Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/justinwoo/spago2nix

Generate a derivation of (old) Spago dependencies, and use them to install them into the directory structure used by Spago.
https://github.com/justinwoo/spago2nix

nix purescript spago

Last synced: 3 days ago
JSON representation

Generate a derivation of (old) Spago dependencies, and use them to install them into the directory structure used by Spago.

Awesome Lists containing this project

README 

        
# Spago2Nix



![](./logo-256.png)



Generate a derivation of (old) Spago dependencies, and use them to install them into the directory structure used by Spago.



## Warning



This is a project targeting the old versions of Spago and will not be updated to work with the newer versions. This repository remains here for you to read through and fork from, if needed.



## Installation



For now, simply clone this repo and run `npm link`. Requires a Node runtime and nix-prefetch-git.



Remember to set npm prefix to something like `~/.npm`.



## Usage



First, generate the spago-packages.nix:



```bash

$ spago2nix generate

getting packages..

got 65 packages from Spago list-packages.

# ...

wrote spago-packages.nix

```



Then install these, optionally with more jobs provided to Nix:



```bash

$ spago2nix install -j 100

/nix/store/...-install-spago-style

installing dependencies...

# ...

done.

Wrote install script to .spago2nix/install

```



Then build the project:



```bash

$ spago2nix build

/nix/store/...-build-spago-style

building project...

done.

Wrote build script to .spago2nix/build

```



When using in your own Nix derivation, the best practice is calling generated scripts from `spago-packages.nix`:



```nix

{ pkgs, stdenv }:



let

  spagoPkgs = import ./spago-packages.nix { inherit pkgs; };

in

pkgs.stdenv.mkDerivation rec {

  # < ... >

  buildPhase =

  ''

    ${spagoPkgs.installSpagoStyle} # == spago2nix install

    ${spagoPkgs.buildSpagoStyle}   # == spago2nix build

    ${spagoPkgs.buildFromNixStore} # == spago2nix build

  '';

  # < ... >

}

```



## Workflow



The [workflow of `spago2nix`](https://github.com/purescript/spago/issues/547) is:



1. Ensure you have Spago installed, a `packages.dhall` file, and a `spago.dhall`

   file.



2. Run `spago2nix generate` to generate a new `spago-packages.nix` file which

   describes how to build the dependencies.



   You can add `spago2nix` to the `nativeBuildInputs` of a `mkShell` just by

   importing the `spago2nix` repository `default.nix`.



   ```nix

   spago2nix = import (builtins.fetchGit {

     url = "[email protected]:justinwoo/spago2nix.git";

     rev = "...";

   }) { inherit pkgs; };



   pkgs.mkShell {

     nativeBuildInputs = with pkgs; [

       spago2nix

     ];

   ```



   Then you'll be able to run `spago2nix generate` in an impure shell. It will

   call out to the network to look up hashes for the versions of packages

   in your `spago.dhall`.



   The output of `spago2nix generate` will be a `spago-packages.nix` file,

   which contains pure derivations for each package dependency, and which you

   should check into source control.



3. In the Nix expression which describes how to build your project, import

   the generated `spago-packages.nix` file to get the package dependencies.



   ```nix

   spagoPkgs = import ./spago-packages.nix { inherit pkgs; };

   ```



4. When describing the build steps, either use `spago2nix build` or

   `spago build --no-install` or call to the compiler directly

   with `purs compile "src/**/*.purs" ${spagoPackages.compilePaths}`.



   Or do something like this:



   ```nix

   pkgs.stdenv.mkDerivation {

     name = "myderiv";

     buildInputs = [

       spagoPkgs.installSpagoStyle

       spagoPkgs.buildSpagoStyle

       ];

     nativeBuildInputs = with pkgs; [

       easy-ps.purs-0_13_8

       easy-ps.spago

       ];

     src = ./.;

     unpackPhase = ''

       cp $src/spago.dhall .

       cp $src/packages.dhall .

       cp -r $src/src .

       install-spago-style

       '';

     buildPhase = ''

       build-spago-style "./src/**/*.purs"

       '';

     installPhase = ''

       mkdir $out

       mv output $out/

       '';

     }

   ```



This has a key drawback: steps 2 and 3 really ought to be a single step.

Because the `spago.dhall` file doesn't contain any cryptographic verification

of the dependencies, we can't do this as a pure one-step derivation.



## 1-Step Workflow with `flake.nix`



The 1-Step Workflow requires an impure Nix build.



There is a `flake.nix` which provides a package for building a PureScript

project in a Nix derivation. The package is a function

named `spago2nix_nativeBuildInputs` which has a “type signature” like this:



```nix

{

  spago-dhall ? "spago.dhall", # the main spago.dhall file name, i.e. "spago.dhall"

  srcs-dhall # array of .dhall files, i.e. [./spago.dhall ./packages.dhall]

}: []

```



The `spago2nix_nativeBuildInputs` function takes as inputs the PureScript

project’s Spago `.dhall` files, and produces as output an array of

derivations to include in a `nativeBuildInputs`. For a derivation which

has those `nativeBuildInputs`, the PureScript project can be built

in the `buildPhase` by executing `build-spago-style`.



Example:



```nix

stdenv.mkDerivation {

  name = "my-purescript-project";

  nativeBuildInputs = [

    easy-purescript-nix.purs

  ] ++ (

    spago2nix_nativeBuildInputs {

      srcs-dhall = [./spago.dhall ./packages.dhall];

    }

  );

  src = nixpkgs.nix-gitignore.gitignoreSource [ ".git" ] ./.;

  unpackPhase = ''

    cp -r $src/src .

    cp -r $src/test .

    install-spago-style

    '';

  buildPhase = ''

    build-spago-style "./src/**/*.purs" "./test/**/*.purs"

    '';

  installPhase = ''

    mkdir -p $out

    mv output $out/

    '';

}

```



For another example, see [`test-flake/flake.nix`](test-flake/flake.nix)

in this repository which shows how to build the __uint__ package.



The `flake.nix` also has an `app` for running `spago2nix` off of Github,

for example:



```sh

nix run github:justinwoo/spago2nix#spago2nix

```



## Further Reading



Here is a blog post I did about this project: 



## Troubleshooting



#### I get `MissingRevOrRepoResult` on a package with branch name as a version



Nix gives out the specific constant SHA256 hash for broken Git fetches, so the error is thrown.

One of the causes for a broken fetch is wrong checkout revision. Nix supports fetches by commit hash and tags out of the box, but fails at plain branch names.



You can use more verbose reference `refs/heads/branch-name` at `packages.dhall` before generating a `.nix` file.

However, __the branch name usage is discouraged in Spago__ ([refer to Note here](https://github.com/spacchetti/spago#override-a-package-in-the-package-set-with-a-remote-one)), it's better using a particular commit hash.



### I don't know how to compile my project in a derivation



Spago2nix will install and build your project dependencies, but you may still want to use `spago` to bundle your project. You should not use Spago installation or build commands in a derivation. Use Spago's `--no-install` and `--no-build` flags when bundling your project as part of the build phase of a derivation:



```nix

pkgs.stdenv.mkDerivation {

  # < ... >

  buildPhase = ''

    ${spago}/bin/spago bundle-app --no-install --no-build --to $out/index.js

  '';

  # < ... >

};

```



If you attempt to use Spago commands to install or build in your project, you'll see the following error:



```

spago: security: createProcess: runInteractiveProcess: exec: does not exist (No such file or directory)

```