Re: Why reproducibility is breaking by metadata?

[Julien Lepiller]

Le 3 juillet 2019 06:05:02 GMT+02:00, address@hidden a écrit :
>Hello, Guix Help! I am translating Guix manual and found that the
>author is entirely given to reproducibility. It leads to such phrases
>that metadata breaks reproducibility when he describes
>'--save-provenance' flag of 'guix pack' command here:
>
>'This option is not enabled by default because, like timestamps,
>provenance information contributes nothing to the build process. In
>other words, there is an infinity of channel URLs and commit IDs that
>can lead to the same pack. Recording such “silent” metadata in the
>output thus potentially breaks the source-to-binary bitwise
>reproducibility property. '
>
>I did not expected such a categorical statement. I think, it does not
>actually break reproducibility but only complicates checks. If we have
>to talk about reproducibility to ignoramus, saying 'this option breaks
>reproducibility option' have to have remark 'simply put' or 'plainly'.

I think the key here is "bitwise": it breaks reproducibility in terms of the 
build results not having the same hash. Does it make sense?