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https://github.com/noteed/multiple-ghc-versions
Learning to use multiple GHC versions with a Nix-based Haskell project.
https://github.com/noteed/multiple-ghc-versions
Last synced: about 2 months ago
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Learning to use multiple GHC versions with a Nix-based Haskell project.
- Host: GitHub
- URL: https://github.com/noteed/multiple-ghc-versions
- Owner: noteed
- Created: 2024-03-08T17:02:22.000Z (10 months ago)
- Default Branch: main
- Last Pushed: 2024-03-08T20:19:29.000Z (10 months ago)
- Last Synced: 2024-03-09T18:38:33.060Z (10 months ago)
- Language: Nix
- Size: 15.6 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Experimenting with multiple GHC versions under Nix
Note: having a look at the Git history from this repository may help.
# Trying horizon-haskell.
I want to try to use horizon-haskell to provide different GHC versions and
related packages. It is using flakes, but it is possible to use
`builtins.getFlake` in a project that doens't have a `flake.nix` file.
I have a working use case in Ream.
In this directory, I experiment with two dummy Haskell projects, A and B, with
B depending on A. The way I setup my Haskell projects is derived from how it
was done in Curiosity. It is done in a `nix/` directory providing
`contents.nix`, `overlay.nix`, and `overlays.nix`. The second depends on the
first, and the third depends on the second. Finally, `default.nix` import a
`nixpkgs` using the third as an overlay.
When creating a project that depends on another one (e.g. Curiosity depends on
Commence), the `overlays.nix` from the dependencies are explicitely imported in
a single list in `overlays.nix`.
I think that in the case of horizon-haskell, I should expose the overriding
function (usually called `overrides` in `contents.nix` (instead of in
`overlay.nix`), so that I can use that instead of `overlays.nix`.
To check that this works as intended, I create two projects in this directory,
A and B, using the existing approach, then I'll modify them as described above.
So it works. With the previous overlay approach, all the dependencies overlays
are listed in `overlays.nix`. For horizon-platform, all the overriding
functions are listed in `overlay.nix` instead.
# Multiple GHC versions
Independently from horizon-haskell, this shows how to build project A and B
with a different GHC version than the default one (the default is ghc928):
```
$ cd a # or b
$ nix-build -A binaries --no-out-link --argstr compiler ghc942
$ nix-build -A binaries --no-out-link --argstr compiler ghc962
```
Building with ghc962 doesn't work. (I think template-haskell 2.20 is selected,
but language-haskell-extract need `<2.16`.)
Note: with this change (the `compiler` argument), in `overlay.nix`, we no
longer define `haskellPackages` in term of `haskellPackages`, but in term of
`haskell.packages."${compiler}"`, and we have to pass all the "overrides",
instead of being able to build on top of `old.overrides` with only our current
`contents.overrides`.
# Multiple Nixpkgs versions
Similarly to having multiple GHC versions, it might be useful to be able to
build a package against multiple Nixpkgs versions.
To do that, we introduce a `pkgssrc` argument to the `default.nix` file, that
must be provided by `sources.json`. Such an alternative Nixpkgs can be added
for instance with:
```
$ niv add NixOS/nixpkgs -n nixos-23.10 -b nixos-23.11
```
Given multiple Nixpkgs in `sources.json`, we can select the one we want with:
```
$ nix-build -A binaries --no-out-link --argstr pkgssrc nixos-23.11
```
# Combinations
The different versions of both GHC and Nixpkgs can be combined. To list and
build easily those combinations, a `release.nix` file is provided.
# Resources
This repository uses Nix and Haskell without flakes, and has multiple GHC
versions: https://github.com/awakesecurity/proto3-suite.
I've seen repository that don't use Nix use this kind of things:
https://github.com/haskell-actions/. Servant is one example.
# TODO
I'm wondering how, if necessary, I should work on
https://github.com/jhickner/smtp-mail or https://github.com/tibbe/template.
They were repositories that are not present in horizon-platform.