mirror of
https://github.com/simplex-chat/haskell.nix.git
synced 2026-06-03 09:17:32 +00:00
Asad Saeeduddin
3250b6cc7b
It seems [Hercules CI](https://hercules-ci.com/github/input-output-hk/haskell.nix) is having some problems, which means build outputs might not be available via the Cachix substituter.
128 lines
4.4 KiB
Markdown
128 lines
4.4 KiB
Markdown
# Getting started
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`haskell.nix` can automatically translate your
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[Cabal](https://cabal.readthedocs.io/en/latest/cabal-project.html)
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or [Stack](https://docs.haskellstack.org/en/stable/README/#quick-start-guide)
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project and its dependencies into Nix code.
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Assuming you have [Nix](https://nixos.org/download.html) installed, you can
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start setting up your project.
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## Setting up the Cachix binary cache
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You can **avoid compiling GHC and nix-tools** by configuring
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[Cachix](https://cachix.org) so you can benefit from the binary cache built by
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CI:
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```bash
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$ nix-env -iA cachix -f https://cachix.org/api/v1/install
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installing 'cachix-0.3.8'
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building '/nix/store/bh176xhpk4wrjm56iahm86wf85jaz23v-user-environment.drv'...
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created 42 symlinks in user environment
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$ cachix use iohk
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Configured https://iohk.cachix.org binary cache in ~/.config/nix/nix.conf
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```
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Note: `haskell.nix` currently uses multiple CI providers to build derivations and store outputs. To improve your chances of getting a cache hit, you might want to add the following additional substituter to `~/.config/nix/nix.conf`:
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```
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trusted-public-keys = [...] hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= [...]
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substituters = [...] https://hydra.iohk.io [...]
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```
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## Scaffolding
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The following work with `stack.yaml` and `cabal.project` based
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projects.
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Add `default.nix`:
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```nix
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{ # Fetch the latest haskell.nix and import its default.nix
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haskellNix ? import (builtins.fetchTarball "https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz") {}
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# haskell.nix provides access to the nixpkgs pins which are used by our CI,
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# hence you will be more likely to get cache hits when using these.
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# But you can also just use your own, e.g. '<nixpkgs>'.
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, nixpkgsSrc ? haskellNix.sources.nixpkgs-2003
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# haskell.nix provides some arguments to be passed to nixpkgs, including some
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# patches and also the haskell.nix functionality itself as an overlay.
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, nixpkgsArgs ? haskellNix.nixpkgsArgs
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# import nixpkgs with overlays
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, pkgs ? import nixpkgsSrc nixpkgsArgs
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}: pkgs.haskell-nix.project {
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# 'cleanGit' cleans a source directory based on the files known by git
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src = pkgs.haskell-nix.haskellLib.cleanGit {
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name = "haskell-nix-project";
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src = ./.;
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};
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# For `cabal.project` based projects specify the GHC version to use.
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compiler-nix-name = "ghc884"; # Not used for `stack.yaml` based projects.
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}
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```
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!!! note "git dependencies"
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If you have git dependencies in your project, you'll need
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to [calculate sha256 hashes for them](./source-repository-hashes.md).
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### Working with a project
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Top-level attributes are Haskell packages (incl. dependencies) part of your project.
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To build the library component of a package in the project run:
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```shell
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nix-build -A your-package-name.components.library
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```
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There are also other components such as `exes`, `tests`, `benchmarks` and `all`.
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To build an executable:
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```shell
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nix-build -A your-package-name.components.exes.your-exe-name
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```
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To open a shell for use with `cabal` run:
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```shell
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nix-shell -A shellFor
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cabal new-repl your-package-name:library:your-package-name
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cabal new-build your-package-name
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```
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To open a shell for use with `stack` see [the following issue](https://github.com/input-output-hk/haskell.nix/issues/689#issuecomment-643832619).
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### Pinning the [haskell.nix][] version
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For simplicity's sake we will use `fetchTarball` for the examples in
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this documentation. This will always get the latest version, and is
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similar to an auto-updating Nix channel.
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However, in your own project, you may wish to pin [haskell.nix][] (as
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you would pin Nixpkgs). This will make your builds reproducible, more
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predictable, and faster (because the fixed version is cached).
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Straightforward way of doing this is to change the branch name to a revision.
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```nix
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{ # Fetch a specific haskell.nix and import its default.nix
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haskellNix ? import (builtins.fetchTarball "https://github.com/input-output-hk/haskell.nix/archive/f1a94a4c82a2ab999a67c3b84269da78d89f0075.tar.gz") {}
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...
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```
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There are other possible schemes for pinning. See
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[Bumping Hackage and Stackage snapshots](./hackage-stackage.md) and
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[Nix tutorial on reproducibility using pinning](https://nix.dev/tutorials/towards-reproducibility-pinning-nixpkgs.html).
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## Going forward
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Read through [project](../reference/library.md#project) function reference to see how the API works.
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There are a number of things to explore further in the tutorials section.
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[haskell.nix]: https://github.com/input-output-hk/haskell.nix
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