如何利用Stackage的cabal.config配置Nix风格Cabal项目？

Great question! Let's break this down into two clear parts—using a Stackage cabal.config with cabal new-configure, and alternative approaches for Nix-style Cabal projects that leverage Stackage snapshot versions.

This is straightforward and ensures your project uses the exact package versions validated in a Stackage snapshot:

1. First, download the cabal.config file for your target Stackage snapshot (either an LTS release or Nightly build). You can find this file linked directly on the snapshot's main page.
2. Place the file in your project's root directory, or note its full file path if you keep it elsewhere.
3. Run the configure command, pointing to the config file if it's not in your project root:

   cabal new-configure --config-file=/path/to/your/cabal.config
   

   If you placed cabal.config directly in your project root, you can skip the flag—Cabal will automatically detect and use it when you run:

   cabal new-configure
   

4. That's it! Cabal will now respect all version constraints from the Stackage snapshot, ensuring your dependencies are consistent with the validated package set.

Pro tip: For Cabal 3.0 and later, the new- prefix is optional—you can use cabal configure instead.

If you're working with Nix (to leverage its reproducibility and dependency management), there are a few robust ways to tie your project to a Stackage snapshot:

Using haskell.nix #

This dedicated toolchain integrates Cabal projects with Nix and Stackage seamlessly:

• Initialize your project with haskell.nix (follow the project's setup guide for your specific project structure).
• Specify your target Stackage snapshot (e.g., lts-21.10) in your project's Nix configuration files.
• Build or develop your project with Nix commands like nix-build (to build the project) or nix develop (to enter a reproducible development environment). All dependencies will be pulled directly from the specified Stackage snapshot.

Using cabal2nix + Nixpkgs Stackage Sets #

Nixpkgs includes pre-built package sets for every Stackage LTS and Nightly snapshot. Here's how to use them:

1. Generate a Nix expression for your Cabal project with cabal2nix:

   cabal2nix . > default.nix
   

2. Create a shell.nix file that imports the Nixpkgs revision matching your target snapshot and ties your project to its package set:

   let
     pkgs = import <nixpkgs> { config = {}; overlays = []; };
     # Replace with your target snapshot
     stackageSet = pkgs.haskell.packages.lts-21.10;
   in
   stackageSet.callPackage ./default.nix {}
   

3. Use nix-shell to enter a development environment with all snapshot dependencies, or nix-build to build your project reproducibly.

Minimal nix-shell Environment #

For a quick, lightweight setup, create a minimal shell.nix that gives you a GHC environment tied to your Stackage snapshot:

{ pkgs ? import <nixpkgs> {} }:
pkgs.haskell.packages.lts-21.10.ghcWithPackages (ps: with ps; [
  # Add your project's direct dependencies here, or leave empty for the full snapshot environment
  base text aeson
])

Run nix-shell to enter the environment—any cabal commands you run here will use the dependency versions from the specified Stackage snapshot.

内容的提问来源于stack exchange，提问作者sjakobi