up `pkgs.evalPackages` to use that. Unfortunately this prevents nix from caching some of the work it does and often results in it recalculating for each supported system when it would otherwise be cached and take no time at all.
* Add an overlay to replace `evalPackages`. This works, but it is not straight forward.
* Materialize the nix files for the project.
This change allows `evalSystem = "x86_64-linux";` to be passed telling `haskell.nix` to run `cabal` and `nix-tools` on that system. The user will have to have a builder for that system, but does not need to have builders for the others (unless building outputs for them).
* Include `tests` in path for cross compiled tests
* Add ghc-boot-packages-nix to haskellNixRoots
* Fix naming warnings in tests sources
* Uses a single cleanGit call for all the tests
* Add memoize code for ghc-boot and ghc-extra pkgs
* Memoize ghc-boot and ghc-extra pkgs nix
* Fix release.nix being more strict than ci.nix by updating filterAttrsOnlyRecursive in ci-lib.nix
* Nicer errors when materialized path does not exist
* Updated materialization docs
* Add internalHackageIndexState to set the index-state used within haskell.nix
If the .nix files listed in the cache are full paths pointing at the
store we get errors like this in restricted eval mode:
error: access to path '/nix/store/...-cabal-simple.nix' is forbidden
in restricted mode
Hamish Mackenzie
Shea Levy
Hamish Mackenzie