Flake setups are not reliably detected
emilazy opened this issue · comments
I have an all-flakes nix-darwin/home-manager setup but the command-not-found.sh script gives me nix-shell output. It seems like I have no user profile to look for a manifest.json in:
emily@yuyuko ~> ls -l ~/.nix-profile
lrwxr-xr-x 1 emily staff 44 20 May 10:49 /Users/emily/.nix-profile@ -> /nix/var/nix/profiles/per-user/emily/profile
emily@yuyuko ~> ls -l /nix/var/nix/profiles/per-user/emily/profile
ls: /nix/var/nix/profiles/per-user/emily/profile: No such file or directory
I'm not sure what a reliable way to detect a flakes setup is, though.
Would it make more sense if command-not-found.sh looks at the enabled experimental features instead?
Maybe; I can see people using e.g. https://github.com/DeterminateSystems/nix-installer with a conventional non-flakes setup and getting unexpected results because of the defaulted-on experimental feature. Not sure if that's worth worrying about though. Is there an easy way to check the experimental features without trying to parse nix.conf?
One possibility would be to check if "nix registry list" is successful?
we can run nix show-config experimental-features and check if it contains flakes
but that will break if flakes is no longer an experimental feature, right?
yeah that's true, though I'm a bit worried that nix registry list and other flakes commands would try to download/refresh the flake registry and slow down command-not-found
true, so let's check for nix show-config experimental-features and later add a version check if nix ever makes flakes support non-experimental?
sounds good to me, and we can just do a nix --version check once that happens
For what it's worth it seems like nix show-config experimental-features and nix --version are both noticeably kind of slow for me, maybe because they're unconditionally poking the daemon or something:
emily@yuyuko ~> hyperfine --warmup 3 'nix --version' 'nix show-config experimental-features' 'rg experimental-features /etc/nix/nix.conf'
Benchmark 1: nix --version
Time (mean ± σ): 81.0 ms ± 4.0 ms [User: 67.0 ms, System: 12.0 ms]
Range (min … max): 75.6 ms … 90.3 ms 34 runs
Benchmark 2: nix show-config experimental-features
Time (mean ± σ): 78.2 ms ± 4.0 ms [User: 64.9 ms, System: 11.3 ms]
Range (min … max): 74.2 ms … 91.3 ms 37 runs
Benchmark 3: rg experimental-features /etc/nix/nix.conf
Time (mean ± σ): 7.5 ms ± 0.8 ms [User: 4.1 ms, System: 2.2 ms]
Range (min … max): 5.2 ms … 9.3 ms 255 runs
Summary
rg experimental-features /etc/nix/nix.conf ran
10.38 ± 1.18 times faster than nix show-config experimental-features
10.76 ± 1.21 times faster than nix --version
(Though I find command-not-found already a bit too slow for my tastes, so up to you whether that is reason to avoid making it worse or a reason it's not that big of a deal.)
Just opened #227 to rewrite command-not-found.sh in rust, hoping to improve a few things including this one
the new flakes detection logic parses the nix config file and looks for flakes in experimental-features and should be able to solve the issue
https://github.com/figsoda/nix-index/blob/0a9ed9273a6283ff79e93cef87b6bca3b1c344e1/src/bin/nix-locate.rs#L163