What's the story of build reproducibility of snaps?

[abitrolly]

I made empty snap that is being automatically rebuilt every time on CI/CD run. Reproducible builds may help avoid new releases if package contents didn’t change.

I decided to see how these empty snaps differ. First I downloaded all my snaps history.

Improvements in snap download

To bulk download of my snap history I used something like this. export SNAP=yakshaveinc export FROM=1 export TO=74 snapcraft export-login --snaps=$SNAP --acls=package_access ysi.download for i in $(seq $FROM $TO); do UBUNTU_STORE_AUTH_DATA_FILENAME=ysi.download snap download $SNAP --target-directory=ysi --revision=$i; done rm ysi.download

Then I used https://diffoscope.org/ to compare two latest snaps (this forum does not support attachments) and here is the result I get.

The only difference is the timestamp that is repeated four times through the file.

✗ unsquashfs -s yakshaveinc_73.snap
Found a valid SQUASHFS 4:0 superblock on yakshaveinc_73.snap.
Creation or last append time Tue May 26 20:27:38 2020
...
✗ unsquashfs -s yakshaveinc_74.snap
Found a valid SQUASHFS 4:0 superblock on yakshaveinc_74.snap.
Creation or last append time Wed May 27 14:25:37 2020
...