Nixpkgs: Placeholder for sha256s to avoid length check

Created on 28 Jun 2018 · 11Comments · Source: NixOS/nixpkgs

Issue description

Often when writing a new nix expression I am faced with the need to make up with a valid sha256 just to try evaluating the expression and pull the real hash from the resulting error. The hash validity check makes this unnecessarily cumbersome since I need to find a hash elsewhere and then modify it to ensure that a rebuild occurs.

I suggest that the hash attribute validation learn to accept a particular placeholder string (e.g. !) as a valid digest. This would remove a great deal of friction from the process of crafting an expression.

Source

bgamari

👍8

Most helpful comment

You are all heretics because clearly 64 zeros are the way to go. At least you don't need to remember weird constant 52. (64 base-16 4-bit nibbles is obviously 256, and 256 is in the name of the hash)

7c6f434c on 29 Jun 2018

😄1 👍1

All 11 comments

FWIW I just insert 52 1's, which in vim can be done with: "52i1" or so. But this is more of a learned workaround than something "good" :).

dtzWill on 28 Jun 2018

and C-u 52 C-u 1 for users of the one true editor.

matthewbauer on 29 Jun 2018

You are all heretics because clearly 64 zeros are the way to go. At least you don't need to remember weird constant 52. (64 base-16 4-bit nibbles is obviously 256, and 256 is in the name of the hash)

7c6f434c on 29 Jun 2018

😄1 👍1

As a workaround I prefer to go to the start of the string and then type this vim:
vt"r0
So I do not need to care about length, but still I need to copy some random hash.

Luz on 29 Jun 2018

An alternative is that in the case of a missing hash attribute, the correct hash is reported in a user friendly manner.

mpickering on 30 Jun 2018

👍1

I have a snippet in Atom (_hides_):

'.source.nix':
  'sha256 hash':
    'prefix': 'sha256'
    'body': '''
        sha256 = "${1:0000000000000000000000000000000000000000000000000000}";
      '''

An alternate solution would be to make something available that you can plugin as a placeholder, say lib.emptyhash

Synthetica9 on 1 Jul 2018

@bgamari given all these suggestions can this issue be closed now?

aanderse on 9 Feb 2019

@aanderse From my perspective, the issue it not resolved at all. These are all work arounds.

mpickering on 9 Feb 2019

Thank you for your contributions.

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