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Allow empty hashes #3544

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Allow empty hashes #3544

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matthewbauer
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This allows hash="" so that it can be used for debugging purposes. For
instance, this gives you an error message like:

warning: found empty hash, assuming you wanted 'sha256:0000000000000000000000000000000000000000000000000000'
hash mismatch in fixed-output derivation '/nix/store/jx3gikmipizpk181cgfa1l4wwcamy6p0-nixpkgs':
wanted: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
got: sha256-Wm7FDDnzNteClYOn+LRCtPNcK9wjEtpj+k9IIfygD7o=

@matthewbauer
Allow empty hashes
e96955d 
This allows hash="" so that it can be used for debugging purposes. For
instance, this gives you an error message like:

warning: found empty hash, assuming you wanted 'sha256:0000000000000000000000000000000000000000000000000000'
hash mismatch in fixed-output derivation '/nix/store/jx3gikmipizpk181cgfa1l4wwcamy6p0-nixpkgs':
  wanted: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
  got:    sha256-Wm7FDDnzNteClYOn+LRCtPNcK9wjEtpj+k9IIfygD7o=
@matthewbauer matthewbauer mentioned this pull request Apr 28, 2020
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@NorfairKing
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@matthewbauer I think the only argument against this is that 0 may be a valid hash (I don't think it's likely, but still).
Could we instead just always print the gotten hash, even if the wanted hash was of incorrect length?

That being said, I think this is already an improvement and my suggestion is about a case that practically should not happen. (Unless the hash on an empty string is 0).

@edolstra
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I think we have to be very careful about this not having unintended side effects. It seems safer to handle this at a higher level than in the Hash type (which is used all over the place).

@edolstra
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An example of "higher level" would be fetchurl, which could set a dummy hash if none is specified, or prim_derivationStrict (but it would have to be careful not to turn normal derivations into fixed-output derivations with a dummy hash).

@matthewbauer
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Right - a more explicit try / catch here would be better.

@edolstra
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edolstra commented Jun 2, 2020 •
edited

Will close this PR for the reason mentioned above.

@edolstra edolstra closed this Jun 2, 2020
matthewbauer added a commit to matthewbauer/nix that referenced this pull request Jun 9, 2020
@matthewbauer
Allow empty hash in derivations
762273f 
follow up of NixOS#3544

This allows hash="" so that it can be used for debugging purposes. For
instance, this gives you an error message like:

  warning: found empty hash, assuming you wanted 'sha256:0000000000000000000000000000000000000000000000000000'
  hash mismatch in fixed-output derivation '/nix/store/asx6qw1r1xk6iak6y6jph4n58h4hdmbm-nix':
    wanted: sha256:0000000000000000000000000000000000000000000000000000
    got:    sha256:0fpfhipl9v1mfzw2ffmxiyyzqwlkvww22bh9wcy4qrfslb4jm429
@matthewbauer matthewbauer mentioned this pull request Jun 9, 2020
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@matthewbauer
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updated with changes here:

#3674

please take a look when you get a chance to.

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3 participants
@matthewbauer @NorfairKing @edolstra