Can I use flakes within a git repo without committing flake.nix?

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After having watched the question on SO for nearly 2 weeks now, I am kind of curious how you managed to not get downvoted much, as the question in prose is quite different from what to expect when reading the subject…

Anyway…

  1. what is the difference?

The difference between path and git+file is quite obvious… path just treats the full filesystem location as the base of the flake, git+file tries to read the flakes content from a git repository. This is explained in the manual. https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#types which has already been linked.

  1. what is self-contained / hermetic evaluation?

In quite simple terms, this means, that everything required is included, a declared input or by definition always available.

So a US military MRE is “self-contained” as you just need to add some tap-water and due to some chemical reaction in the outer bag, it will heat up the contents of the inner bag. Tap-water is considered to be always available.

A can of beans though is not self contained, as you require to have a can opener and a camp fire.

  1. git-flake-evaluation is hermetic, but is path-flake-evaluation hermetic?

Yes, both are hermetic and pure. But a git-type is easier to send and reason about, and to check if you are really looking at the same code.

  1. does nix build git+file:. have some additional caching, that nix build path:. doesnt have?

Yes. Evaluation cache can only work on “snapshottable” flake types.

  1. why not make nix build . just equal to nix build path:., instead of this find type automatically behavior, described above (Because: what problem its trying to solve? The problem, solutions to which require all these weird behaviors, like unsolicited git add behind the scenes? But I can easily get around/silence it with path:.? This design is so weird, reason is so shady)

To avoid surprises when you share your code. In general defaulting to the version control system is sane, as one can assume that you want to use the version control to share your code.

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