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).
Fixes Windows cross compilation for GHC 9.0 and 9.2.
Updates wine to use the version that is included with the chosen Nixpkgs (it used to be pinned to an older version).
Moves the configuration of the GHC source into the GHC derivation. This should make adding Hadrian support easier.
Propagates library dependences (not just pkgconfig ones) on windows so that any DLLs in those libraries can be copied for TH evaluation and to the `/bin` directory of executable components.
Adds gcc and mfcgthreads as library dependencies on Windows so that the DLLs they include will be found.
Use `$pkgsHostTarget` (instead of `ghc-pkg`) to find all the DLLs can copy them to the `/bin` directory of executable components.
Adds support for __int128_t and __uint128_t to language-c to fix aarch64-darwin builds.
Fixed reinstalling packages that come with patched versions in ghcjs.
When downloading a `repository` block we get a number of files (not just the index). For some repositories these files will be necessary for `cabal configure` and the vanilla ones created by haskell.nix will not work. This change keeps these extra files and combines them with the main hackage index using `lndir`, so that changes to the repo will not require a new copy of the hackage index in the store.
This change also introduces `inputMap` that allows flake or niv inputs to be used to pin repository. It also works with `source-repository-package` blocks.
* Improve support for external Hackage repositories
This change builds #535. `repository` blocks in `cabal.project` parsed and `cabal` is used to automatically downloaded them. Then `hackage-to-nix` is used to produce the nix required.
To make it work with restricted eval (on hydra for instance) we need to include a sha256 like this:
```
repository ghcjs-overlay
url: https://input-output-hk.github.io/hackage-overlay-ghcjs
secure: True
root-keys:
key-threshold: 0
--sha256: sha256-EPlLYPmIGtxeahlOspRzwJv+60N5mqrNC2BY4jZKceE=
```
To find the correct `sha256` put in an invalid one and attempt a build.
