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).
Generalized version of the `cabalProject` and `stackProject`
functions.
Automatically selects the correct project type based on the
`projectFileName` argument if provided or what files exist in
the `src` directory if no `projectFileName` was specified.
If it cannot be determined which it should use the following
error message is given:
```
error: haskell-nix.project : both `stack.yaml` and `cabal.project` files exist set `projectFileName = "stack.yaml;"` or `projectFileName = "cabal.project";`
```
* 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
