Comment by Izkata
14 hours ago
> whereas nix will always produce the same output for a given input.
If they didn't take shortcuts. I don't know if it's been fixed, but at one point Vuze in nix pulled in an arbitrary jar file from a URL. I had to dig through it because the jar had been updated at some point but not the nix config and it was failing at an odd place.
This should result in a hash mismatch error rather than an output different from the previous one. If there is a way to locate the original jar file (hash matching), it will still produce the same output as before.
Flakes fixes this for Nix, it ensures builds are truly reproducible by capturing all the inputs (or blocking them).
No it doesn't. If the content of a url changes then the only way to have reproducibility is caching. You tell nix the content hash is some value and it looks up the value in the nix store. Note, it will match anything with that content hash so it is absolutely possible to tell it the wrong hash.
Apparently I made note of this in my laptop setup script (but not when this happened so I don't know how long ago this was) so in case anyone was curious, the jar file was compiled with java 16, but the nix config was running it with java 8. I assume they were both java 8 when it was set up and the jar file upgraded but don't really know what happened.