Why reproducibility is breaking by metadata?

[znavko@disroot.org]

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'.