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Add an example of version pinning with flakes (#172)

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Walter Huf 2024-07-17 18:41:16 -07:00 committed by GitHub
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docs/nixos-with-flakes/downgrade-or-upgrade-packages.md
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@ -102,6 +102,26 @@ submodule. Here's an example of a Home Manager submodule:
}
```
## Pinning a package version with an overlay
The above approach is perfect for application packages, but sometimes you need to replace libraries used by those packages. This is where [Overlays](../nixpkgs/overlays.md) shine! Overlays can edit or replace any attribute of a package, but for now we'll just pin a package to a different nixpkgs version. The main disadvantage of editing a dependency with an overlay is that your Nix installation will recompile all installed packages that depend on it, but your situation may require it for specific bug fixes.
```nix
# overlays/mesa.nix
{ config, pkgs, lib, pkgs-fd40cef8d, ... }:
{
nixpkgs.overlays = [
# Overlay: Use `self` and `super` to express
# the inheritance relationship
(self: super: {
mesa = pkgs-fd40cef8d.mesa;
})
];
}
```
## Applying the new configuration
By adjusting the configuration as shown above, you can deploy it using
`sudo nixos-rebuild switch`. This will downgrade your Firefox/Chrome/VSCode versions to
the ones corresponding to `nixpkgs-stable` or `nixpkgs-fd40cef8d`.