As of recently, Nix 2.6 from Ubuntu 22.04 became too old to evaluate nixpkgs. A new-enough version of Nix is available as part of Ubuntu 24.04, but those newer versions of Nix aren't happy with our rather primitive proot workaround anymore. Thankfully, someone already made a version of Nix that does all the heavy lifting for running in unprivileged environments like the one Read the Docs provides. So we used that instead.
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672 B