Pinning Inputs with Mirrors

Mirrors are a very good idea for project to have.

Increases project resiliance as all servers go down so ideally something should be online to fallback to
Helps accessibility as some regions block users based on sanctions & others might not agree to the terms of service or privacy laws in the jurisdiction of some options
If self-hosted, then you/your project owns the code — which can help with potential censorship

At the time of writing, Nix flakes does not & cannot support mirrors in input pinning requiring an input pinner like Nixtamal to automate it.

How to pin a repository with mirrors in Nix + Nixtamal

Mirrors are not supported on all kinds (fetcher limitations) however these can be supported:

File
Archive
Darcs
Pijul
Git (only in eval time fetching using builtins.fetchGit)

Let’s show the way using the Soupault repository, but if it’s one of the supported kinds, any will work.

Latest revision

// manifest.kdl
inputs {
	soupault {
		archive {
			url "https://codeberg.org/PataphysicalSociety/soupault/archive/{{fresh-value}}.tar.gz"
			mirrors "https://github.com/PataphysicalSociety/soupault/archive/{{fresh-value}}.tar.gz"
		}
	}
	fresh-cmd {
		$ git ls-remote --branches main "https://codeberg.org/PataphysicalSociety/soupault.git"
		| cut -f1
	}
}