nixpkgs-fmt should support excluding files

[lovesegfault]

Is your feature request related to a problem? Please describe.
In our repo we have a few autogen'd Nix files, such as Cargo.nix from crate2nix and sources.nix from niv. These aren't properly formatted, but I don't want our CI to fail because of that.

Describe the solution you'd like
I want to be able to ignore certain files in my nixpkgs-fmt call. For example nixpkgs-fmt . --not "Cargo.nix"

Describe alternatives you've considered
Here's my ugly alternative:

find . -iname "*.nix" \
    -not -path ./Cargo.nix \
    -not -path ./nix/sources.nix \
    -exec nixpkgs-fmt --check {} +

[zimbatm]

Hey @lovesegfault, try adding a .ignore file with the pattern to exclude. It should be in the same form as the .gitignore files. We use the ignore crate which seems to be using that file but haven't test it myself.

[lovesegfault]

That works!

I'd still like for this to be doable from the cli, though. I'm not keen on these special files :/

[zimbatm]

yeah agreed, this issue is not solved

[bhipple]

Another standard technique is being able to put something like # yapf: disable or // clang-format: disable as a comment in the header of the file.

For nixpkgs specifically, the nixpkgs-update bot has some support for reading these type of comments and leaving a file alone if they contain them:
https://github.com/ryantm/nixpkgs-update/blob/master/src/Blacklist.hs#L117

[camelpunch]

The README says you can use --exclude GLOB, but this doesn't appear to work:

$ nixpkgs-fmt --exclude deps.nix
error: Found argument '--exclude' which wasn't expected, or isn't valid in this context

USAGE:
    nixpkgs-fmt [FLAGS] [OPTIONS] [FILE]...

For more information try --help

[zoechi]

.ignore and .gitignore didn't work for me