202510 Snippets

Linkpost for October 2025. Learning JJ, some fun posts and a nix cache presence check snippet. 2025-10-20

by Luna Nova

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Fun§

• How I, a non-developer, read the tutorial you, a developer, wrote for me, a beginner
• It took 5 years but a tiny tweak to xdg-desktop-portal's docs to make it clear that OpenFile works for dirs, and OpenDirectory on a dir opens the dir containing the target dir got merged. Woohoo! It's amusing when something lands after so long.
• Building a Bimetallic Tea Monitoring Mechanism
  • I love the project but if you're copying them I'd avoid leaded (free-maching) brass for any components. Just because they don't stay in the tea doesn't mean it's a good idea to use them in something you'll be handling while drinking and need to wash.

Development§

Nix cache presence from flake ref§

Check if some flake refs are in a binary cache:

$ echo github:nixos/nixpkgs/{release-25.05,master}#ollama-rocm | xargs -n1 sh -c 'nix eval --raw "$1"; echo' -- | xargs -n1 nix path-info --store https://cache.nixos.org
/nix/store/kds9g0m2fhknx051gblg1d5lz52clf23-ollama-0.11.10
/nix/store/hd4lwgnfag8x8b8kir69lw2qhq8vhx2n-ollama-0.12.5
$ echo github:nixos/nixpkgs/staging#ollama-rocm | xargs -n1 sh -c 'nix eval --raw "$1"; echo' -- | xargs -n1 nix path-info --store https://cache.nixos.org
don't know how to build these paths:
  /nix/store/w1xxhfd5y0v5jbm19gzqlb4xa63bb1ym-ollama-0.12.5
error: path '/nix/store/w1xxhfd5y0v5jbm19gzqlb4xa63bb1ym-ollama-0.12.5' does not exist in the store

I couldn't work out how to do this without two separate steps so it's a little janky. 1. get out path 2. check if that path exists.

nix eval needs to use a writeable store to instantiate the drv in, nix path-info needs to be against the remote cache. --readonly-mode which stores evaluated drvs in memory instead of to the store isn't available for the flake command UI, only for nix-instantiate.

learning jj-vcs§

• steve's jj tutorial
• stupid jj tricks
• flames of code's jj workflow

Mistakes§

Oops, I picked up all these bookmarks I don't want from a remote
…this is annoying to clean up
…ok got it we can pass a template that uses the name only and skips the remote part

$ jj bookmark list --remote upstream -T 'concat(self.name(), "\n")' \
    | grep -v -E '^(master|nixos-unstable|staging|staging-next)$' \
    | xargs jj bookmark forget --include-remotes
Forgot 29 local bookmarks.
Forgot 29 remote bookmarks.

@misc{202510-snippets,
    author = {Luna Nova},
    title = {202510 Snippets},
    year = {2025},
    url = {https://lunnova.dev/articles/202510-snippets/},
    urldate = {2025-10-20}
}

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