* 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.
There are now 4 project modules used to check the arguments passed to the various project functions:
* `project-common.nix` - Arguments used by all the project functions
* `stack-project.nix` - Used by the `stackProject` and `stackProject'` functions
* `cabal-project.nix` - Used by the `cabalProject` and `cabalProject'` functions
* `project.nix` - Just the `projectFileName` argument that is used by `project` and `project'` functions to determine whether to call `stackProject` or `cabalProject` function.
This also includes the `rawProject.args` that was mistakenly left out of #1141 causing #1142 and improvements for the docs for the use of the `shell` argument in `flake.nix` files.
The default shell `devShell` works by adding a default `shell` to all projects. You can pass the shell arguments to the project function using the new `shell` argument:
```
let myProject = haskell-nix.project {
src = ./.;
shell.tools = { cabal = {}; };
shell.crossPlatforms = p: [ p.cross ];
};
```
This will include js-unknown-ghcjs-cabal in the `devShell`.
To add cross compiled outputs to the flake pass `crossPlatforms` to the `flake` function.
```
myProject.flake { crossPlatforms = p: [ p.cross ]; }
```
To cross compile a component include the platforms `config` string to the output name like this
```
nix build .#js-unknown-ghcjs:pkg-name:lib:pkg-name
```
* Use nix module system to check project arguments
This change uses the nix module system for the arguments to:
* `cabalProject'`
* `cabalProject`
* `stackProject'`
* `stackProject`
This will:
* Give an error when the name or type of an argument is incorrect
(currently misnamed args are quietly ignored).
* Fixes a problem with `projectCross` not having a way to pass different args to `cabalProject`
for different platforms. We can now use:
`({pkgs, ...}: { cabalProjectLocal = if pkgs.stdenv.hostPlatform.isX then ... })`
Hamish Mackenzie
Hamish Mackenzie