Hash mismatch on nixpkgsSrc

[toonn]

error: hash mismatch in file downloaded from 'https://github.com/NixOS/nixpkgs/archive/110a2c9ebbf5d4a94486854f18a37a938cfacbbb.tar.gz':
         specified: sha256:0v12ylqxy1kl06dgln6h5k8vhlfzp8xvdymljj7bl0avr0nrgrcm
         got:       sha256:1mf8fkdxbk6bwv0gvk1kyh5307wl71ifl7lnzqvs1z1mk1kbhg0g

       … while realising the context of a path

       at /nix/store/j5hw2a8l4w788bya2yg3ibcqh57n7gip-source/default.nix:9:24:

            8|     };
            9|   pkgs = args.pkgs or (import nixpkgsSrc {});
             |                        ^
           10|   flake-compat =

       … while realising the context of a path

       at /nix/store/j5hw2a8l4w788bya2yg3ibcqh57n7gip-source/default.nix:15:10:

           14|     };
           15|   self = import flake-compat {
             |          ^
           16|     # We bypass flake-compat's rootSrc cleaning by evading its detection of this as a git

       … while evaluating anonymous lambda

       at /nix/store/j5hw2a8l4w788bya2yg3ibcqh57n7gip-source/default.nix:1:1:

            1| {...}@args:
             | ^
            2|

       … from call site

       at /Users/toonn/src/nix-config/haskell.nix/nixpkgs.nix:2:16:

            1| let
            2|   haskellNix = import (builtins.fetchTarball
             |                ^
            3|     ( "https://github.com/input-output-hk/haskell.nix/archive/"

       … while evaluating the file '/Users/toonn/src/nix-config/haskell.nix/nixpkgs.nix':

       … while evaluating anonymous lambda

       at /Users/toonn/src/bfpt/default.nix:1:1:

            1| { pkgs ? import ~/src/nix-config/haskell.nix/nixpkgs.nix
             | ^
            2| , compiler-nix-name ? "ghc902"

       … from call site

This is happening for me on x86_64-darwin. A common source of hash mismatches on Darwin is HFS+, which is case-insensitive by default. But this is just a tarball, so a single file and I don't believe that can make the difference.

[michaelpj]

This isn't really anything to do with haskell.nix, though?

[toonn]

That depends. This hash is specified by the haskell.nix project in its default.nix. If x86_64-darwin is considered a supported system then it is a bug in haskell.nix.

[toonn]

I've been looking into this more. It doesn't reproduce on NixOS with Nix 2.3.16 nor Nix 2.11.0, aarch64-darwin with Nix 2.8.1 nor x86_64-darwin with Nix 2.10.3 on APFS.

So it seems pretty specific to my setup.

I've checked all the filenames in nixpkgs for case collisions or differences under NFC/NFD but this hasn't turned up anything.

I'm pretty puzzled 😕

[hamishmack]

But this is just a tarball, so a single file and I don't believe that can make the difference.

I think that nix might extract the files before hashing so that the source does not matter (tarballs and fetchgit for instance get the same hash if all the files match).

[toonn]

Clever helped me troubleshoot this further. Turns out a single bit was flipped in a hash in a package description. So this is entirely on my hardware corrupting a file during fetching or unpacking or something.

Sorry for the noise!

[hamishmack]

See NixOS/nix#847 (comment) and NixOS/nix#2475

My guess is that a unicode character slipped into the nixpkgs source and picked a commit while it was still in there. Hopefully someone has removed it. Let's try bumping the bootstrap nixpkgs to our 22.05 pin.

[toonn]

@hamishmack, thanks for the response. That was my original suspicion but it turned out not to be true. As I said in my previous comment, this was entirely on my hardware. A single bit flipped in the fetched and unpacked source, changing a "p" to a "q" in a hash in a random package in pkgs. This meant the NAR for that source was in fact different and causing a "legitimate" hash mismatch.

I hope this didn't cause too much undue work on your part! ❤️