feature: add a command to remove gc roots for old or removed projects

[symphorien]

I copied the functionality and option names of nix-store --gc --print-roots and nix-collect-garbage --delete-older-than. To print the original project a gc root corresponds to, I store a symlink to the shell.nix file along with the gc root.

• [x] Amended the changelog in release.nix (see release.nix for instructions)

[Profpatsch]

Before looking at this PR, here’s an unprimed design mockup of what I’d expect the gc root cleaning CLI to look like:

GC

lorri gc info

Shows info about projects (shell files) that exist and have been evaluated.

Shows info about which projects don’t have a corresponding directory (or just can’t be reached anymore)

--json prints a json representation that can be parsed in scripts. It contains

• The shell file path
• Whether the shell file is still accessible (i.e. the project got deleted or moved)
• The last derivation generated for the project (?)
• The gc root for the store path
• The timestamp of when the project was evaluated (or built?) last.

lorri gc rm --shell-file path/to/shell.nix --shell-file …

Removes any gc roots to the shell file, so that the next nix garbage collect removes the project store paths.

Removes the project from lorri’s database.

Afterwards runs nix-store --delete on all drvs and store paths that we know about (how to determine? Do we have references to the store paths? Or do we need an extra nix-store --query to find the paths?

Since there is no way to figure out if a drv has some IfD-paths it instantiates (is there?), we should print a message to run nix-store --gc to remove all artifacts, also the ones from previous runs.

lorri gc rm --all

Removes all gc roots that were created by lorri.

Convenience for parsing gc info --json and constructing a long gc rm command line with all files.

lorri gc rm --older-than=\<days>

Removes all gc roots that haven’t been updated <days> ago.

Convenience for parsing this information from the gc info --json output and creating a gc rm command line with all files.

[symphorien]

I implemented something very close to what you proposed. Differences:

• lorri gc rm always removes roots to projects that were removed, like nix-store --gc removes dead paths
• lorri gc rm does not remove store paths, it advises users to run nix-store --gc themselves.

[symphorien]

I rebased but ci fails because cachix/cachix-action is out of date.

[symphorien]

I pushed a commit updating nix-related actions. It fixes CI on ubuntu at least.

[symphorien]

could you review again, @Profpatsch ?

[symphorien]

ping @Profpatsch

[nyarly]

@symphorien Apologies for letting this linger so long. Could you merge canon back to your branch? Notably, the CI configs need to be updated (I think -X theirs would work fine)

[symphorien]

done

[symphorien]

ci fixed :)